LIDAR Analyst 5.1 Tutorial

(1)

(2)

LIDAR Analyst

Tutorial

5.1.X

(3)

LIDAR Analyst® 5.1.x for ArcGIS® Tutorial

Copyright Notice

Trademarks

LIDAR Analyst® is a registered trademark of Overwatch Systems, Ltd., an operating unit of Textron Systems Corporation, a Textron Inc. (NYSE: TXT) company. We put the information in GIS is a service mark of Overwatch, ESRI, ArcGIS, ArcMap, ArcView, ArcScene, 3D Analyst and Spatial Analyst are trademarks, registered trademarks, or service marks of Environmental

Systems Research Institute, Inc. Google Earth™ mapping service is a trademark of Google Inc. Windows® is a registered trademark of Microsoft Corporation in the United States and other countries. Virtual Earth™ mapping service is a trademark of Microsoft Corporation.

The names of other companies and products herein are trademarks or registered trademarks of their respective owners.

The content of this guide is furnished for informational use only, is subject to change without notice, and should not be construed as a commitment by Overwatch Systems, Ltd. Overwatch Systems, Ltd. assumes no responsibility or liability for any errors or inaccuracies that may appear in this book. This is not a comprehensive guide to the LIDAR Analyst software. Graphics and other illustrations are for reference only.

Export Notice

The software and associated documentation whose export, transfer, diversion, disclosure and further publication is restricted by the applicable export laws and regulations of the United States of America, including the Export Administration Act of 1979, as amended, and the Export

Administration Regulations. Violations of these laws and regulations are subject to severe civil, criminal and administrative penalties.

(4)

LIDAR Analyst 5.1.x Tutorial| i

Chapter 1

Introduction

Overwatch’s LIDAR Analyst® allows you to quickly and easily extract features using a point cloud or first and last return LIDAR data. LIDAR Analyst is a 3D feature extraction solution for airborne LIDAR (Light Detection and Ranging) data, supporting defense, academia, environmental organizations, and almost every field in the GIS industry requiring high resolution terrain information.

Through the power of automation, the LIDAR Analyst software radically simplifies the process of extracting bare earth, buildings, and trees/forest features. LIDAR Analyst provides tools for Automated Feature Extraction (AFE), Digital Elevation Model (DEM) editing, modification of bare earth surfaces, hillshading and relief, squaring of building footprints, and data attribution for buildings, tree points, and forest polygons.

In This Chapter

LIDAR: A Brief Overview ... 2 LIDAR Analyst Basics ... 4

(7)

2 | Introduction Chapter 1

LIDAR: A Brief Overview

LIDAR is an acronym for Light Detection And Ranging. This recent technology, which reveals variations in elevation, is used for determining the shape of the ground surface with the inclusion of natural and man-made features. LIDAR data is used to map topographic features as well as the height and density of raised objects, such as trees and buildings, on the surface of the earth. Raw LIDAR data, also called a point cloud, is collected from aircraft by firing laser beams to the earth. LIDAR sensors transmit laser light pulses in visible and near infrared wave lengths to the earth’s surface.

Upon hitting solid objects, the beams are reflected back to the LIDAR sensor. Elevation data (object height) are calculated by measuring the time required for the signal to travel to the object surface and back to the sensor. With this information, the actual height of buildings and other raised objects or topographic features can be calculated. Laser pulses can have multiple

reflections from a single beam, enabling detailed modeling of terrain surface. Part of a beam can hit a solid object and reflect back to the sensor while the rest of the beam continues toward the ground. This commonly occurs in forested or urban areas.

Multiple reflections can determine intermediate surfaces such as tree canopy, providing elevation data for objects other than ground. Ideally, the first return hits the top leaves of the canopy and the last return travels through a gap to hit the ground under the canopy. Multiple reflections create a better surface model, since they enable the collection of more ground points in forested or urban areas.

LIDAR Data

LIDAR point data is collected in a swath. Each laser return results in a data point with x, y, and z coordinates, where x is longitude, y is latitude, and z is elevation.

The reflective intensity, or strength of the reflected laser pulse, is commonly collected along with the other data. Good intensity data produces an image comparable to a black and white

photograph. Intensity data can be used for visualization of your data and referencing features for extraction.

The two primary results derived from raw LIDAR data are the last-return data file and the accompanying first-return data file.

(8)

LIDAR Analyst 5.1.x Tutorial | 3 LIDAR: A Brief Overview

First and Last Return

Each light beam transmitted, from an aircraft, to the earth results in one or up to five reflections. A reflection or return is defined as the portion of a light beam that hits the surface of an object and travels back to the sensor. In areas containing surfaces smaller than the beam radius, multiple reflections can occur.

When the light beam (or laser) comes in contact with an object in such a way that the incident energy is only partially reflected back to the sensor, the remaining incident energy continues traveling downward until it comes into contact with another solid object. I any additional objects, in the continuing path of the beam, reflect sufficient laser energy back to the sensor, will be detected. The first portion of the beam, that hits an object such as a branch or leafy area of a tree, is reflected back to the sensor is called the first return. First return data contains elevations from the first surfaces the laser comes in contact with. The portion of the beam that strikes a final object (such as the ground) and goes back to the sensor is referred to as the last return. Last return data contains elevations from the subsequent hits and the final incident energy strike.

Since the first return data contains the elevations of the tallest features in a dataset (the light beam hits the highest object first) and the last return has the strongest probability of hitting the actual ground surface, using first and last return data is useful for extracting building, tree, and bare-ground elevations. Returns between the first and last returns often strike intermediate objects, such as tree branches, and are useful for studying the canopy structure of forest.

Point Clouds

Raw LIDAR data derived from a pulse returns is a point cloud. The multiple reflections of the laser beam create a multi-return point cloud. At the very least, the point cloud contains elevation values for all returns, with each point defined by the associated x, y, and z coordinate values.

The density of the point cloud is usually specified by the manager for the LIDAR project.

Depending upon the LIDAR acquisition sensor and the format and fields requested by the project manager, the point cloud can store additional data such as return information, intensity, time, and aircraft altitude.

Point cloud data is stored in many different formats, from ASCII (text, CSV, etc.) to binary (bin, LAS, proprietary formats). Increasingly, due to user demand, point clouds are being delivered as LAS (Log ASCII Standard) files, which are standardized, typically smaller, and can be used in multiple applications.

(9)

4 | Introduction Chapter 1

LIDAR Analyst Basics

LIDAR Analyst imports and processes data returns in several formats.

Import LIDAR data returns in a variety of point-feature and grid-data formats, including LAS, ASCII, GeoTIF, and ArcGRID

Convert LIDAR data returns in text file format to the LAS file format Process elevation data in LAS file format or DEM raster format Process data in different horizontal and vertical map units

Output terrain and features, including bare earth (raster), buildings (vector), trees (vector), and forests (vector)

Classify LAS point clouds based on LIDAR Analyst extractions and user settings

In addition, LIDAR Analyst provides precise extraction algorithms for bare earth, buildings, and trees and forest features, enabling faster processing, allowing larger datasets, and improving accuracy. The interface includes parameter customization to refine the level of detail in extraction of terrain and culture features.

Visualize LIDAR data with a powerful 3D visualization application, and enhanced analysis tools

Import point clouds stored in a text file or shapefile Crop LAS files

Edit DEMs by adding/removing points when generating bare earth, and defining regions to which you can apply various DEM modification processes

Extract multi-component/complex buildings and update z-values and attributes after editing with building reshape, building auto-split, and courtyard cleanup tools

(10)

Chapter 2

Installation and Activation

In This Chapter

(11)

6 | Installation and Activation

Prerequisites and Installation

Prerequisites and Installation

LIDAR Analyst for ArcGIS Prerequisites

LIDAR Analyst requires the following prerequisites:

Platform Program

ou must have the ArcGIS® program installed on the computer on which you are installing LIDAR Analyst. Feature Analyst and LIDAR Analyst support versions 9.3, 10.0, 10.1 and 10.2 of ArcGIS.

Administrative Permission

Confirm you have Administrative Privileges on the computer on which you will be installing LIDAR Analyst. If you do not have Administrative Privileges, contact your System Administrator to install the product for you or request that you have read/write permissions for the installation directory. The default installation directory for 32-bit systems is: C:\Program

Files\Overwatch\Geospatial Modules.

The default installation directory for 64-bit systems is: C:\Program Files(x86)\Overwatch\Geospatial Modules.

Uninstall Previous Version

If you have a 4.x or 5.0 version of LIDAR Analyst installed on your computer, you must uninstall it before installing the new version. Also, some computer configurations will not allow the installation of version 5.1.x if you have a 3.x version installed. If this is the case, uninstall the 3.x version.

Software Requirements

LIDAR Analyst 5.1.x for ArcGIS® requires Microsoft .NET Framework 2.0 in order to install successfully. Upon installation this requirement will be checked and you will be notified if .NET needs to be installed.

Before Installing LIDAR Analyst

Before installing LIDAR Analyst ensure the following steps are complete. Install ArcMap.

(12)

LIDAR Analyst 5.1.x Tutorial | 7 Prerequisites and Installation

Installing and Activating Overview

The LIDAR Analyst installation, licensing, and activation process is easy. You need to:

1. Ensure you have all the necessary prerequisites.

2. Install and activate LIDAR Analyst as an ArcGIS extension.

3. Submit a license request and install the license received by Overwatch. If you are running the tutorial, you do not need to complete this step.

4. Configure the LIDAR Analyst toolbar to display in ArcGIS. In some cases, you may need to display the LIDAR Analyst toolbar. See Displaying the LIDAR Analyst Toolbars (on page 9) for more information.

This guide covers standard licensing installation. For more information about installation and licensing options, refer to the LIDAR Analyst Install Guide.

Note: You DO NOT need a license to run the LIDAR Analyst Tutorial.

Installing LIDAR Analyst

This procedure covers basic installation. For more information, refer to the installation guide. To install LIDAR Analyst:

1. Double-click on the LIDAR_Analyst_5_1_ArcGIS.exe to run the install application. The Overwatch LIDAR Analyst 5.1 for ArcGIS – InstallShield Wizard dialog displays. You are prompted to wait while the installer is extracting the installation files. Once extraction is completed you are allowed to continue to the next step in the installation wizard.

2. Click Next. The LIDAR Analyst for ArcGIS License Agreement dialog box displays. Read the Software License Agreement and if acceptable, select I Accept and choose Next.

3. Read the Software License Agreement and if acceptable, select I Accept and click Next. The Customer Information dialog displays.

4. Enter User Name and Organization.

5. Once you have entered your information click Next, The Destination Folder page displays. Use this dialog to specify a custom installation location.

6. Click Next. The Setup Type page displays.

7. Select Complete and click Next to install all components and proceed directly to the Ready to Install the Program page. Otherwise, select Custom and click Next to configure optional features in the Custom Setup page. The optional features to install are the 3D Viewer and Tutorial Files. Once configured features are selected click Next to proceed to the Ready to Install the Program page.

8. Click Install to begin the installation process. Click Back to go to any previous pages. 9. Click Finish on the InstallShield Wizard Completed page to exit out of the installer.

(13)

8 | Installation and Activation Chapter 2

Activating the LIDAR Analyst Extension

Once LIDAR Analyst is installed, you must activate it as an extension of ArcGIS before you can run the application. Activation enables you to access the LIDAR Analyst toolbars and functions within the ArcGIS workspace.

To activate LIDAR Analyst:

1. Open ArcMap. ArcMap displays.

2. From ArcMap, select Customize > Extensions. The ArcMap Extensions dialog opens, displaying a list of registered extensions available for your version of ArcGIS.

Figure 1: Extensions Dialog

3. Select LIDAR Analyst, and then click Close. LIDAR Analyst is activated. The toolbar displays in ArcMap. If you successfully activated LIDAR Analyst and you don't see the toolbar, follow steps for Displaying the LIDAR Analyst Toolbars (on page 9).

(14)

LIDAR Analyst 5.1.x Tutorial | 9 Prerequisites and Installation

Displaying the LIDAR Analyst Toolbars

LIDAR Analyst has its own toolbars that are accessed directly from ArcMap. It includes the default LIDAR Analyst, the Building Edit, and the Bare Earth toolbars. If you just activated LIDAR Analyst you may need to configure ArcMap to display the toolbars.

The LIDAR Analyst toolbars, as with other ArcMap toolbars, can be shown, hidden, and moved as preferred.

To display the LIDAR Analyst toolbars: 1. If needed, start ArcMap.

2. Do either of the following:

Choose Customize > Toolbars > LIDAR Analyst Toolbar.

Right-click the toolbar area, and select Customize > LIDAR Analyst toolbar from the menu.

The LIDAR Analyst toolbar displays in ArcMap.

Don't see the LIDAR Analyst toolbar?

Once you install LIDAR Analyst, you may need to display the LIDAR Analyst toolbar. Additional Overwatch commands are also available that can be added to any toolbar. See Customizing the

Toolbar (see "Adding Tools to a Toolbar" on page 20) for more information.

Optional LIDAR Analyst 3D Viewer

The LIDAR Analyst 3D Viewer feature allows you to view point clouds, bare earth and LIDAR Analyst based feature extractions.

Installing LIDAR Analyst 3D Viewer

LIDAR Analyst 3D Viewer is part of the default install configuration of LIDAR Analyst.

When installing LIDAR Analyst, either select the Complete installation or if selecting a Custom install make sure the 3D Viewer feature is configured to install. If this is done, the 3D Viewer is installed as a part of LIDAR Analyst.

(15)

10 | Installation and Activation Chapter 2

Opening the 3D Viewer

Once you have installed LIDAR Analyst 3D Viewer, you can open the application. To open LIDAR Analyst 3D Viewer:

Select Windows Start > Programs > All Programs > Viewer 3D > Launch Viewer 3D. The 3D viewer launches.

You can also open directly from the LIDAR Analyst or LIDAR Analyst 3D toolbars.

Click the Open 3D View button on the LIDAR Analyst (on page 19) or LIDAR Analyst 3D toolbars. Launching the 3D Viewer from within ArcGIS allows you to sync views between the 3D Viewer and ArcGIS.

(16)

Chapter 3

Getting Started

In This Chapter

(17)

12 | Getting Started

LIDAR Analyst Tools and the ArcMap Interface

LIDAR Analyst Tools and the ArcMap Interface

Once you have installed, licensed*, and configured ArcMap to display the LIDAR toolbars, you can start working with the available tools. LIDAR Analyst includes three toolbars - LIDAR Analyst, LIDAR Analyst Building Edit, and LIDAR Analyst Bare Earth. Additional commands and options are also available and can be added to any toolbar

LIDAR Analyst toolbars (A) can be docked at the top of the ArcMap interface. Most tasks are initiated from these toolbars or by using the layer shortcut menus in the ArcMap table of contents (B).

*Tutorial users do not need a license.

(18)

LIDAR Analyst 5.1.x Tutorial | 13 LIDAR Analyst Tools and the ArcMap Interface

Table of Contents (ArcMap)

The ArcMap table of contents includes data frames and layers. Each layer has a shortcut menu with available options. You can also configure layer options depending on the type. For example, you can change the symbol settings.

Tutorial Note: When you open the LIDAR Analyst Tutorial Project, all the lessons in the Project

are loaded into the ArcMap table of contents. Each lesson is contained in a separate data frame. Each data frame lists all the layers in the lesson.

The follow diagram is an example of some of the layer options available.

Figure 3: Table of Contents

a) Data frame - A data frame must be activated in order to work in it. Only one data frame can be active at a time. The active data frame name appears in bold letters.

b) Layer - Right-clicking a layer displays shortcut menu of options.

c) Expand/Collapse Layer - Click the plus [+] to expand layer or the minus [-] to collapse layer. d) Symbol - Double-clicking the symbol (green shown) opens the Symbols dialog.

e) Band Information - Click the band to display a menu of options. f) Color Ramp - Click the color ramp to open the Color Ramp dialog.

g) Shortcut menus - Right-click a layer displays a context menu. Options vary depending on layer selected.

(19)

14 | Getting Started Chapter 3

Working with Layers in the Table of Contents

The ArcMap table of contents includes several options for adjusting layers and accessing functionality.

Activating a Data Frame

A data frame must be activated to work on it. Only one data frame can be active at a time. 1. Right-click on the data frame in the table of contents (on page 13). A menu displays. 2. Select Activate. The data frame text changes to bold indicating the data frame is active.

Figure 4: Active Data Frame in ArcMap

Expanding and Collapsing Layers

You expand the data frame to show more information and collapse as needed. Click [+] to expand the layers.

Click [-] to collapse layers.

Showing and Hiding Layers

The check box next to each file in the table of contents (on page 13) indicates whether or not the image is currently displaying in the workspace. Select or clear the check box next to the layer.

(20)

Changing Layer Symbology

Layer symbols are easily customized from the table of contents. To change layer symbology:

1. Click the color symbol to the left of the text in the table of contents. The ArcMap Symbol Selector dialog displays.

Figure 5: Symbol Selector Dialog

2. Do any of the following:

Select an existing symbol from the list.

Create your own using the fill, outline, and other options.

(21)

ArcMap Layer Properties Dialog - Symbology Tab

The Symbology tab of the Layer Properties dialog is where you specify layer symbology.

Access Location:

ArcMap

Table of Contents: Right-click a layer > Properties. Click the Symbology tab.

Table of Contents: Click the symbol in the table of contents.

Figure 6: Symbology Tab

Symbology Tab Options

Show

Allows you to choose the display method for the image.

Import

Launches the import dialog and allows you to choose an image to import.

Display Background Value (R, G, B)

When selected, displays the background value of the image.

as

Displays RGB values as specified.

Display NoData as

(22)

Stretch

Type

Allows you to choose the stretch type from a predefined list of options. For example, Custom, Standard Deviations, Histogram Equalize and Minimum- Maximum are available.

Histograms

Opens the Histogram for <layer> dialog for you to setting per band.

Invert

When selected, inverts the stretch applied to the image.

Apply Gamma Stretch

When selected, applies a gamma stretch to the image.

Statistics

(23)

(24)

LIDAR Analyst Toolbars

Many of the features and functions of the LIDAR Analyst application can be accessed from the LIDAR Analyst toolbars. The standard (default) toolbar includes a drop-down menu, and opens with the most commonly used tools and shortcut tool buttons.

LIDAR Analyst includes the following toolbars: LIDAR Analyst Toolbar

LIDAR Analyst Bare Earth Toolbar LIDAR Analyst Building Edit Toolbar

In This Section

LIDAR Analyst Toolbar ... 19 LIDAR Analyst Bare Earth Toolbar ... 19 LIDAR Analyst Building Edit Toolbar ... 20

LIDAR Analyst Toolbar

The standard LIDAR Analyst toolbars open, by default, with the most commonly used tools. You can add or remove tool buttons to suit your needs.

Figure 7: LIDAR Analyst Toolbar

LIDAR Analyst Bare Earth Toolbar

The Barth Earth toolbar provides tools for adding data points, removing ground clutter such as trees and buildings, reassigning, raising or lowering DEM heights, as well as replacing a DEM region.

(25)

LIDAR Analyst Building Edit Toolbar

The Building Edit toolbar provides tools for building settings, reshaping, cleanup, reorienting, squaring up, eroding, aggregating, smoothing features, and creating points in a building layer.

Figure 9: Building Edit Toolbar

Customizing a Toolbar

You can customize the LIDAR Analyst toolbar with any or all of the LIDAR Analyst tools, including shortcut tool buttons associated with menu commands.

Note: All <product _name> functions can be added as a tool button to the toolbar.

Adding Tools to a Toolbar

For your convenience, you have the option of customizing the toolbar with specific tools/commands.

To add tools to a toolbar:

1. Right-click on the LIDAR Analyst (on page 19) toolbar or click the drop arrow, then choose

Customize from the shortcut menu. The Customize dialog box opens.

Figure 10: Customize Dialog

(26)

LIDAR Analyst 5.1.x Tutorial | 21 LIDAR Analyst Tools and the ArcMap Interface 3. Select one of the following in the Commands list box:

LIDAR Analyst Commands LIDAR Analyst Tools Overwatch Commands Overwatch Tools

4. Select the tool you want to add to the toolbar from the Commands list box.

5. Click and drag the tool to the LIDAR Analyst toolbar. Release the tool on the toolbar where you want it to appear. The tool appears on the toolbar in the location where you placed it.

6. Continue to drag and drop tools on the toolbar, as necessary.

7. To save your customized toolbar for use with the current project only, select the Options tab of the Customize dialog. The Options tab displays.

Figure 11: Options Tab

8. Select Save all customizations to the document. The Save in Document dialog displays. 9. Choose OK to save the customizations to the current document.

10. To save the change to the base (normal.mxt) template, uncheck the Save all customizations

to the document check box. This displays your customized toolbar in every new project you

open. 11. Click Close.

(27)

Removing a Tool from a Toolbar

It is easy to remove any tool or command from a toolbar. The Customize dialog must be opened first before you can remove a tool.

To remove a tool from a toolbar:

1. Do either of the following to open the Customize dialog:

Right-click on the LIDAR Analyst toolbar and select Customize on the shortcut menu. Click the drop-down arrow on the toolbar and select Customize on the shortcut menu. The Customize (on page 166) dialog displays. All buttons on the toolbar activate.

2. Do one of the following:

Left-click the tool and select Delete from the shortcut menu.

Figure 12: Tool Shortcut Menu

Drag the tool off the toolbar and release the mouse.

Resetting a Toolbar

The toolbar settings can be reset to their default. You must open the Customize dialog to reset a toolbar.

To reset the LIDAR Analyst toolbar:

1. Do either of the following to open the Customize dialog:

Right-click on the LIDAR Analyst toolbar and select Customize on the shortcut menu. Click the drop-down arrow on the toolbar and select Customize on the shortcut menu. The Customize dialog displays.

2. Select the Toolbars tab. The Toolbar tab displays.

3. Select the appropriate toolbar in the Toolbars list, and click Reset. The toolbar resets to its default setting.

(28)

Edit Mode in ArcMap

When a new feature class is created, it is automatically placed in edit mode. However, if you want to return to that file later and make changes, you need to enable Edit mode in ArcMap.

Manually Starting Edit Mode

You can manually start the edit mode should you need to work with a feature class. To manually start feature class editing:

1. Highlight the feature class or object you wish to edit in the ArcMap table of contents (on page 13).

From the ArcMap Editor (on page 24) toolbar, select Editor > Start Editing. The tools needed for a basic LIDAR Analyst workflow are enabled on the LIDAR Analyst Bare Earth toolbar. The ArcMap Editor tools are enabled.

2. Select the Target drop-down arrow on the ArcMap Editing (on page 24) toolbar to select the feature class. The LIDAR Analyst Bare Earth (on page 19) toolbar is now enabled.

LIDAR Analyst applies the data frame’s spatial referencing to the new shapefile. 3. Make applicable edits.

Saving Edits and Stopping the Editing Process

When you are done editing a feature class, you can save your edits and end the editing session. To save edits and stop editing options:

1. From the ArcMap Editor (on page 24) toolbar, select Editor > Save Edits from the drop-down menu. The edits are saved.

(29)

ArcMap Editor Toolbar

The ArcMap Editing toolbar is frequently used to start and stop editing mode when working with features and graphics. Refer to the ArcMap documentation for information about these tools.

ArcMap 10 and 10.1

Toolbar: Editor

(30)

Chapter 4

Beginning Lesson

In This Chapter

Beginner Lesson ... 25

Beginner Lesson

LIDAR Analyst radically simplifies the process of extracting 3D features (bare earth surfaces, buildings, and trees), while providing tools for DEM editing, hillshading and relief, building squaring, and data attribution for buildings, tree points, and forest polygons.

The LIDAR Analyst Tutorial introduces you to the basic concepts and features of the LIDAR Analyst software and is the first step in learning to use LIDAR Analyst to extract 3D features. You can jump right into 3D feature extraction by using the LIDAR Analyst Tutorial dataset and

documentation to guide you through basic bare earth extraction, extracting buildings, forests, and trees, and classifying the point cloud data. Using the LIDAR Analyst Tutorial, you can review the provided extraction results, run the data using the Tutorial lessons, and then experiment with the software using the provided dataset.

Overwatch would like to thank the National Oceanic and Atmospheric Administration (NOAA) and GeoICT (Geospatial Information and

Communication Technology Lab)/Optech Incorporated for their permission to use these images in the development of our LIDAR Analyst tutorial.

(31)

26 | Beginning Lesson Chapter 4

Basic Workflow

An established workflow enables you to streamline the work and focus on results. The LIDAR Analyst project workflow is a specific sequence of process steps designed to produce good results and improve efficiency and productivity.

Figure 14: LIDAR Analyst Workflow

Basic Setup and Preparation

Before starting the first Tutorial lesson, it is important to set up a project results folder and save a working copy of the Tutorial project.

(32)

LIDAR Analyst 5.1.x Tutorial | 27 Beginner Lesson

Create a Project Results Folder

Before you begin running the LIDAR Analyst Tutorial, it is important to set up a tutorial results folder on your local (C:\) drive. The tutorial results folder will serve as the designated location to output results generated from the Tutorial lessons and data to keep results organized and separate from the original dataset.

Figure 15: Sample LIDAR Analyst Results Folder Setup

Naming Results

Although it is normally recommended that you use the automatic default naming convention assigned by LIDAR Analyst when saving files (a name based on the name of the image and the process and including incremental numbering to identify multiple versions), it is important to use a different file naming convention when saving the files generated in the LIDAR Analyst Tutorial. Since you will be generating a second set of result files for the Tutorial lessons, it is important to name your files in a way to keep them separate from the results provided.

The LIDAR Analyst Tutorial Project results are named as follows: TO_Core_last_DEM_AR.tif TO_Core_last_DEM_AR_bareEarth.tif TO_Core_last_DEM_AR_bareEarth_hillShade.tif TO_Core_last_DEM_AR_bareEarth_ground_mask_modlayer TO_Core_last_DEM_AR_bareEarth1.tif TO_Core_last_DEM_AR_bareEarth_hillShade1.tif

Name your Tutorial results to include part of the data name, the process, and incremental numbering as necessary. For example:

TO_Core_last_DEM_AR.tif (provided) FR_bareEarth.tif FR_bareEarth_hillShade.tif FR_bareEarth_ground_mask_modlayer FR_bareEarth1.tif FR_bareEarth_hillShade1.tif

(33)

Good file organization will enable you to easily distinguish between the provided results and the results you generate.

Opening the Tutorial Project

The LIDAR Analyst Tutorial includes two lessons. When you open the LIDAR Analyst Tutorial, all the data and results for Lesson 1 and Lesson 2 are loaded for you in the table of contents. You will begin the Tutorial by using the data provided. After you run each process, you can compare your results easily with the Tutorial results provided.

You can exit the Tutorial at any time and return later to complete it. Simply, save your changes before exiting the application. The beginning lesson of the LIDAR Analyst Tutorial provides the basic concepts and workflow, while the second lesson covers the more advanced features of the application.

To open the tutorial project: 1. If needed, open ArcMap.

2. From the LIDAR Analyst (on page 19) toolbar, choose LIDAR Analyst > Help > Tutorial > LA

Tutorial Project. The LIDAR Analyst Tutorial Project opens in a second instance of ArcMap.

The Tutorial image and final result layers display in the workspace.

Saving Your Tutorial Project

When working in the LIDAR Analyst Tutorial, you should save your work periodically. To save the tutorial project:

1. Select File > Save As on the ArcMap menu bar. The Save As dialog displays.

2. Navigate to C:\My_LA_Tutorial_Results\Lesson 1, enter a new name for your tutorial project file.

3. Click Save. The project is saved.

Opening Your Saved Tutorial Project

You can open a previously saved tutorial project. To open your saved project:

1. Select File > Open on the ArcMap menu bar. The Open dialog displays.

2. Navigate to C:\My_LA_Tutorial_Results\Lesson 1, select your tutorial .mxd file. 3. Click Open. Your saved tutorial project opens.

(34)

Lesson 1: Basic LIDAR Extraction

In this first lesson, you will use the LIDAR Analyst default settings to familiarize yourself with LIDAR Analyst and quickly run through a basic extraction workflow. The basic workflow includes extracting bare earth, extracting buildings, and then extracting trees.

To begin, you will create a hillshaded DEM to improve visualization of your images. Next, you will extract bare earth from your pre-loaded first and last return DEMs. A bare earth layer essentially represents the ground surface as it would appear without high vegetation or man-made objects. Bare earth is like a DEM minus buildings, trees, and other large features.

The bare earth DEM is created by identifying ground regions, extracting points from these regions, and then interpolating a ground surface from these points. Ground regions are identified using slope, aspect, and other parameters.

With a good bare earth layer, you can then extract buildings. Buildings are one of the most important geospatial features for spatial analysis and mapping. Buildings are represented as red-outlined polygons. The buildings layer is a polygon shapefile, not a raster image. After generating the building layer, you will extract trees and forested areas.

(35)

Opening the Tutorial Project

The LIDAR Analyst Tutorial includes two lessons. When you open the LIDAR Analyst Tutorial, all the data and results for Lesson 1 and Lesson 2 are loaded for you in the table of contents. You will begin the Tutorial by using the data provided. After you run each process, you can compare your results easily with the Tutorial results provided.

You can exit the Tutorial at any time and return later to complete it. Simply, save your changes before exiting the application. The beginning lesson of the LIDAR Analyst Tutorial provides the basic concepts and workflow, while the second lesson covers the more advanced features of the application.

To open the tutorial project: 1. If needed, open ArcMap.

2. From the LIDAR Analyst (on page 19) toolbar, choose LIDAR Analyst > Help > Tutorial > LA

Tutorial Project. The LIDAR Analyst Tutorial Project opens in a second instance of ArcMap.

(36)

Creating a Hillshaded DEM

Hillshading allows you to add three-band (RGB), color-shading effects (values from 0 to 255) to aid in visualizing the features in the bare earth layer. Relief adds shadows and texture to the output image. These effects create a pseudo-3D image, which gives you clues (such as shadow and variations in lighting) about the elevation of the terrain. Hillshading the first-return DEM assists in visualizing buildings and other features with elevation values.

To create a hillshaded DEM:

1. Select the firstreturn_1m_dem.tif layer for display. The first return DEM displays in the workspace.

Figure 17: First and Second Return

2. From the LIDAR Analyst (on page 19) toolbar, do either of the following: Click the Create Hill-Shade Image button .

Select LIDAR Analyst > Analysis > Create Hill-Shaded Image. The Hill-Shade and Relief (on page 60) dialog opens.

3. Under Shading Style, select Elevation #1.

4. Accept the default settings for the other options and click OK. The Save Raster Data dialog opens.

(37)

By default, LIDAR Analyst names the image in the Name field using the name of the first return image and the process (in this case, hillShade).

(38)

Bare Earth Extraction

The first step in a basic LIDAR extraction is to generate the bare earth surface. The bare earth extraction removes ground clutter, such as trees, buildings, cars, and other above ground objects to delineate the digital elevation model (DEM) or bare earth (BE) to best represent the topography. You can complete bare earth extractions using either both first and last return data or a single return only. You can use either a raster image or an LAS file as the input. In this lesson, you will extract bare earth using first and last return DEMs. Using both first and last return LIDAR data usually enables the best bare earth results.

Prerequisites:

Ensure you have setup your project results folder and save a copy of the tutorial as described in Lesson 1.

To complete a bare earth extraction:

1. If necessary, right-click on the Exercise 1 data frame in the table of contents (on page 13) and select Activate. The data frame name, Exercise 1, displays in bold letters.

2. Select the firstreturn_1m_dem and the secondreturn_1m_dem layers for display. Deselect all other layers. The first and second return DEMs displays in the workspace.

Figure 19: First and Second Return

3. From the LIDAR Analyst (on page 19) toolbar, do either of the following: Click the Extract Bare Earth button .

(39)

The Bare Earth Extraction (on page 48) dialog displays.

Figure 20: Bare Earth Extraction

4. Under Bare Earth Extraction Methods group box, select Method 1: Raster or Point Clouds. 5. Select the secondreturn_1m_dem.tif from the Single/Last Return drop-down menu.

6. Select the firstreturn_1m_dem.tif from the First Return drop-down menu. You may need to expand the dialog to see these options.

7. Under Map Units group box, select Horizontal units and Vertical units.

8. Accept the settings under Pre-process and Post-process. For detailed information about these options, see Bare Earth Extraction (on page 48) reference topic.

Note: A pre-process option runs on the input DEMs, while a post-process option refers to the

(40)

LIDAR Analyst 5.1.x Tutorial | 35 Beginner Lesson 9. Click the More button on the Bare Earth Extraction dialog. The dialog expands (on page 51) to

show more options.

Figure 21: Bare Earth Expanded

10. Under Tree and Forest Parameters, deselect the Use average slope for tree mask check box.

11. Accept the remaining settings. The default extraction settings work for the majority of LIDAR extractions.

12. Click the Bare earth output [...] button ((bottom left-side) on the Bare Earth Extraction (on page 48) dialog. The Save Raster Data dialog displays. By default, LIDAR Analyst names the image in the Name field using the name of the last

13. Navigate to C:\My_LA_Tutorial_Results\Lesson 1 and name the file, bareEarth.tif.

Note: To complete this step, you need to complete the first tutorial on setting up project results

folder and save a working copy of the tutorial.

14. Click the Save button on the Save Raster Data dialog to save the file. The bare earth output displays in the Bare Earth Output field on the Bare Earth Extraction dialog.

(41)

The LIDAR Analyst extraction progress window display showing the extraction progress. When the bare earth extraction is complete, the bare earth result file appears in the table of contents and displays in the workspace.

Figure 22: Bare Earth

LIDAR Analyst displays a message box asking if you want to generate a hillshade image for 'bareEarth.tif'.

16. Click Yes to create a hillshade. The Hill-Shade and Relief (on page 60) dialog displays. You are now ready to continue to the next topic - Generating a Hillshade Layer (on page 37).

(42)

Generating a Hillshade Layer

Hillshading allows you to add three-band (RGB), color-shading effects (values from 0 to 255) to aid in visualizing the features in the bare earth layer. Relief adds shadows and texture to the output image. These effects create a pseudo-3D image, which gives you clues (such as shadow and variations in lighting) about the elevation of the terrain.

To generate a Hillshade layer:

1. If needed, complete the previous Bare Earth Extraction tutorial topic and ensure the Hillshade

and Relief (on page 60) is displayed.

Figure 23: Hill-Shade and Relief

2. Set the following in the Hillshade and Relief dialog:

Accept the default settings for Lighting Altitude (45) and Lighting Azimuth (315). See

Hillshade and Relief (on page 60) reference topic for other input options.

Deselect the Compute Shadow option.

Select Bare earth in the Shade Style group box. Click OK.

The Save Raster Data dialog displays.

LIDAR Analyst names the image in the Name field using the name of the bareEarth image and the process (in this case, hillShade).

3. Review the default file name (bareEarth_hillShade.tif) and location

(C:\My_LA_Tutorial_Results\Lesson 1) for the bare earth, hillshade layer.

4. Click the Save button. The LIDAR Analyst progress window opens, displaying the progress of the hillshade layer.

(43)

The bare earth, hillshade layer displays in the table of contents and in the workspace.

Figure 24: Bare Earth Hillshade Layer

Examining Bare Earth Results

The bare earth extraction process strips the image to the earth terrain. The shading shows the elevation changes within the image area.

Examine the bare earth layer. It should appear relatively smooth and topographically uniform with no raised features or distortion clearly visible.

The next step in most LIDAR extractions is to clean up any anomalies or false positives in the bare earth layer.

Note: Hillshaded DEMs are useful for reviewing building result accuracy.

LIDAR Analyst provides a series of tools designed to quickly clean up your bare earth results. In Lesson 2, you will find more information on the Bare Earth Modification tools and how to use them to get the best results from your bare earth layers.

(44)

Building Extraction

Once you have created a good bare earth layer, you can use LIDAR Analyst to extract buildings. To extract buildings, LIDAR Analyst detects and isolates points in specific areas of an image that are within the set building parameters. The resulting buildings layer is a 3D shapefile (not a raster image) from which a 3-D building model can be displayed.

To extract buildings:

1. From the LIDAR Analyst (on page 19) toolbar, do either of the following: Click the Extract Buildings button .

Select LIDAR Analyst > Extraction > Extract Buildings. The Building Extraction (on page 57) dialog displays.

When applicable, LIDAR Analyst detects and enters your bare earth layer in the bare earth field.

2. Verify that your bare Earth layer displays in the Bare earth field. If necessary, select the correct bare earth layer.

The last return LIDAR image and first return LIDAR image appear in their respective fields. The Horizontal and Vertical Units selected for the bare earth extraction display under Map Units.

3. Click the Reset to Defaults. All settings reset to the default values.

Note: Since the system retains the settings from the last extraction. Resetting the defaults

each time you run an extraction ensures control over all the current settings.

4. Enter the following custom parameters in the center of the Building Extraction dialog. You may need to expand the dialog to show options.

Remove Buildings with area less than field: 5 square meters. Remove Buildings with height less than field: 3 meters. Texture variance for trees field: 50 percent.

Min difference between returns for trees: 0.1 meters. Accept the default settings for the remaining options.

For additional input options, see the Building Extraction (on page 57) reference topic. 5. Click the Square-up options button or click the Square Up tab. The Building Square-Up

Settings (on page 59) dialog/options displays.

6. Accept the other default settings under Building Square-Up Settings. For additional parameters, see the Building Square-Up reference topic.

7. Click OK.

8. Accept the default parameters under Extract tall buildings. For additional parameters, see the

Building Square-Up Settings (on page 59) reference topic.

9. Click the Ellipsis [...] button next to the Building output field. The Save Feature Data dialog displays. LIDAR Analyst suggests a name based on the name of the last return and the process (in this case, buildings).

10. Navigate to C:\My_LA_Tutorial_Results\Lesson 1 and name the file buildings.shp. 11. Click Save. The Buildings layer filename appears in the Building output field.

(45)

12. Click OK on the Building Extraction (on page 57) dialog. The progress window opens, displaying the progress of the building extraction. When the building extraction is complete, the buildings extraction layer appears in the table of contents and in the active workspace.

(46)

Viewing the Attribute Table

Without having ArcScene, ArcGlobe or Overwatch's new 3D viewer, you can view the 3D attributes for your building polygons by opening the Attribute Table from the ArcMap table of contents.

To view the attribute table from ArcMap:

1. Right-click any building layer in the table of contents (on page 13).

2. Select Open Attribute Table. The Attribute Table displays. Notice the Height columns. These show the Z-values for each polygon.

Figure 26: Attribute Table

(47)

Tree Extraction

After generating a satisfactory building layer, the next step is to extract the trees and/or forested areas. Extracting the vegetation in your dataset completes the LIDAR Analyst extraction process. To extract vegetation, LIDAR Analyst detects and isolates points in specific areas of an image. The resulting trees layer is a 3D shapefile (not a raster image).

To extract trees:

1. If needed, complete the Building Extractions.

From the LIDAR Analyst (on page 19) toolbar, do either of the following: Click the Extract Trees button .

Select LIDAR Analyst > Extraction > Extract Trees.

The Tree Extraction (on page 62) dialog displays. When applicable, LIDAR Analyst enters the bare earth layer in the bare earth field.

Figure 27: Tree Extraction

2. In the Tree Extraction dialog do the following:

Verify that your bare earth layer displays in the bare earth field. If necessary, select the correct bare earth layer. The last return LIDAR image, and the first return LIDAR image if used, appear in the respective fields.

Verify that your buildings layer displays in the Buildings field. If necessary, select the correct buildings layer. The Horizontal and Vertical Units selected for the bare earth extraction display under Map units.

(48)

LIDAR Analyst 5.1.x Tutorial | 43 Beginner Lesson 3. Under Extraction Method, select Method 2: Variable window search (better at getting

accurate crown widths). For more information, see Tree Extraction (on page 62) reference

topic.

4. Under Output Files, select the Tree Points option. The Save Feature Data dialog displays. LIDAR Analyst suggests a name based on the name of the last return and the process (in this case, trees).

5. Navigate to C:\My_LA_Tutorial_Results\Lesson 1 and name the file trees.shp. 6. Click Save. The Tree Extraction dialog is now active.

7. Ensure the following default settings are specified: Predominant tree forest/forest type: Mixed Minimum tree height: 3 meters

Maximum tree height: 40 meters

For additional options, see Tree Extraction (on page 62) reference topic.

8. Click OK. The LIDAR Analyst extraction process dialog displays showing the extraction process. When the extraction completes, LIDAR Analyst places the new layer in the active workspace. Each individual tree is represented by a yellow point.

(49)

Forest Extraction

Using the same image, you can extract stands of trees or forests, rather than individual trees. Follow the instructions below to generate different tree extraction results.

Note: Although run separately here, you can run the tree and forest extractions at the same time

and the extraction process will return two layers simultaneously. To extract a forest:

1. From the LIDAR Analyst (on page 19) toolbar, do either of the following: Click the Extract Trees button .

Select LIDAR Analyst > Extraction > Extract Trees.

The Tree Extraction (on page 62) dialog displays. When applicable, LIDAR Analyst enters the bare earth layer in the bare earth field.

2. Verify that your bare Earth layer displays in the bare earth field. If necessary, select the correct bare earth layer.

The last return LIDAR image and the first return LIDAR image appear in the respective fields. When applicable, LIDAR Analyst automatically enters the building layer in the Buildings field. 3. Verify that your buildings layer displays in the Buildings field. If necessary, select the correct

buildings layer.

The Horizontal and Vertical Units selected for the bare earth extraction display under Map units.

4. Click the Reset to Defaults button on the Tree Extraction (on page 62) dialog.

5. Under Extraction Method, select Method 2: Variable window search (better at getting

accurate crown widths).

6. Under Output Files at the bottom of the dialog box, deselect Tree Points and select Forest

Areas. The forest parameters in the center of the dialog box become available.

The Save Feature dialog displays.

7. Type a name and click Save. The file name appears in the Forest Areas field under Output Files.

8. Ensure the following default settings are specified: Predominant tree forest/forest type: Mixed Minimum tree height field: 3 meters Minimum size of a forest field: 600 meters

See the Tree Extraction (on page 62) reference topic for more information about forest parameters.

9. Click OK. The LIDAR Analyst progress window opens, displaying the progress of the forests extraction.

When the forest extraction is complete, the forests extraction layer appears in the table of contents and in the active workspace.

(50)

Figure 29: Forest Extraction

Each forest area is represented by a polygon.

Notice that the forest areas do not include all stands of trees.

Trees not included in forest results did not meet the set criteria for stands greater than 600 meters.

Note: To get a better view of the forest layer, turn off the trees layer.

10. Save tutorial project.

(51)

(52)

Reference: Lesson 1

In This Section

Bare Earth Extraction Dialog ... 48 Bare Earth Modification Settings Dialog ... 55 Building Extraction Dialog ... 57 Square-Up Tab (Formerly) Dialog - Building Extraction Dialog .... 59 Hill-Shade and Relief Dialog ... 60 Overwatch Progress Window ... 61 Tree Extraction Dialog ... 62

(53)

Bare Earth Extraction Dialog

The Bare Earth Extraction dialog is used to create and configure bare earth settings. You can specify returns, map units, extraction, as well as pre and post processing options.

LIDAR Analyst

Menu (LIDAR Analyst Toolbar): LIDAR Analyst > Extraction

Toolbar: LIDAR Analyst

Command: Extract Bare Earth

Doc Id: 9806

Figure 30: Bare Earth Extraction

Bare Earth Extraction Dialog

Single/last return

Select a single/last return file from the drop-down menu or launch the LAS File Selector dialog.

First return

(54)

Map Units

Horizontal units

Allows you to choose the horizontal units for the bare earth extraction including Unknown, Inches, Feet, Miles, Centimeters, Meters, Kilometers, Decimal Degrees, Minutes, Seconds, and Radians.

Vertical units

Allows you to choose the vertical units for the bare earth extraction including Unknown, Inches, Feet, Miles, Centimeters, Meters, and Kilometers.

Output Resolution (Point clouds only)

Manually specify cell size

If extracting bare earth from LIDAR point clouds, choose this option to manually specify the cell size of the output bare earth in map units. You should select this option if you already know the native point spacing of the input point clouds or if you want to output a bare earth at a different resolution than the point spacing of your input point clouds.

Estimate Cell Size

If extracting bare earth from LIDAR point clouds, choose this option to allow LIDAR Analyst to automatically detect the point spacing of the LIDAR point clouds. This information is used by LIDAR Analyst to set the cell size of the output bare earth raster.

Bare Earth Extraction Method

Method 1: Rasters or Point Clouds

Select this option to find ground points that are not close to non-ground objects, such as buildings and trees.

Method 2: Point Clouds

Select this option for extracting bare earth from LAS point clouds. This option works well on just about any LAS point cloud but especially well on dense forests. Selected by default.

Use existing ground points are used if this option is checked.

Pre-process

Auto-detect no-data regions

Large, flat areas of 100 square meters or more that are filled with a single value or no value are considered "no-data" regions. Bodies of water, which produce inaccurate LIDAR values, are typical of such resulting features. Selecting this option enables a search for no-data regions in the DEMs and removes such regions from the list of regions that will be processed for bare earth. Since large, perfectly flat regions do not occur naturally, selecting this option will produce better results. The option is selected by default.

Remove spikes and pits before processing

Selecting this option enables the search and removal of spikes and pits caused by anomalies in the input DEMs. Use this option only if the LIDAR data was not cleaned by the vendor. It is better to run this process as a separate, post-processing option, where you have more control over the removal parameters. By default, this option is not selected.

Note: If you know that your data does not have any large flat regions, clear this option to speed up

(55)

Post-process

Remove negative nDSM regions

Since the extracted bare earth layer is an estimate of the bare-ground with features removed, it can lead to a normalized Digital Surface Model (nDSM) with negative values. The negative nDSM value corresponds to an area where the extractor estimated the bare earth surface to be higher than the actual surface height. These regions can therefore be safely set to the actual DEM height. A flattened DEM model is obtained using the formula: nDSM = DEM – bare earth.

Selecting this option results in all nDSM regions being replaced with last-return DEM values, thus setting those regions to an nDSM value of zero. If, after running a preliminary bare earth

extraction, you find large height variations in your bare earth, you can try selecting this option and running your bare earth extraction again. By default, this option is not selected.

Smooth bare earth using low-pass filter; removes cars, shrubs, and low height objects

Selecting this option runs a Low-Pass Filter (LPF) on the extracted bare earth. Through a

smoothing effect, the LPF removes the appearance of cars, shrubs, and low objects from the bare earth. By default, this option is not selected.

Bare earth output

Displays the output location for the bare earth extraction.

Reset to defaults

Resets all bare earth extractions to the default settings.

More

Expands the dialog to include more advanced bare earth extraction options.

Run Visible Extent

Runs as specified.

Preview

(56)

Bare Earth Extraction (Expanded Method 1) Dialog

The Bare Earth Extraction dialog expands to show additional options.

Figure 31: Bare Earth Extraction Expanded

Bare Earth Extraction (Expanded) Options

Tree and Forest Parameters (Method 1)

Minimum slope for tree regions

Regions of the DEM with a slope greater than this value will be considered tree regions. The default is 10 degrees.

Minimum texture for tree regions

Regions of the DEM with a texture greater than this value will be considered tree regions. Texture values are derived from the aspect of the last-return DEM. The default is 80 percent.

Minimum difference between returns for tree regions

Any pixel where the elevation difference between first and last returns is greater than this value will be considered a tree region. Note: Use only when you are processing both first-and last-return data. The default is 0.3 meters.

Minimum forest size

Tree regions with an area greater than this value will be considered forest. The default is 10,000 square meters.

Sample 1 point in forest regions for every <value>

In forested areas, a ground point (an interpolation point) will be sampled from the lowest elevation value that occurs in a square of the defined area.

(57)

Use average slope for tree mask

Check this option with bare earth extraction method 1 selected to perform LIDAR Analyst’s 4.2 method 1 extraction. Uncheck this option with bare earth extraction method 1 selected to perform LIDAR Analyst’s 4.2 method 2 extraction.

Ground Parameters (Method 1)

Slope threshold for flat ground (maximum slope in flat/steep ground)

Regions with a rate of change in slope lower than the slope threshold for flat ground will be considered flat ground, as opposed to steep ground. Thresholds are used to classify the maximum slope in flat ground and the maximum slope in steep ground as ground. The default slope

threshold is 78 degrees. The default maximum slope in flat ground is 55 degrees and the default maximum slope in steep ground is 10 degrees.

Maximum slope in flat ground

Regions with a rate of change in slope lower than the slope threshold for flat ground will be considered flat ground, as opposed to steep ground. Thresholds are used to classify the maximum slope in flat ground and the maximum slope in steep ground as ground. The default slope

Maximum slope in steep ground

Regions with a rate of change in slope greater than the slope threshold for flat ground will be considered steep ground, as opposed to flat ground. Thresholds are used to classify the maximum slope in flat ground and the maximum slope in steep ground as ground. The default slope

Minimum area for ground regions

Defines the minimum area of a ground region. Does not determine the minimum polygon size in the final ground mask. The default is 35,000 square meters.

Sample 1 point in ground regions for every <value> (Method 1 and Method 2)

Defines the sampling rate of ground points. At least one ground point will be extracted for each window of this size within the ground regions. The default is 9 square meters.

Output last return if elevation difference between last return and ground surface estimate is (Method 1 and Method 2)

If the distance between the last-return (or single return) DEM and the extracted bare earth is lower than this threshold, then that region will be replaced with values from the last-return DEM. This step adds fidelity to the extracted bare earth. If this value is set to 0, then the output bare earth will be the original interpolated bare earth with post-processing clean-up applied. The default is 0.5 meters.

Return Parameters (Method 1)

Threshold difference between last return and ground surface estimate to ground mask

Defines the distance between the bare earth and the last-return (or single return) DEM. Regions with a distance lower than this threshold will be considered ground regions. The default is 0.1 meters.