The ArcMap Tools toolbar is frequently used for the Zoom tools. Refer to the ArcMap documentation for information about these tools.
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ArcMap Zoom Tools
The ArcMap Zoom tools are used to adjust features. The ArcMap editing keyboard shortcuts for zooming in (z), zooming out (x), and panning (c) are available when working with the ArcMap Create Features tool.
Figure 72: ArcMap Zoom Tools
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.
Access Location:
LIDAR Analyst
Menu (LIDAR Analyst Toolbar): LIDAR Analyst > Extraction
Toolbar: LIDAR Analyst
Command: Extract Bare Earth
Doc Id: 9806
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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
Select a first return file from the drop-down menu or launch the LAS File Selector dialog.
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.
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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
processing time.
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
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Bare Earth Extraction (Expanded Method 1) Dialog
The Bare Earth Extraction dialog expands to show additional options.
Figure 74: 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.
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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.
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
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 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
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.
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.
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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.
Cleanup bare-earth (post-process)
Selecting this option applies a "noise" filter to the bare earth. The noise filter removes small imperfections, resulting in a smoother looking bare earth. Use the slider bar to set smoothness parameters. The further to the right (Less smooth) the slider is moved, the lower the effect of the filter, the fewer regions to which the filter is applied, and the fewer imperfections that will be removed.
Setup Interpolator
Allows you to choose either Hierarchical Spline Interpolator of ArcGIS Spline Interpolator as the interpolation method.
Extraction Parameters (Method 2)
Max. building size (length)
The length of the largest building in the image. The default is 100 meters.
Max. height to jump for region growing
The maximum distance to jump in the Z direction for the region growing process. The region growing process extracts more ground points from the initial seed ground points. The higher the jump distance the more the number of points that are higher in elevation will be collected. The default is 0.35 meters.
Max. slope of ground regions
The maximum slope within the regions that were extracted as ground. Any regions with slope greater than the maximum slope will be filtered out. The default is 45 degrees.
Number of iterations for bare earth extractions
The number of iterations for the bare earth extraction to extract probable ground points. The default is 2.
Minimum area of extracted ground regions
The minimum area of extracted ground regions. Any regions smaller than this will be filtered out. The default is 30 square meters.
Interpolation
Hierarchical Spline Interpolator
The native interpolator in LIDAR Analyst is the Hierarchical Spline Interpolator.
ArcGIS Spline Interpolator
If you have ArcGIS Spatial Analyst installed and activated on your workstation, the additional interpolator, ArcGIS Spline Interpolator, appears in the list. The Hierarchical Spline Interpolator often works better on large datasets. However, you may need to experiment to see which option works better with your data.
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