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.
52 | Beginning Lesson Chapter 4
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.
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.
LIDAR Analyst 5.1.x Tutorial | 53 Beginner Lesson
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.
54 | Beginning Lesson Chapter 4