Canopy Height Model (CHM) is important for a variety of uses. The distinguishing factor of this model is that it is a height above ground model and does not represent absolute elevation. We can produce this model in LP360 with the following workflow that incorporates Point Cloud Tasks (PCTs) and the export function.
Note: the user will need to have vegetation and ground already classified. A combination of LP360 tools, including the Adaptive TIN Ground Filter and Height Filter PCTs, can be used to perform this classification. A 3D polygon feature must also be created to encompass the area of interest (AOI) of the desired CHM.
To begin, create a Volumetric Analysis Point Cloud Task and setup similar to the workflow below:
- Base: 3D Polygon Boundary: Tool Geometry/Shp Layer (boundary shape must be selected), Surface Generation Method: Use LAS Points, Source Points: Ground class
- Hull: 3D Polygon Boundary: Tool Geometry, Surface Generation Method: Use LAS Points, Source Points: Ground and High Vegetation classes
- Volume: The task needs a file output location for this tab, but we will not be using the output from this function.
- Cut/Fill: Leave blank.
- LAS Output: LAS Point Source: Hull, LAS Output Location: choose an appropriate location for output. This is the output needed for the CHM.
- Run the task by project.
The user now has 2 options for creating their CHM:
Classify by Statistics PCT: This task can classify the highest point for the designated cell size. The user will now have canopy points that have the appropriate height above ground values.
Export Wizard: This will allow the user to generate a CHM based on the LAS data export from the Volumetric Analysis PCT. Recommended settings:
Step 1
- Export Type: Surface
- Surface Method: IDW
- Surface Attribute to Export: Elevation
- Export Format: User choice
Step 2 and 3
User choice for these settings. Be sure to specify a proper output in Step 3.
Now the user will have a CHM for this dataset with height instead of elevation values.
