Finding Tree Tops
- Use raster calculator to remove values less than 25 meters from the CHM.
- Run a lowpass filter (alternatively, focal statistics 3×3 rectangle/calculate mean) on the >25m masked CHM. This step helps to eliminate individual canopies having two or more “tops” identified erroneously. The output will have a greater extent than the input by ½ the focal stats window width x pixel width, which extends it into internal voids created by the >25m mask.
- Mask the lowpass output with the CHM >25 raster to restrict it to the original extent. Alternatively: specify output extent in the environmental variables in the lowpass geoprocessing tool.
- Use the focal statistics tool to identify local maxima—3×3 rectangular window, calculate maximum.
Use the raster calculator to identify treetops– pixels where the value of the focal stats 3×3 max raster equals the lowpassed raster (i.e. focal stats output == focal stats input). My expression looked like this:
Con(“CHM_GT25_LOWPASS_MASK”==”CHM_GT25_LOWPASS_MASK_MAX3x3”, “CHM_GT25_LOWPASS_MASK”).
