TIN DSM Algorithm used in LidR package R

Question

I have a question regarding to the TIN method used in LidR. My point cloud data is look like this figure. When I compute DSM using TIN method, the height value is not at the highest peak of first return. Does the value used in triangulation is an average value from several first return within one pixel? Is there any ways to retrieve the DSM from the highest first return using LidR or another software? Thank you.

• Michael -

I am expecting to retrieve clarification about the TIN algorithm used to generate DSM in LidR package.

Answer 1

lidR triangulates the first returns and interpolates at the location of the centers of the pixels. So if a pixel is at the center of a triangle the value it returns is a linear combination of the elevation of the 3 points of the corresponding triangle. In your example the pixels look very big. Consequently the center of the pixel is somewhere in one of the many triangles encompassed by the pixel. It'd say it is relatively meaningless to compute a triangulation-based CHM with a resolution much larger than the average point spacing.

If you want to make a CHM that correspond to the highest point use a point-to-raster based method i.e. p2r().