spelger

wow, read this from that page...

Is there a difference between 3D Elevation Program (3DEP) DEM data and lidar data?

Yes, lidar data are represented as a cloud of variably spaced point locations (x,y,z) of any terrestrial target reflecting the laser pulse. In addition to bare-earth, the point cloud will typically include buildings, trees, towers, and powerlines. 3DEP DEMs are raster surfaces of bare-earth elevation values sampled at uniform horizontal increments...

so, once you go under a tree or bridge your elevation may suddenly increase.

it is all interesting stuff but what amazes me most though is that it is 2020 and we still really don't have very accurate elevation everywhere that is easily available. last week i was using the USGS API to pull elevation data from a route i routinely ride, boy was it crappy. there were grades of over 30% and the most that hill has is maybe 8%.