[pdal] USGS 3DEP point classification

[Howard Butler]

> On Jun 13, 2022, at 12:37 PM, Andreas Yankopolus <andreas at yank.to> wrote:
> 
> I’m trying to get a sense of how point classifications get assigned with USGS 3DEP LAZ files.
> 
> I’m seeing the following looking at tiles for around Denver, Colorado:
> 
> 	• 1 (unclassified): usually maps to foliage/structures but also water.
> 	• 2 (ground): usually maps to bare earth, roads, etc.
> 	• 9 (water): maps to water.
> 	• 7 (low point) and 11 (road surface) generally map to spurious atmospheric returns
> 	• 17 (bridge deck) generally maps to surface features and 18 (high noise) to bare earth, but only within limited scan lanes. These two puzzle me.
> 
> Anyone know how these classifications are supposed to map out?

They should map according to the ASPRS LAS specification, and additionally, the USGS LiDAR Base Specification

https://www.usgs.gov/ngp-standards-and-specifications/lidar-base-specification-online

Howard