Point Classification (ground, water, vegetation, building, power lines). While similar in concept to the Supervised and Unsupervised classification for satellite imagery, for LIDAR the classification relies on the geometric position of the return relative to its neighbors, and the first/last return category (if there are multiple returns for a single pulse, only the last could be on the ground). Classification can be a processing intensive operation, and many LIDAR data sets have undergone limited classification. Ground is almost always included in a LAS file, as it is needed to create a DTM. The commonly used versions of the LAS format (1.2 and 1.3) has 8 classification categories pre-defined and can handle up to 32; the newer version (1.4), which has still not been widely used, has about 20 predefned classes and can handle 256.
Ground classification is almost always included in a LAS files from national mapping agencies, as it is needed to create a DTM.
The LAS format includes point classifications. They are not always fully filled out, although many data sets have only moderate classification done. The new version of the format adds (1.4) another half dozen categories, primarily for electric transmission lines, but is still not very common.
LAS specification (version 1.3)
Lidar Point cloud viewers and tools
Lidar Point Cloud Data Sources
last revision 11/14/2017