LAS Point Classifications

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)

  • 32 codes shown to the left.  The names for display codes are stored in "LAS_codes_v2.dbf" in the main program directory.  Few LAS files actually use the Building category, or multiple vegetation categories.
  • 28 bytes per elevation point
  • Up to 5 returns per pulse

 

 

Version 1.4

  • will require a major revision of the MICRODEM code, and I have yet to see a file using the new codes (or even the 1.4 version of the format)
  • up to 15 returns per pulse
  • 30 bytes per elevation point
  • 256 classes. 
    • Classes 10-16 will be new, for rails, roads, bridges, and power transmission lines (4 categories) reflecting the use of LIDAR to monitor these features.
    • Classes 8 and 12 are reserved, as there are now new ways to show model key points and overlap points.
    • User defined start at 64

 


Lidar Point cloud viewers and tools

Lidar Point Cloud Data Sources


last revision 11/14/2017