Normalize a Lidar LAS file with Fusion ClipData

There are occasions when it is necessary to normalise a LiDAR las point cloud file, i.e. removing the terrain heights. This can be useful if you are interested in the heights of objects e.g. vegetation canopy above the ground and not the undulations of the terrain below. An example of a las file point cloud is shown below; the shape of the terrain is very much evident.


The ClipData utility from the open source Fusion software can be used to normalise a LiDAR point cloud. The following steps illustrate how to normalise a point cloud.

1. In a Command Prompt, type in the following to convert a digital terrain model DTM from ESRI Ascii ArcGrid to Fusion's DTM format, using the ASCII2DTM.exe utility.
   
   C:\> ascii2dtm.exe output.dtm m m 0 0 0 0 input_dem.asc
   
   An example run is shown below.
   
   
2. At the prompt, type in the following.
   
   C:\> clipdata.exe /height /dtm:dakota_dem.dtm dakota.las output.las 606034 4889354 607400 4890580
   
   Note:
   /height tells the utility to normalise the point cloud
   /dtm:dakota_dem.dtm specifies the input digital terrain in Fusion's DTM format.
   dakota.las is the input las file
   606034 is the minimum bounding x value
   4889354 is the minimum bounding y value
   607400 is the maximum bounding x value
   4890580 is the maximum bounding y value
   
   An example run is shown below:
   
   
   A screenshot showing the normalised point cloud. Notice the point cloud no longer undulates with the terrain.