Thinning LiDAR files with LASTools

Dense LiDAR files can take a while to open and process. Sometimes it is convenient to work with a less dense version of a LiDAR file, perhaps as a test of some processing idea. ‘Thinning’ is the process of discarding LiDAR data from a file, in order to generate a smaller, less detailed file.

The lasthin.exe tool is perfect for this task, but it is not free open source licensed. The free las2las.exe can be used to achieve a similar result.

• Open the Windows command prompt:Win + X then Command prompt
• Navigate to the project folder: CD C:\GossanHill
• We’ll work with these files:

29/03/2017  04:32 PM           946,176 las2las.exe
30/03/2017  08:45 PM     1,107,238,731 Merged12.las

• Enter a command like this: las2las -i Merged12.las -keep_every_nth 2 -o Merged12-Half.las
• las2las is the program to run
• The -i Merged12.las part represents the input file
• The -o Merged12-Hald.las is the name of the output file we want to create.
• -keep_every_nth 2 is the instruction only keep ever 2nd data point. You can change the number to suit your needs.
• The program runs for a little while, then you’ll see that a new file Merged12-Half.las has been created. It is roughly half the size of the input file.
• We can run the program again: las2las -i Merged12-Half.las -keep_every_nth 2 -o Merged12-Quarter.las
• And again: las2las -i Merged12-Quarter.las -keep_every_nth 2 -o Merged12-Eighth.las
• The results are a set of files with less data (and smaller sizes, and quicker processing times):

30/03/2017  08:45 PM     1,107,238,731 Merged12.las
30/03/2017  09:01 PM       553,619,819 Merged12-Half.las
30/03/2017  09:04 PM       276,810,363 Merged12-Quarter.las
30/03/2017  09:05 PM       138,405,635 Merged12-Eighth.las

This article is part of the Orienteering Mapping with LiDAR, Smartphones and Free Tools series.

Polite and constructive responses are always welcome.