Splitting LiDAR point clouds

Discrete LiDAR

In the case of purely discrete point clouds we can use lasmerge to produce equal divided files.

A script exists to do this automatically:

split_las.py (-d INPUTDIR | -f INPUTFILE) [-o OVERLAP] outputdir fraction

This can be run on either a single file or a directory of las files.

Use -o to specify the number of seconds of overlap, this can be used with the airplanes ground speed to calculate overlap. For instance 7 seconds 140 knots will result in an overlap of 504 metres (7 seconds * 72 m/s). Give the script a fraction for the number of lines to divide the line into, I usually just give it 3.

Full Waveform

Full wave form data cannot use the script above. Unfortunately you will need to produce this using alspp and its fence feature.

It is worthwhile using the script above to divide a discrete line then using the x/y coordinates from each section for your division. This will give you a consistent split across the waveform data. If you have variable pitch/roll you will likely have to process each line seperately.

To give a fence in alspp go to filters > points on the ground. In the dialogue that displays click "selected projection (x,y,z)" then enter the min/max of your x/y coordinates for a square.

Alspp will not run on waveform data simultaneously with another alspp instance.

Seemingly at random some lines will not process with the fence options that every other line in the dataset will run under. This will result in an output of 22.6 k las files, you will need to change the fence size or in some cases create an entirely new alspp reg file to overcome this bug.