Exporting ground returns (.las) from classified point cloud?

Question

I have lidar data that is classified as several categories (water, ground etc.).

I need to open this lidar data in some software (it will be great if it would be a open source software) and delete a couple of them to leave only ground category.

Afterwards I have to export this data as *.las format again.

Answer 1

You can use the open-source liblas tools for this. The command is,

las2las --keep-classes 2 -i input.las -o output.las

To do many files, use a loop.

for f in *.las;
do
    las2las --keep-classes 2 -i $f -o $(basename $f .las)_gnd.las
done

These commands are, of course, for linux, unix or OSX. liblas is also available for Windows through OSGeo4W.

Answer 2

I used SAGA for the evaluation of my LIDAR data and some easy processing.

Go to tool libraries > Import/export > LAS. When you import the LAS data using Import LAS Files you can select the import of existing classifications (this should be your categories). Unfortunately, my LIDAR data don't have categories so I can't try it myself.

You can select points using tool libraries >Shapes > Point Clouds > Point Cloud Reclassifier / Subset Extractor.

If you want to save this selection as LAS data, you need to export it as LAS file using Export LAS Files (right click > save as saves the file automatically in the SAGA file format .spc).

Here, you'll find a tutorial about processing LIDAR data with SAGA.

Answer 3

With Fusion, the command line to be used is ClipData together with the switch /class.

It can clip las data according to the return classification and within specific area of interest.

The generic command line would look like this:

ClipData /class:2 InputSpecifier SampleFile [MinX MinY MaxX MaxY]

/class:2 is because the required category is ground, which the standard classification is equal 2.

In this post, I provided a detailed example about how to use the command line ClipData.

Answer 4

This worked for me:

1. Create a project folder somewhere. Mine is C:\GossanHill.

2. Put your .las files in there.

Get the LASTools

The programs we need don’t really need to be installed, just saved at a convenient location.

3. Get LASTools from rapidlasso.

4. Open the Lastools.zip file. Navigate to the bin folder. Copy these files to your project folder: las2las.exe, las2txt.exe, lasinfo.exe and laszip.exe. These programs are all free, open source, LGPL licensed software.

Running the LASTools

5. Open the Windows command prompt:Win + X then select Command prompt

6. Navigate to the project folder: CD C:\GossanHill.

What I did here was open the directory via Total Commander and ran cmd from there. Then you are already in the necessary directory.

7. Type a command, such as lasinfo Merged.las

I needed class 2 points and I ran las2las.exe -i in *.las -keep_class 2, but there are a lot of variations in the function.

las2las -i *.las -utm 13N
las2las -i *.laz -first_only -olaz
las2las -i *.las -drop_return 4 5 -olaz
las2las -latlong -target_utm 12T -i in.las -o out.las
las2las -i in.laz -target_epsg 2972 -o out.laz
las2las -set_point_type 0 -lof file_list.txt -merged -o out.las
las2las -remove_vlr 2 -scale_rgb_up -i in.las -o out.las
las2las -i in.las -keep_xy 630000 4834500 630500 4835000 -keep_z 10 100 -o out.las
las2las -i in.txt -iparse xyzit -keep_circle 630200 4834750 100 -oparse xyzit -o out.txt
las2las -i in.las -remove_padding -keep_scan_angle -15 15 -o out.las
las2las -i in.las -rescale 0.01 0.01 0.01 -reoffset 0 300000 0 -o out.las
las2las -i in.las -set_version 1.2 -keep_gpstime 46.5 47.5 -o out.las
las2las -i in.las -drop_intensity_below 10 -olaz -stdout > out.laz
las2las -i in.las -last_only -drop_gpstime_below 46.75 -otxt -oparse xyzt -stdout > out.txt
las2las -i in.las -remove_all_vlrs -keep_class 2 3 4 -olas -stdout > out.las
las2las -h

8. When you’re done, type exit

The output is: your_las_1.las as ground points.

Answer 5

lasground.exe in the LASTools mentioned above. This can be run from command line prompt very cleanly.