[GIS] Exporting ground returns (.las) from classified point cloud

classificationdemexportlaslidar

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.

Best Answer

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.

Related Solutions

[GIS] Determining bare earth DEM from unclassified LAS file

Generating LiDAR DEMs from unclassified point clouds with:

MCC-LIDAR - Multiscale Curvature Classification (MCC) algorithm.
_{(supports LAS versions 1.1 to 1.3)}

MCC-LIDAR is a command-line tool for processing discrete-return LIDAR data in forested environments (Evans & Hudak, 2007).

Workflow:

a) unclassified point cloud.
b) ground returns classified.
c) bare-earth DEM (raster).

enter image description here

Let's create a hypothetical situation to further provide an example with code.

MCC-LIDAR is installed in:

C:\MCC

The unclassified LiDAR point cloud (.las file) is in:

C:\lidar\project\unclassified.las

The output which are going to be the bare-earth DEM is in:

C:\lidar\project\dem.asc

The example below classifies ground returns with the MCC algorithm and create a bare-earth DEM with 1 meter resolution.

#MCC syntax: 
#command
#-s (spacing for scale domain)
#-t (curvature threshold)
#input_file (unclassified point cloud) 
#output_file (classified point cloud - ground -> class 2 and not ground -> class 1)
#-c (cell size of ground surface)
#output_DEM (raster surface interpolated from ground points)

C:\MCC\bin\mcc-lidar.exe -s 0.5 -t 0.07 C:\lidar\project\unclassified.las C:\lidar\project\classified.las -c 1 C:\lidar\project\dem.asc

To understand better how the scale (s) and the curvature threshold (t) parameters work, read: How to Run MCC-LiDAR and; Evans and Hudak (2007).

The parameters need to be calibrated to avoid commission/labeling errors (when a point is classified as belonging to the ground but actually it belongs to vegetation or buildings). For example:

enter image description here

The MCC-LIDAR uses Thin Plate Spline (TPS) interpolation method to classify ground points and generate the bare-earth DEM.

_References:

_{Evans, Jeffrey S.; Hudak, Andrew T. 2007. A multiscale curvature algorithm for classifying discrete return LiDAR in forested environments. IEEE Transactions on Geoscience and Remote Sensing. 45(4): 1029-1038.}

_{For more options about ground point classification algorithms, see Meng et al. (2010):}

_{Meng, X.; Currit, N.; Zhao, K. (2010). Ground Filtering Algorithms for Airborne LiDAR Data: A Review of Critical Issues. Remote Sensing, 2(3), 833–860. doi:10.3390/rs2030833}

[GIS] Open-source reader of Leica C10 terrestrial LiDAR proprietary file format

You might check whether or not the C10 .bin file is actually a TerraSolid file. PDAL provides a reader for TerraSolid .bin plus numerous other point cloud formats.

Best Answer

Related Solutions

[GIS] Determining bare earth DEM from unclassified LAS file

[GIS] Open-source reader of Leica C10 terrestrial LiDAR proprietary file format

Related Question