There are many software or tools available to process LiDAR data such as: Global Mapper LIDAR module, ArcGIS LIDAR, Merric MARS, TerraSolid, ENVI-LIDAR and many more. In this tutorial I will discuss how to process LiDAR data using LAStools in QGIS 3.
The following topics will be discussed in this tutorial:
- How to install LAStools in QGIS 3
- How to inspect LiDAR data
- Viewing LiDAR data
- How to create Digital Elevation Model (DEM) from LiDAR data
Installing LAStools Plugin
After downloading and extracting the LAStools, next we will install the plugin. As usual, to do a plugin installation in QGIS, open Manage and Install Plugins.. from Plugins menu. The plugins installation window will appear as in figure 1. In the search box type lastools, immediately the QGIS LAStools plugin will show up. Check it, then push Install Plugin button.
|Figure 1. LAStools Plugin Installation|
|Figure 2. LAStools Plugin Path|
Inspecting LiDAR DataNow, let's see the LAStools in action. For this QGIS LAStools tutorial I used a classified LIDAR data from North Dakota that can be downloaded at North Dakota LiDAR Dissemination Map Service. The Lidar dataset that was used in this tutorial can be downloaded here.
For the first action, we will inspect the LiDAR data using Lasinfo tool. The tool can be found in LAStools file-checking quallity in the Processing Toolbox as in figure 3.
|Figure 3. Lasinfo tool|
|Figure 4. Lasinfo tool processing|
|Figure 5. Lasinfo tool result|
Viewing LiDAR Data
Next, let's see how is the data looks like. To view a LiDAR data, the lasview tool is used. The tool can be found also in the LAStools file-checking quallity (See figure 3). Figure 6 shows the Lasview window. In the input LAS/LAZ file parameter, input a LiDAR data to be viewed. Push the Run button to start the process. When finished, the preview window of the input LiDAR data will be opened as in figure 7. Play with it by rotating, rendering by specific object, changing the color, etc.
|Figure 6. Lasview tool|
|Figure 7. Lasview window|
Splitting LiDAR DataIn the next part of this tutorial, we will create Digital Elevation Model (DEM). We begin this process by splitting the data. This step is required prior processing the data into DEM to prevent diagonal black stripe as shown in figure 8 in the result. How could the black stripe appears? Where is it come from? Actually the LAStools is not fully free tools. When the number of points exceeded 1.5 million, the black stripe will be inserted to the result. One way to overcome it is by splitting the data. Otherwise consider to purchase the license, especially when you're working with large area.
|Figure 8. DEM from LiDAR with black stripes|
|Figure 9. Lassplit window|
Creating Digital Elevation Model (DEM)To create DEM from LiDAR data using LAStools can be done using las2dem or las2demPro. las2dem is a single file processing tool. On the other hand las2demPro is multiple files processing within a folder. Because we have some files form previous split process, then las2demPro is a right choice. The las2demPro tool can be found in LAStools folder-raster derivatives.
Figure 10 shows the window of las2demPro. In the input directory parameter specify the folder where contains all files to be processed. Depends on file extension whether las or laz, set the parameter of input wilcard(s). The filter parameter is very important in this step, because in creating DEM, we have to exclude all points except ground points. For this, we must select keep_class 2 option in the filter parameter. The default classification number for ground point in LiDAR data is 2. To check the number of point classification can be done also using lasinfo tool. Figure 11 is the result of lasinfo that shows the number of points and it's classification class.
|Figure 10. las2demPro tool window|
|Figure 11. Lasinfo tool result|
Merging DEM Data
After running the las2demPro tool, the DEM data in tif format will be created as shown in figure 12. At the boundary of each DEM tile can be seen a straight separation line of each tile due to tone color difference. Actually nothing wrong with it, just a visual effect. If the area if not large enough and could be rendered smoothly, merging all the tiles is a good approach.
To merge all the tiles can be used GDAL Merge tool. To find the tool type merge in the Processing Toolbox searching option, and look at the tool below GDAL tool as shown in figure 13.
|Figure 12. DEM data before merging|
|Figure 13. GDAL Merge Tool|
|Figure 14. GDAL Merge Tool|
|Figure 15. Merged DEM|
HillshadingBefore ending this tutorial, let's visualize the DEM with hillshading to get a better depth visualization. Add the merged DEM file to QGIS map canvas. Then right click the layer and select Properties. The layer properties window will appear as in figure 16
|Figure 16. Layer Properties Window|
|Figure 17. DEM with hillshading visualization|