Light Detection and Ranging (LiDAR) is a spatial data acquisition method that
used laser light and specialized GPS receiver. LiDAR surveying activity will
produce millions of point which is called point cloud that consist of X,Y and
Z information. Therefore using LiDAR for mapping or 3D objects reconstruction
will generate a more detail output and also cost-effective compared to
traditional surveying method.
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
Before installing the LAStools plugin for QGIS, firstly we have to download
the software from
rapidlasso. The software will be downloaded in a zip format. Extract it and then copy
to a drive. For Windows operating system, the default location is in drive C.
If you place it in another drive, then you have to set the path in QGIS. I
will show you how to do it just in a minute.
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.
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Figure 1. LAStools Plugin Installation
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To change the LAStools plugin directory path, from
Settings menu select
Options... The option window will show up as in figure 2. Go to
Processing menu on the left column, then click
Providers. You
will see all the processing tools that already installed. Here is the location
where we modify the path of the installed tools, including the LAStools. Click
the LAStools, and you will see the folder path. Just change it with your
LAStools folder path.
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Figure 2. LAStools Plugin Path
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Inspecting LiDAR Data
Now, 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.
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Figure 3. Lasinfo tool
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Open the lasinfo tool, the window will appear as in figure 4. In the
input LAS/LAZ file parameter, input the LiDAR dataset in LAS or LAZ
format. The result of LiDAR file inspection can be seen as in figure 5. From
the result can be seen some information regarding the inspected data like
creation date, number of points, coordinate system, minimum and maximuman
coordinate, classification points and so on.
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Figure 4. Lasinfo tool processing
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Figure 5. Lasinfo tool result
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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.
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Figure 6. Lasview tool
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Figure 7. Lasview window
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Splitting LiDAR Data
In 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.
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Figure 8. DEM from LiDAR with black stripes
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To split a LiDAR data can be used the
lassplit tool that can be found
in LAStools
file-processing points. The lassplit tool window can be
seen in figure 9. Like in previous tool, input a LiDAR data to be splitted.
Put
-split 1000000 in
additional command line parameter(s), this
command will split each output file with one million points. 1000000 is a
variable, so it can be any positive number. The
Output LAS/LAZ file is
the output location path. I suggest to make a new folder to store the result,
so it won't mixed up with other files. The output file(s) has
laz extension. It is a compression format of las LiDAR data. After
running the split tool, some output files in laz extension will be
generated.
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Figure 9. Lassplit window
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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.
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Figure 10. las2demPro tool window
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Figure 11. Lasinfo tool result
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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.
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Figure 12. DEM data before merging
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Figure 13. GDAL Merge Tool
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Figure 14 shows the GDAL Merge tool. In the
Input layers parameter
select all layers or files to be merged. In the Merged parameter set the
output path to store the output file. The result of merged DEM tiles can be
seen as in figure 15.
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Figure 14. GDAL Merge Tool
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Figure 15. Merged DEM
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Hillshading
Before 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
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Figure 16. Layer Properties Window
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Select
Symbology on the left menu then select
Hillshade option
in the
Render type parameter. Finally hit
OK button and the
hillshading result of DEM can be seen as in figure 17. Comparing with figure
8, now the diagonal black stripes are gone. Nice! Furthermore if you want to
visualize the DEM in 3D view just check out another tutorial
3D DEM Visualization in QGIS.
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Figure 17. DEM with hillshading visualization
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That's all the tutorial how to process LiDAR data using LAStools in QGIS 3. In
this tutorial we had learnt how to inspect LiDAR data, viewing LiDAR data,
creating DEM from LiDAR data and visualize it in hillshading mode to get a
better depth visualization. Check out this
tutorial to make a beautiful hillshade map. LAStools is a powerful tool that can do other processing tasks. If you want
explore more about LAStools just check out
rapidllasso GmbH
web page.
LiDAR
QGIS
Tutorial
