LIDAR data has become the go to data capture method for terrain modelling, it is also used for many other applications including forestry planning and management, agriculture, micro-topographic studies, environmental assessments and air pollution modelling to name but a few.
Lidar point cloud data is often supplied in either .las or .laz (a compressed version of .las) files. These files have multiple fields of data in them including, Z (Elevation), R, G, B, Intensity, classification, Scan Angle and more.
The original contractor who has been tasked with data collection will have collected this to a specific specification similar to above format. The Z column providing the elevation values will contain all values in the point cloud. When using a standard interpolation method such as Triangulation and the Z column the end result will be a digital surface model. DSM’s contain all of the features that are on or above the ground, such as vegetation, buildings etc. This is not always required, a more widely used product is a Digital Terrain Model. A DTM only represents the ground surface itself, all features such as trees, building, telegraph/lighting poles etc. will have been removed.
In MapInfo Pro Advanced (v17.0 onward), the Create Raster and Create Raster Multi-File operation’s have the ability to quickly and easily filter these other fields from the dataset as part of the create raster process.
In MapInfo Pro Advanced, after selecting Create Raster Multi-file from the main ribbon, use the Add Files option to select the .laz files required to gridded in a batch process.
Select the Column Z, set the projection and click OK.
In the Create Raster dialogue, under the Group drop down, select Classification from the drop down menu. A new task window will appear. It will list all of the available classifications.
In this example, just Ground class has been selected. This represents the elevation value for the terrain. Use the Remove button to remove the unwanted classifications.
See AttachmentSee Attachment
Choose the relevant file name and Process the .laz files.
The difference in results can be seen in the images below. The first image is a DSM, all classes in the .laz file have been interpolated.
This second image is a DTM of the same area. Only the chosen group values for Ground have been gridded. This grid is better for both visualisation of the terrain and accurate grid calculations and terrain analysis.
.Las downloaded Data © National Geographic Information Center (CNIG) NIF