LiDAR technology has become a prominent technique for acquiring highly dense and accurate information for physical features of the earth. As LiDAR technology is a nonselective acquisition method, the acquired data consists of a point cloud that includes bare-ground and non-ground objects such as trees, roads and buildings. Filtering methods which involves removing of non-ground points, have been the need of various analysts for surface creation or feature extraction. Various applications exist to perform one function or the other such as some support surface creation, a few allow filtering of data whilst others allow analysis of created surface or create derivatives. These daunting task of working with Lidar file (LAS) is made easier with MapInfo Professional. Processing of single or multiple las file, generating surface based on various lidar parameters such as elevation, intensity, scan angle, classification etc., extracting required classification from classified raster, providing custom projection information is just a button click away with Raster tool of MapInfo Professional.
Various lidar dataset are available in public domain for US. A few important ones are
Once the lidar dataset is acquired from any of the above weblinks or others, a few steps need to be performed in MapInfo Professional to slice and dice bare ground and non-ground objects to create raster surface. So here are the steps to create bare-ground elevation surface using multiple lidar files (*.las) using MapInfo Professional.
- On the Raster tab, in the Interpolate group, click Create Raster Multifile to display the various interpolation methods available and click nearest neighbor
- Select file format type LIDAR ASPERS LAS Files (*.las) and click OK
- Select folder dialog box displays. Navigate to the folder where lidar (*.las) data is available and select folder.
- Define Input Parameter on the basis of which raster can be created such as Z, Intensity, Classification, Scan Angle etc. Since elevation raster needs to be created, Z is selected as input as its contains height information.
- Define Projection of these lidar files. Mostly projection information is available in *.xml provided along with lidar. But if projection information is known prior, enter it under Projection Category and SubCategory both information need to be filled to project lidar correctly. Click OK.
- The Create Raster dialog box displays. To filter data based on specific parameter such as scan angle, classification etc., Click Group By option for filtering data. Here Classification is used as filtering parameter and Ground class is selected (discarding Unclassified and Water classes) to create bare ground raster.
- Interpolation can be changed using Select Method drop-down list. The method chosen in step one above will already be selected so you only need to do this if you wish to change the selected interpolation method.
- In the Raster Geometry section, specify the cell size and raster bounds for the output raster. Suggest option is available as well which help calculate default cell size but explicit Cell size can be specified as well based on required raster resolution.
- Select define Output Geometry check-box to clip the output data points according to specified region (bounds) and reject all points that lie outside of the specified region (optional).
- In the Output File box enter the name for output file. Click to browse to the location in computer to save the output file and select the required output file format. Display Output File - Select the check-box, if you want to open the output file in the Map window on completion of the operation.
- Click Process to start processing your lidar data. Once process is complete "Elevation Raster with Bare Ground" is generated!!
Raster surface with bare earth model has applications in various verticals. Multiple product derivatives can be generated such as elevation profile which is extremely useful for flood underwriters and risk analysts, slope and aspect information to understand landslide risks, and many more. Besides sculpting bare ground elevation, canopy height models, understanding forest structure and shape of the trees, light intensity and more can be derived from single lidar file. So, what are you waiting for? Grab a copy of MapInfo Professional and start exploring lidar!!
Dr Neena Priyanka
Pitney Bowes Software