Lidar (Light Detection and Ranging) uses optical remote sensing technology that can measure the distance of a target by illuminating the target using pulses from a laser.
Aerial 3D Lidar data is available to NHDOT staff. The Lidar files (.LAS) are stored in N:\Aerials\2010\LIDAR\.
To see which files are available in your project area, attach N:\cadd\cadd\GIS_To_MicrostationV8\lidar-index.dgn as a reference file. This can be done in MX v8i or in MicroStation. Be sure to select the Coincident-World orientation when attaching the file.
If files are available for the desired area, a rectangle with the file name will be displayed. The text contains the name of the file. For example: 0900002250.las refers to the file N:\Aerials\2010\LIDAR\0900002250.LAS, just simply write down the file names displayed on this reference file.
1. In MX v8i using the Data Acquisition Task Menu, select the Data Acquisition tool to open the Data Acquisition panel.
2. On the Data Acquisition panel, right-click on the Surfaces branch. Then select Create Surface > Import External Surface... > Import Lidar LAS from the submenu.
3. From the Open file panel, navigate to N:\Aerials\2010 LIDAR\ and open the desired file. The Lidar LAS panel shown below allows control of data filtering prior to loading into Data Acquisition.
4. There are multiple data classifications offered in a Lidar file. In the Selected Features section of the Lidar LAS dialog, choose the classifications you wish to import (such as Ground). Next, select the Filter settings to be used for this import.
- For one or two sections use the Tile Filter with Z Tolerance set to 0.2.
- If you are intending to import multiple files use the Tin Filter set to Fine.
The Filter button will give an estimate of the percent Reduction, however it is not a necessary step for this process. Click the Accept button to import the Lidar file. Note that it might take some time to process and if you are importing several files it may crash your session.
From the Data Acquisition panel, expand the Surfaces branch to see the imported Lidar files. To display a file, check the box next to file entry. Consider that his takes time and memory. Repeat steps 3 and 4 for each Lidar file desired.
5. After importing each surface, they should be clipped down to the project's extent. Draw a Closed Element around the project and select it with the Element Selection tool. Right-click on the imported surface and select Clip by Polygon... > External. Clip all imported surfaces.
6. Next the surfaces need to be combined. Right-click Surfaces > Create Surfaces > Empty Surface to create an empty (receiving) surface for combining the individual surfaces. Right-Click this new surface (Surface X) and use Append From...> to combine each surface into it.
8. The receiving surface can be renamed by using the Data Acquisitions Details box. Highlight the name and key in a new one (such as TRIANGLESLIDAR). The name will update in the Data Acquisition panel. To create MX triangle strings, the combined surface must be exported to the MX Model file. Right-click on the renamed surface and select Export to... > MX modelfile, then select the project's model file and click Save.
Close the Data Acquisition tools and continue with your design. Your Lidar surface is now an MX triangle model. Set the Model Defaults to MFW Triangulation.pts & MFW Triangulation.fns. Consider Trimming these triangles to eliminate triangles from spanning void regions. From the Analysis menu, select Triangle > Trim Triangulation... Refer to MX Triangulation for details on Triangle Trimming.
For additional information on the Data Acquisition tool open the help file C:\Program Files\Bentley\MX V8i\Documentation\Civilmaster.chm
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