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Create Terrain from LiDAR Data

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 from multiple sources. NH GRANIT provides one source of this data and it can be found at http://lidar.unh.edu/map/. This site displays a map of our state with shaded areas indicating where LiDAR coverage is available. Zoom in to the region of interest to see what may be available. Any area that shows as covered may have multiple files to choose from.

LiDAR coverage areas

LiDAR Coverage Areas

For files that are available for the desired area, the best results are achieved by choosing the Classified LAS version for the selected year (see image to the right). These "classified" files have been post-processed to indicate whether points are buildings, water, vegetation, etc. Views can be modified based on these feature classifications.

There are Filter options above the state map to select the specific files of interest. Use the Custom Selection Button to specify an area of interest. You'll be prompted to click and drag a rectangle to define this area. Once a filter has been selected, a Green Button will appear to the right of the state map (shown below) that indicates the number of files meeting the selection criteria.

Selected LiDAR files

Selectecd LiDAR Files

If the file count seems accurate, then click the Green Button to get a prompt for an email address to receive the requested data. An email will be sent in a few minutes to this address with a link to download the LiDAR data files. In Windows 10 this file is placed in the Download Folder.  The files will likely arrive compressed (zipped) and appended with a ".zip64" file extension. This file extension should be changed to a ".zip" extension before attempting to Extract from it. Then Extract the files from this zipped file.

Create Terrain from LiDAR LAS Files

From the MX menu, select Open Plan Display to open the Terrain-lidar.dgn. If this drawing does not exist, then create a New Plan Display called Terrain-lidar.dgn using on the appropriate OpenRoads seed file Once in, open the Default-3D model because this process doesn't work in 2 dimensions.

From the CADD menu, select File > Point Clouds to get the Point Clouds manager shown below:

Point Cloud Manager

Point Cloud Manager

From the Point Cloud manager, select File > Attach... On the Open file panel, change File of Type to LAS (*.las) and navigate to the directory where the extracted LiDAR file(s) resides. Select the LiDAR file(s) and click Open.

A properties panel with the title of Convert LAS will appear with some information about the first file to be processed. This panel will be used to convert the LAS file to a POD format that is needed for OpenRoads. But first, in the Option Section, note that the Geometry Unit setting may display the most recently used setting, not necessarily the correct one for the files being imported. If using the Connecticut River Watershed (2015) files, change this value to US Survey Feet. Other files seem to work better when this value is set to Meters.

Click the OK button to convert this LAS file. Save the resulting POD file to the Project's MX Directory. A Convert LAS panel will return if there are more LAS files available to convert. Repeat until each LAS file is converted.

Issue the Fit View command to adjust the view to include all of the attached files. If necessary, select the Point Cloud(s) in the Point Clouds manager and turn ON the display for the current view. The Presentation Style needs to be changed in View Attributes. From there, change the Point Cloud Presentation Style to Classification & Intensity.

Next, the Presentation Settings need to be modified from the Point Clouds manager. Select Settings > Presentation to get the Point Cloud Presentation panel. Under the Classification Settings, uncheck all the boxes except for the Ground, Low Point and Water styles. It should look something like this:

Point Cloud Presentation Options

Point Cloud Presention Options

point cloud export

Export Point Cloud

From the Point Clouds manager, select all the files and use File > Export to get an Export Point Cloud panel. From here we can create a new combined point cloud.

From the Export Point Cloud panel, adjust the Classification Filter to only export just the Ground and Water. Do this from the pull-down, place checks for just the items to export. When complete, the Classification Filter option will display 2 Classes. Also, set the Channels> Classification to Include (both are shown to the right).

Hit the OK button and specify a new file name for the new POD file. This will create a single POD file with just the ground data removing any data that has been classified as tops of buildings and treetops.

In the Points Clouds manager, Detach the original POD file(s) and then Attach the new file just created. Turn ON its display if it is not already visible.

If the entire area covered by the POD file is not needed, then Place (a) Fence just around the area to be converted to a Terrain.

Select the Create from Point Cloud tool from the Terrain Model task menu. Select the options as shown below:

Import Terrain from Point Cloud

Import Terrain from Point Cloud

Click the Import button to generate the Terrain. The dialog at the bottom of this panel will report when the import is done. Since this panel does not automatically close after the import is completed, close the Create Terrain From Point Cloud panel when done.

From the Point Clouds manager, either select the POD name(s) then shut off their display in all views, or Detach the file(s) entirely. From the CADD menu, select Save Settings and then Save the new drawing file.

There should now be a Terrain model in the Default-3D model. It's Feature Definition can be changed to Exist_Boundary if desired. The Feature Name can be updated using Element Information.

Drape an Aerial Photo over the triangles to enhance the view.


New Hampshire Department of Transportation
PO Box 483  |  7 Hazen Drive  |  
Concord, NH  |  03302-0483
Tel: 603.271.3734  |  Fax: 603.271.3914