When working with Environmental Consultants / Engineers there are terrain and water resources available via Government Websites.
This blog will focus on how to process LIDAR (Light Detection and Ranging) data in Civil 3D and then generate a Digital Terrain Model (DTM) from the point cloud.
Many consultants use ESRI ArcGIS for their analysis and mapping services. Civil 3D has the capabilities to perform GIS analysis, but in order to coordinate with ESRI consultants, we may be asked to process our data and export that information to other GIS formats such as shape files or as a Digital Elevation Model (DEM).
- The first step is to acquire or receive the LIDAR data usually a point cloud with .las or .laz extensions.
- Use Autodesk Recap Pro to process the Lidar file. Recap Pro will read the Lidar data and unify the scans into a single file. The results will be a file with a .RCP extension that Civil 3D can read.
- Use the Preferences button to set a coordinate zone for the LIDAR file:
- Set the coordinate system in Recap.
- Export the point cloud:
- Save your .RCP file.
- Next, start a new C3D drawing and immediately setup your drawing in the correct coordinate space consistent with the LIDAR data coordinate system. Save your drawing.
- Import the processed point cloud. Use the Attach function in the Insert tab --> Point Cloud panel.
- Now that the Point Cloud is imported, you can verify the Geolocation is correct by using the Online Map feature in the Geolocation tab.
- If the BING Imagery displays, then you have confirmed you are in the correct Geolocated Coordinate System and can process Civil 3D objects to design and export for sharing with your team members.
- At this stage, you may generate a Digital Terrain Model (DTM) from the imported point cloud.
- Select the frame of the Point Cloud. The contextual ribbon will switch to the Point Cloud tab.
- Select Create Surface from Point Cloud and provide info via the wizard:
- There are 3 options in the Point Cloud selection: For this situation, the entire point cloud is being processed.
- Select the entire Point Cloud
Non-Ground Point Filtering provides the option of Planar average: Use to filter out trees and buildings / structure heights.
Kringing interpolation: Use this for a more sophisticated filter to exclude trees, towers, bulding heights...
Or No Filter. You would most likely select this if the LIDAR file has already been filterd to represent ground points only (Bare Earth).
- Select Create Surface and C3D will process the surface in the background. This is a very time consuming process and the amount of time will depend on the number of points in the LIDAR. You may need to let the process run overnight.
- After processing, the surface will appear in the Prospector: Under drawing objects the Description will reflect the LIDAR Grid file.
- The PointCloud can be detached or unloaded. The file will show up in the External Reference Palette.
- The surface can be handled like any other DTM.
Contour Intervals and other Analyses can be performed on the Surface. The resulting surface can be edited, simplified and exported as a LandXML or DEM file.
Important note: Due to LIDAR files having extremely large data points, a DTM created from the LIDAR will likely create an external file that will need to reside in the same directory as the surface. The external file will need to be provided to anyone who will need to use this surface.
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