To create a DTM from a point cloud, it is typical to classify the data to ground and non-ground layers of points. For our program, a ground classified LAS or LAZ is a requirement. Once the points are classified, a user could move on to manual digitizing if they had to, or they could send it to our cloud-based software. They also need to create a closed polygon that defines the area of interest (AOI) within the point cloud that they wish to have processed. This can be either a shape file (SHP) or a drawing interchange file (DXF).
Once the classified LAZ and the AOI are ready, they are uploaded through our site to secure storage at AWS. Our system begins by creating a preview of the point cloud showing the AOI overlayed on it. This is a reality check for the user to make sure they have uploaded the correct data and that they are in matching locations. Once they see the preview, they can either cancel or run the project.
From there, the project is displayed in their active projects table and will show a status of “in progress” until it is complete. Most projects are completed within an hour or two, though we’ve had a few that took just over a day. When the project is completed, you can download a ZIP file that contains three complete sets of breaklines created at varying densities (Low, Med, High). The low-density data is usually much smaller but is still extremely accurate. In the high-density version, we’re looking for even the smallest grade breaks, which results in more data and detail.
The breakline data comes as a SHP file that can be imported into the desired DTM software, such as Civil3D or Microstation. We also collect a grid of points in areas where there are no grade breaks. This provides definition to the terrain where the relief is flat, has a regular slope, or is rounded, but doesn’t have any sharp edges. This grid of points is also provided in a SHP file. Then the user can create the surface by adding the breaklines and points into the DTM object.