Drone data often struggles to create accurate ground surface models over wooded or vegetated areas. Surveyors, engineers, and other professionals are often only interested in ground data to model the bare earth. Virtual Surveyor includes tools that help you efficiently model your bare earth surfaces.

In this use case, we are going to create a lightweight CAD model that we will export to a 3rd party CAD software for further analysis. This process allows you to avoid wasting time cleaning the terrain, so you can focus your efforts on surveying instead.


Draw a Boundary Around the Area of Interest 

First, define the area you want to survey. Use the Boundary tool to outline the area or zone you want to work within. You do not need to worry about the elevation of vertices on this boundary. 

Low-Pass Point Grid

Select the boundary and launch a Low-Pass Point Grid. Set an appropriate grid size to ensure you have a dense grid, but not so dense you saturate the vegetation with points. 

What is the optimal grid size? Start with a larger grid size and make the grid size smaller step by step until points start to appear on surface objects. Read the full details here.

Edit the Point Grid

Even though the Low-Pass algorithm is designed to place points on the ground, sometimes—in dense vegetation areas—points can land on trees. Manually remove these points by selecting them and pressing Delete on the keyboard. 

Tip: If multiple "floating" points are created on top of vegetation when the Point Grid is created, it might be simpler to delete all the points by selecting the Multi-point item in the project view and re-run the Low-Pass point grid again with a higher grid size value.

Add Breaklines

You can add breaklines to include specific elevation terrain lines on the road or bank edges. Use the Polyline tool available in the HOME tab to draw these breaklines. The Guided Breakline Tool may also be helpful if you are needing to quickly create lines over steep slopes.

Triangulate the Survey

When all the survey items are finished, disable the boundary in the project view and click Triangulate All (found in the HOME tab) to generate the surface. With the Surface selected, you can use the Styling options in the TOOLS tab to show both the TIN and the contour lines.

Review and Edit the Created Surface

There are a number of tools you can use to refine and polish your surface. With both the TIN and Contours visible, you can use the Edit surface features from the TOOLS tab to create a survey-grade deliverable without having to go back and edit or add points to the Elevation Terrain. Some tools you can use to refine the surface include (but are not limited to):

  • Edit Surface
    • Remove Vertex - quickly smooth out contours from erroneously placed vertices (see example below).
    • Add Vertex - quickly add detail to the surface that is missing information on areas of the Elevation Terrain (see example below). 
    • Remove Edge - look for and remove triangle edges that are not needed in the details of the surface.
    • Flip Edge - flip triangle edges to better fit the Elevation Terrain and give a more accurate surface representation where necessary.
  • Keep Outside - remove the house from being included in the surface information.

Using Remove Vertex to clean up erroneous points on the terrain.

Using Add Vertex to add more detail to your surface.

Export Files

When you are confident your surface is complete, you can export the lightweight CAD model to .dxf for further use in a 3rd party CAD software.

Tips and Tricks

  • If your project contains only a few isolated trees, it is not necessary to use the Low-pass Point Grid. You can easily exclude these surface objects from your surface model by deleting the survey points off of them.
  • To easily locate incorrect points generated by the Low-pass tool, triangulate all the points and enable surface contours with a small interval. Points created on top of the vegetation are represented by clustered concentric contour lines. You will more easily see those "pyramid" contours by activating the Transparent Terrain Lens.

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