Virtual Surveyor contains a complete toolbox that helps you easily survey roads from drone data. This article provides a step-by-step guide for going from drone data to a CAD road file. The section lines method is inspired by traditional road survey techniques and allows you to deliver lightweight road surface models.


Overview


Draw a Centerline

The drawn centerline is the backbone of the road and the first survey item captured in our workflow. In Virtual Surveyor, we only use the drawn centerline to create the survey lines and give us reference to the section line alignment. We hide the drawn centerline before producing the TIN because the created section lines provide us with a clean centerline once the workflow is completed.


To avoid perspective distortions, and to make centerline detection easier, use the 2D view mode. In general, you can draw the centerline—based on the road marking using the Polyline tool; a section line is added on each vertex. To keep the CAD model lightweight, use as few clicks as possible to survey the centerline. When surveying a turn in the road, you typically need more vertices to accurately capture the curve.  



Create Section Lines

  1. Select your created centerline and go to the Create group that is available in the TOOLS tab. 
  2. Set the Along and Across values for your project. 
    1. Set the Along value to 100 ft or 30 m.
    2. Set the Across value to 100 ft or 30 m.
  3. Click on the Section Lines button to create section lines at the set values. 


Once the section lines are created, notice that a Boundary is automatically created around the section and centerlines.



Model the Topography

Now that the section lines are created, we need to drape the section lines and boundary to the terrain and create vertices for the lines. 


Model the Boundary Line

The Boundary will likely drap over vegetation and other obstacles on the terrain. You want to use the Densify tool to ensure the line and vertices are only included on the terrain. We can use the Low-Pass method to do most of the work for us:

  1. Select the Boundary and go to the TOOLS tab.
  2. Go to the Densify section and set the Method and Distance.
    1. Set Method to Low-Pass.
    2. Set Distance to 10 ft or 3 m.
  3.  Now click Densify to create additional vertices on the Boundary.

We will clean the vertices later, for now move on to Section Lines and perform the process in a similar manner.


Model the Section Lines

Newly created Section Lines hover over the terrain topography when initially created. To drape your lines to the ground, we'll use the Densify tool again, except use the Regular method. 

  1. Select all Section Lines and go to the TOOLS tab. 
    1. You can select all section lines by selecting the Section Lines layer in the Project View.
    2. You can also select all lines by holding Shift and clicking the first and the last section line in the Project View.
  2. In the Densify section, set the Method to Regular and set the Distance to 10 ft or 3 m
  3. Click Densify

The next steps are for cleaning the vertices on the lines.



Clean Up Lines

Now that the lines are modeled to the topography, we need to clean both the redundant section lines and the vertices from where they should not be included on the terrain.


Redundant Section Lines

In addition to section lines placed according to the distance of the Along value, other section lines are drawn on each vertex of the centerline. Some of the created section lines are redundant and should be deleted manually. 

  1. Select the redundant section lines individually and press Delete.



Clean Up Vertices of the Boundary and Section Lines

Parts of section lines commonly appear over surface objects (trees, jerseys, rails, etc.) and require editing to fit with the road topography. The Edit Vertex feature allows you to remove or edit section line vertices that lie over those objects:

  1. Select the section line you want to edit.
  2. In the TOOLS tab, click Edit Vertex to display the vertices.
  3. Select and delete vertices where necessary. 
    1. You can select multiple vertices by holding Ctrl while selecting them. 
    2. Section—or range—selection is also possible by holding Shift and clicking the first and the last vertex of the desired group on the section line. 
  4. When all the unwanted vertices are highlighted, press Delete.


It is good practice to keep the last vertex of the line and to adapt its Z value according to the surrounding ground elevation. This maintains the section line's horizontal length. You can usually copy the last correct vertex Z value on the line and apply it to the end of line vertex (Use the Edit Z feature in the TOOLS tab).



Create the Road Surface

Once all the survey items are created, cleaned, and active (show a check in the box in the Project View), you can create a surface within the survey boundary. 

  1. Make sure you turn off the originally drawn centerline (uncheck in the Project View). 
  2. Select the Boundary and click on Triangulate Within in the TOOLStab. 
    1. The survey displays as triangles (TIN) by default. 
    2. It is possible to change the style of the surface and display the TIN as contour lines as well. 



Export the TIN

When you are satisfied with your results, you can export the results as a CAD file. 

  1. Use the Export Survey button available in the EXPORT tab.
  2. Select your preferred CAD format. 


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