Virtual surveyor contains a complete toolbox that helps you to easily survey roads from drone data. This article provides a step by step guide to go 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.
- Draw a center line.
- Create section lines.
- Model the topography.
- Clean up.
- Create a boundary.
- Create the road surface.
The center line
The center line is the backbone of the road. It's the first survey item to be captured. The center line is also usually part of the required survey items and it will determine the alignment of the section lines.
To avoid perspective distortions and to make center line detection easier let's use the 2D view mode. In general, you can draw the center line based on the road marking using the Polyline tool. A section line will be added on each vertex, so to keep the CAD model lightweight, use as few clicks as possible to survey the center line. Obviously, in turns, you need more vertices to properly capture the curves.
The section lines
When the center line is ready, go to the Create group available in the TOOLS tab. Once both Along and Across values have been properly set for your project, you can click on Section Lines button to automatically create sections lines at your set values.
Section lines do not conform to the terrain topography when initially created. To drape your lines to the ground use the Densify tool available in the Transform group of the TOOLS Tab.
Select all section lines through the project view. Set the density method to break points and make sure to set the elasticity low enough to capture topography details. Now, click on the Densify button.
In addition to section lines placed according to the distance of the Along value, other section lines have been drawn on each vertex of the center line. Some section lines are redundant and should be deleted manually. Select the redundant section lines and press Delete.
Parts of section lines will also commonly appear over surface objects (trees, jerseys, rails...) and require some editing to fit with the road topography. The Edit feature helps you to remove or edit section line vertices that lie over those objects.
- Select the section line that requires editing.
- In the TOOL tab click on Edit Vertex button to display the vertices.
- Select and delete the wrong vertices. You can select multiple vertices by holding Ctrl. Section or range selection is also possible by holding Shift and clicking the first and the last vertex of the desired group. When all the unwanted vertices are highlighted, press Delete.
- It is a good practice to keep the last vertex of the line and to adapt its Z value according to surrounding ground elevation. This will maintain the section lines 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).
The survey boundary
To limit the extent of the road survey, a boundary is used. You can select all the section lines through the project view and use the Concave Hull feature to automatically create this boundary. Manually adjust the hull where required with the Edit tools.
The road surface
When all survey items are created and active(checked), you can create a surface within the survey boundary. Select the boundary and click on Triangulate Within in the TOOLS tab. The survey displays as triangles (TIN) by default. It is possible to change the style of the surface and to display the TIN as contour lines.
When you are satisfied with your results, you can export it as a CAD file. Use Export Survey button available in the EXPORT tab and select your preferred CAD format.