Virtual surveyor contains a complete toolbox that helps you to easily survey roads on the basis of drone data. This article describes 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 to deliver lightweight road surface model.
- Draw a center line.
- Create section lines.
- Model the topography.
- Clean up.
- Draw a boundary.
- Create the road surface.
The center line
The center line is like the backbone of the road. It's the first survey item to capture. The center line is 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. If both Along and Across values have been properly set, you can click on Section Lines button to place the section lines.
Section lines don't follow the terrain topography yet at this point. To project those lines on 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. Click on the Densify button.
In addition to section lines placed according to the Along value, other section lines have been drawn on each vertex of the center line. Some section lines are redundant and should be erased manually. Select the redundant section lines and press Delete.
Some section lines appear over surface objects (trees, jerseys, rails...) and need some cleaning to make them fit with the road topography. The Edit feature helps you to remove or adapt section line vertices that lie over those objects.
- Select the section line that would need a clean up.
- In the TOOL tab click on any button from the Edit group (On Terrain, XY or Z) to make the vertices visible.
- Select and delete the wrong vertices. You can do multiple vertices selection by holding Ctrl and clicking all the unwanted vertices. Range selection is also possible by holding Shift and clicking the first and the last vertex of the 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. It maintains the section line 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 extend of the road survey, we use a boundary. You can select all section lines through the project view and use the Concave Hull feature to draw this boundary. Manually adjust the hull where required with the Edit tools.
The road surface
When all survey items are generated and 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 by default. It is possible to change the style of the surface and to display the triangles with contour lines or to show the contours .
When you are satisfied with your road survey, you can export it as a CAD file. Use Export Survey button available in the EXPORT tab and select you favorite CAD format.