Drone data usually come with noisy water surface. Indeed photogrammetric processes do not work well over such a surface and can't deliver relevant DSM on those areas. To get a surveying grade result, the noisy part of the raw DSM needs to be flattened.
Here is a quick guide to get rid of this noise in a few steps and enhance your map quality with Virtual Surveyor.
- Draw the water boundary.
- Clean the water boundary.
- Triangulate the water boundary.
- Modify the terrain.
Water body boundary
The first step is defining the water surface extend. To easily draw a line around it you can use the Extract Level tool available in the HOME tab. Click on the Extract Level button to activate the tool and then click a point on the bank at the intersection of the water level and the terrain.
If it's not easy to determine the intersection point between the water level and the terrain, you can use the Water tool available in the TOOLS tab. Draw a rough boundary around the pond, select it and click on Water. Select the water item and adjust it close to the actual water level. Click on Intersect Terrain to generate the water body boundary. Erase all those polylines except the outer boundary.
Water boundary Cleaning
Sometimes it's necessary to locally adjust the water extend limit. Due to the noisy surface or objects on that surface it's possible that the boundary doesn't follow the bank in certain place.
Use the Edit XY tool available in the TOOLS tab to adjust the vertices position. You can also delete large section of the boundary thanks to the range selection (press Shift + click first and last vertex of the range).
You may also split the boundary and create a new section manually with the Polyline tool. Make sure that all the new vertices are on the same elevation as the main boundary. After creating the new section, click on Edit Z and select all vertices (Ctrl+A) to adjust their elevation. Pay also attention to the fist and/or last point(s) of the new section, it has to be located at the exact same position as the splitting point of the water boundary. Then select both polylines and merge these.
Water body surface
Select the water extend boundary and Triangulate Within to create the plane water surface.
Select the water surface item and, in the TOOLS tab, click on Modify Terrain to remove the noise and make a flat DSM within the pond boundary.