Photogrammetry Mesh to Rhino Surface Topography

Grasshopper
1

I am trying to create a rhino surface (site topography) from a photogrammetry mesh (from drone reality capture / use of the Heron plugin). Conceptually, I am sticking a bunch of vertical lines into the photogrammetry and using all of those intersections (points) to create a nurbs curve and eventually loft them into a rhino surface. I realize the Heron plugin can provide a topographic surface but it is not super accurate in my experience, especially if you crank up the resolution on the Heron Photogrammetry brought in. Please let me know if I am approaching this solution from the wrong angle. Otherwise, I am sturggling with two major things in my process:

  1. The sample photogrammetry in the file below is broken up into open meshes. I am trying to use the path mapper to group my points in a straight line for nurbs curve generation. (See top image in PDF below)

  2. How to “smooth” out the surface from buildings, tress, cars, etc. Would I take average sampling of surrounding point z values? Or should I try to overwrite the z values that are extremities?

Any thoughts on this would be greatly appreciated!

MeshtoSurface.pdf (1.5 MB)

MeshtoSurface.gh (37.8 KB)

MeshtoSurface.3dm (1.9 MB)

2

The biggest issue is the low resolution of the mesh.

Anything you do with nurbs will decrease the accuracy due to interpolation, unless you simply convert each triangle to a nurbs surface. Creating a nurbs surface from each triangle is typically not the approach to create a nurbs surface but in this case it may be the best option. You can sample more points on the mesh, but generating curves and a surface based on sample points will still result in interpolation.

If you can get a higher resolution mesh from the photogrammetry you could end up with a result with better accuracy, although it would still be interpolated.

3

No difference in accuracy between using the mesh faces directly for interpolation or using the mesh faces converted to individual NURBS surfaces for interpolation.

4

Right, the difference in accuracy (interpolation) is when curves are used to generate the surface. Since the mesh is very low resolution, interpolation may be significant.