Cull every 2nd,3rd,4th,5th at 2' elevations to create contours at 10' elevations (from GIS data)

I have a very complex set of topography lines at 2’ elevations from GIS, which comes in as a .dwg into Rhino. This is all well and good, but the area is very large (600 acres) and the topography is so complex I cannot create a terrain without crashing the computation.

NOTE: there are multiple contour lines at each elevation.

Therefor I am attempting to reduce the complexity in an attempt to build the terrain by culling curves by elevation.

This will be used for master planning purposes, so I do not need a precise terrain.

I am basing my definition on defining the curves by their Z value, simply by extracting End Points, then I have a long list of lines that I can use for culling, but I am having difficulty doing that with the Sequence component (every 10), since it does not check all the list items …

Any suggestions? It should be rather easy, but I am just not coming up with the method.

Upload file :slight_smile:

I added a Dropbox folder link with the files. The 3dm is too big!

Group curves by z coordinate and list every x branch. (78.6 KB)