Build difference between measured topography data and volume model

Hi together,

I am using Rhino for quite a while, however so far just for simple volume modeling and .stl export for micromachinig.

Now I have a new task where I got a little bit stuck and need some help. I want to model the differene volume between measured 3D topography data (stl or polygonmesh) and an (ideal) volume model which can be stl-Data or a volume model in Rhino. For testing I designed a cone and a little bit deformed cone like surface in rhino, exported both to .stl and reimported the data. My approach was to rebuild volume models out of the .stl data (conversion to NURBS) and perform a boolean difference.
As I found out in this forum this makes not so much sense as rhino models volumes as objects with boundaries and not like filled volumes with voxels. All my tests lead to a not working boolean difference.

So I am now asking myself if Rhino is the right tool for this operation and if yes how I can move on? I guess this is not such a simple task, this is why I need some help to find the right approach.

Thanks for your help.


It’s hard to tell what you tested and why it failed. You can use the mesh version of boolean difference and when you get a closed mesh as the result thereof, you can get its volume with the Volume command. The problem might be with cleaning up bad input meshes - that’s definitely not Rhino’s strongest side.

Hi wim,

thanx for your fast response. I found a solution for my problem, at least for the idealized cone.
As I need the difference volume between two not overlapping meshes I simply positioned both meshes so that they are congruent in the xy-plane. Then I created a 2D plane layer mesh that cuts both cones at z=0.
After converting all meshes to NURBS I used the trimming tool to create a surface formation in the shape of the targeted difference volume. After combining the surfaces to a volume object it was simple to export it to .stl and use it for further processing.

However you are right that this will not be as easy if the mesured meshes will have holes and need to be repaired first.