mesh intersection problem

Hi all,

I'm facing the problem that the Intersection.MeshMeshFast method doesn't work properly. Neither does the MeshMeshAccurate and MeshPlane method. I would like to intersect a mesh terrain including building information in such a way that i receive lots of vertical cuts of the terrain which i could cut out by laser.

The pieces could then be slided on a rod and pulled together, forming an accurate physical model representing terrain and building information.

In the beginning I have the terrain and buildings on a layer each, in mesh format.

With the boolean difference method I merged the buildings to the terrain in such a way that...

... the buildings and the terrain form ONE open mesh. This is necessary because...

...the intersection lines, which result from many vertical intersectin planes/meshes have to be a ClOSED polyline each.

That's where the problem is, as you can see from the image the lines are not continuous. I wonder how I can fix this bug?

Thx for help and hints)

Best

Hjalmar

Replies to This Discussion

Permalink Reply by Florian Frank on December 17, 2012 at 7:00am

Gruezi Hjalmar,

did you check the mesh for any open Edges, is it manifold? i think you will obtain nice and clean result only if you check your mesh first. Usually you can then just use the ordinary Mesh|Plane Component from GH in order to get these closed Curves (similar to those in your first sketch).

Do a mesh Check...it should say this:

Mesh does not have any degenerate faces.
Mesh does not have any extremely short edges.
Mesh does not have any non manifold edges.
Mesh does not have any duplicate faces.
Mesh does not have any faces with directions different from the mesh as a whole.
Mesh does not have any self intersecting faces.
Mesh does not have any disjoint pieces.
Mesh does not have any unused vertices.

If everything is alright with your mesh and it doesn't run anyway, can you place a sample of the mesh? There are a lot of issues if you have to write an algorithm for closing and cleaning up curves if intersection doesn't work...see this project...(this is done with nurbs though)

Permalink Reply by hjalmar schmid on December 18, 2012 at 10:06am

Grüessech!

It says the following thing if I do a meshcheck:

This is a good mesh.

Importants thing to consider with this mesh:
Mesh has 2124 naked edges. Although this does not necessarily mean that the mesh is bad,
naked edges can cause problems if the ultimate goal is STL output.

General information about this mesh:
Mesh does not have any degenerate faces.
Mesh does not have any zero length edges.
Mesh does not have any non manifold edges.
Mesh does not have any duplicate faces.
Mesh does not have any faces that could make it better if their directions were flipped.
Mesh has 8 disjoint pieces.
Mesh does not have any unused vertices.

Is the problem caused by the 8 disjoint pieces? Unfortunately the page with your link isn't there any more.

Thx for your help

Permalink Reply by Florian Frank on December 18, 2012 at 10:55am

Hm i think the 2124 naked edges are a lot more problematic naked edges usually results in open curves when cutting...You can try to run the MeshRepair in order to get rid of those disjoint pieces.

But if you place an example i can take a look at it...probably it's not worth it cleaning up the hole mesh...once you have some acceptable curves there are methods to get good closed polycurves from.

Good luck with the repair command in the meantime ;-)

Permalink Reply by hjalmar schmid on December 19, 2012 at 3:46am

Ok I tried MeshRepair, there are no disjoint pieces any more, but it didn't change anything. Could it be that the mesh is too complex? It was created from a pointcloud with the delaunay command from the pointsetreconstruction plug-in.

But if I use the common GH mesh|plane component instead of the C#script it works as you said)

It would be nice of corse to make a 100% running script, but in the worst case I could just do the curves manually with the GH component and feed the curves to the script.

If you nevertheless want to have a look at the file it is here:

http://www.file-upload.net/download-6946045/meshterrain.3dm.html

Thx so much for your great help

Best regards

Hjalmar

Permalink Reply by Florian Frank on December 19, 2012 at 6:36am

Hi hjalmar,

i took a quick look at your file. The terrain is ok but the cubes of the housings is crap. This creates the problems ... you have to redo that part with booling.

I suppose you got your data from swisstopo...check out my website: www.blickfeld7.com you can use the plugin called ASCII dgm if you have asc files in the future.

There is no need for delaunay command.

For this time i made you a nice clean (all quads) mesh terrain and a nurbs surface in case you need.

Here some self-explaining pics of the current problem:

This is the new mesh terrain...extrude your building a lot more into the ground this time ;-)