[OpenFOAM] Distance between STL and mesh

axtone · August 2, 2025, 09:58

After creating a mesh with Snappyhexmesh, I want to analyze the differences between the resulting mesh and the original STL geometry (such as the distance between the snapped mesh and the STL). If the mesh does not fit perfectly on the surface and there are slight irregularities, I want to analyze these. How can I do this?

ABitShy · August 17, 2025, 08:38

Quote:

Originally Posted by axtone

After creating a mesh with Snappyhexmesh, I want to analyze the differences between the resulting mesh and the original STL geometry (such as the distance between the snapped mesh and the STL). If the mesh does not fit perfectly on the surface and there are slight irregularities, I want to analyze these. How can I do this?

Is there a specific mesh issue you are facing?

From experience, with suitable mesh size controls, you can control the irregularities within your expectations.

Otherwise, scripts can loop the coordinates of each face mesh cell of specified problematic faces. This in turn can be used to interpolate the coordinates of the STL geometric faces and compute the distance differences. A distribution of mesh distance errors can be calculated from this for easy reference.

Regards,
Ewan

axtone · August 17, 2025, 09:13

I was wondering about the distance between the STL file and the snapped mesh. Some sections of my mesh have minor indentations or bulges. I'd like to know the local deflection values. However, I haven't been able to write the script, so any help would be greatly appreciated.

AtoHM · September 16, 2025, 12:21

I dont know exactly how it will work, but I would try to figure out the boundary nodes of the mesh from the polyMesh folder and compute somehow the distance to the appropriate part of the stl. A problem comes to mind: stl is tessellated and huge faces are probably meshed by thousands of finite faces. So you cannot compute the distance to the nodes of the stl file (well, you can, but it does not tell you anything). You need to compute the shortest distances to each face of the stl, which you must describe first, mathematically. Possible, but an additional step to consider. Corners might pose additional problems.

.. and then, you have the total deviation at each mesh node. I wonder how that is helping you?

August 2, 2025, 09:58	Distance between STL and mesh	#1
axtone New Member Join Date: Jul 2025 Posts: 4 Rep Power: 2	After creating a mesh with Snappyhexmesh, I want to analyze the differences between the resulting mesh and the original STL geometry (such as the distance between the snapped mesh and the STL). If the mesh does not fit perfectly on the surface and there are slight irregularities, I want to analyze these. How can I do this?

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August 17, 2025, 09:13		#3
axtone New Member Join Date: Jul 2025 Posts: 4 Rep Power: 2	I was wondering about the distance between the STL file and the snapped mesh. Some sections of my mesh have minor indentations or bulges. I'd like to know the local deflection values. However, I haven't been able to write the script, so any help would be greatly appreciated.

September 16, 2025, 12:21		#4
AtoHM Senior Member M Join Date: Dec 2017 Posts: 730 Rep Power: 14	I dont know exactly how it will work, but I would try to figure out the boundary nodes of the mesh from the polyMesh folder and compute somehow the distance to the appropriate part of the stl. A problem comes to mind: stl is tessellated and huge faces are probably meshed by thousands of finite faces. So you cannot compute the distance to the nodes of the stl file (well, you can, but it does not tell you anything). You need to compute the shortest distances to each face of the stl, which you must describe first, mathematically. Possible, but an additional step to consider. Corners might pose additional problems. .. and then, you have the total deviation at each mesh node. I wonder how that is helping you?