How to fix the following errors:
- This surface is non-manifold, its inside can not be distinguished from its outside so its use within your project will be limited.
- This mesh has self-intersecting triangles.
Answers
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In Leapfrog Geo, a non-manifold issue with meshes refers to a situation where the mesh is not properly connected or has irregularities that prevent it from being a continuous, solid object. Non-manifold geometry can occur when mesh edges or vertices intersect in unexpected ways, creating gaps, overlaps, or disconnected regions. These issues can lead to inaccuracies in geological modeling and visualisation. Resolving non-manifold problems typically involves adjusting the mesh parameters or refining the input data to ensure a seamless and coherent representation of the geological features.
There is a small section on Manifold meshes in our help menu for imported meshes - https://help.seequent.com/Geo/2023.2/en-GB/Content/meshes/mesh-issues.htm?Highlight=manifold#edges
Meshes imported or created in Leapfrog Geo may exhibit geometries that cannot be used computationally by Leapfrog Geo. Leapfrog Geo can identify and work with certain situations, such as non-manifold meshes with shared edges with an even number of adjoining triangles, and for other cases Leapfrog Geo provides some tools that may fix some meshes.
Depending on the error type and number you can determine what steps you need to do.
There are two types of manifold errors (see example in the image below). These were introduced in 2021 can be validated and you can continue processes as normal. And one you need to rectify before proceeding.
- We can happily use meshes in our operations that have shared triangles edges that have an even number of triangles sharing the edge = "good" non-manifold edge
- We cannot use meshes that have edges that have shared triangles edges that have an odd number of triangles sharing the edge = "odd" non-manifold edge
If the error type is “Mesh issues with odd non-multiple edges” you will need to drag these into the scene, review and correct these in the original mesh.
Your first step is to visualise the issues. In the Meshes folder, you can expand the Mesh to see the location and type of errors that are present. If they are an imported mesh, you should be able to visualise them in the scene, by dragging and dropping. I recommend clearing the scene first as they are often quite small lines.
They should also be available now under the Geological model, or they can be extracted from the output volume into the Meshes folder, so you can see the location of the mesh error.
Numeric models don’t display the output volume errors, so they need to be extracted first.
- Right click the 3cm output volume > Extract Mesh > Mesh Parts
- Ensure to select all the mesh components.
The Cleanup Mesh window has a Remove self-intersections for volumes option that can be useful in fixing some self intersections. The Cleanup Mesh window can be opened by double-clicking on an imported mesh in the project tree. Read more here: https://help.seequent.com/Geo/2022.1/en-GB/Content/meshes/mesh-issues.htm
Fixing meshes can be done by editing the original mesh surface (in the surface chronology) in the error location using points or polylines to adjust the mesh and remove the error.
- Ensure they are using the latest version. We have worked hard over the last few releases to improve the generation of output volumes, improve visualisation of mesh errors and will continue to improve this in the future as well. However, it is often unavoidable when using any 3D modelling program.
- Sometimes changing the surface resolution can work (sometimes only changing by 1 or 2 can make a difference)
- Sometimes turning Adaptive off can work
- Sometimes turning snapping off works
- Change the Volume Generation of the GM, change between the No Merging, Fast and Robust setting.
- Sometimes reviewing the input data to the surface and removing conflicting information works.
- Making a small edit (point, polyline, structural disc) to one or more surfaces even a small degree can help remove the issue
- For imported mesh, sometimes create a distance buffer with a very small buffer size around the mesh can help create a new valid mesh
There is no one single recommendation we can make that will magically fix all manifold issues. It’s a test and trial method.
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Depending on how complex your mesh is you can use the distance function to help correct manifold and self intersections.
Create a distance function from the problem mesh. Generate a buffer at 1 with a 0.5 resolution. Make sure that you set the buffer to treat closed surfaces as: Surfaces.
Extract the mesh part for the outer surface of the distance buffer. This will be the positive surface when you extract mesh parts.
Now repeat the original 1m distance buffer but this time do it based on the previous extracted surface that you made. This will shift the mesh back to the location of the original mesh but with no issues.
Note that some sharp corners will be rounded and very thin meshes it will not work well but it is the best method I have found for cleaning up problem meshes that have been imported from other sources.
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