How to use fix Tunnels

[leye123]

I am trying to detect tunnels in a mesh using detectTunnelFaces. To test the function, I generated the following code:
`

mesh_path = './upper_model.stl'
mesh = mm.loadMesh(mesh_path)
metric = mm.edgeCurvMetric(mesh, 2)
setting = mm.DetectTunnelSettings()
setting.maxIters = 5
setting.maxTunnelLength = 10000
setting.filterEquivalentCoLoops = True
setting.buildCoLoops = True
setting.metric = metric
tunnels = mm.detectTunnelFaces(mesh, setting)
mm.expand(mesh.topology, tunnels, 5)
mesh.deleteFaces(tunnels)

`

I tried looking for the corresponding metric, but couldn't find it. How should I go about finding tunnels using the appropriate type?

[Fedr]

Please use the metrics as follows.

Shortest:

metric = edgeLengthMetric( mesh );

Most Curved:

metric = edgeAbsCurvMetric( mesh, -angleSinFactor );

Most Concave:

metric = edgeCurvMetric( mesh, angleSinFactor );

Most Convex:

metric = edgeCurvMetric( mesh, -angleSinFactor );

Least Curved:

metric = edgeAbsCurvMetric( mesh, angleSinFactor );

[leye123]

Thank you for your reply!
But I found that using fix Tunnels can lead to unexpected results. How should I deal with this situation? Green is the area I need, red is what's detected. Using these types, it's hard to control the parameters.

upper_model.zip

[Fedr]

Every tunnel on the mesh has two associated not-trivial (not-collapsible) co-loops. On your picture one is red, and the other one is green.

MeshLib has a function to find one such loop given its associated loop:

/// given not-separating loop on input, finds the loop (also not-separation) that
/// 1) goes from left side of input loop
/// 2) returns to the input loop from its right side
/// 3) goes along the input loop to become closed
/// such that the resulting loop has minimal sum of given metric for its edges;
/// edges 1) and 2) can be only inner or boundary to the given region (they must have region from left or from right)
MRMESH_API Expected<EdgeLoop> findSmallestMetricCoLoop( const MeshTopology& topology, const EdgeLoop& loop, const EdgeMetric& metric,
    const FaceBitSet* region = nullptr );

/// same as \ref findMinimalCoLoop with euclidean edge length metric
MRMESH_API Expected<EdgeLoop> findShortestCoLoop( const MeshPart& mp, const EdgeLoop& loop );

In you example, the co-loop is shorter, so the fix in #6305 will find it:

But if you want to find not the shortest not-collapsible loops, that always the ones around the tunnel, then you should select between co-loops on your side, e.g. testing which one has central point outside of mesh.

[leye123]

Thanks for your answer. Does this mean it will be available as an option to turn on in the next update?

[Fedr]

Yes, we include the improvement in the nearest release.