Picking mesh elements that are not on the border of the mesh












5














As an example, let's say I use a set of random points to create a Voronoi mesh



pts = RandomReal[{-1, 1}, {100, 2}];

VoronoiMesh[pts, {-1, 1}]


and get something that looks like this:



enter image description here



My question is: Is there an efficient way to determine which of the regions (mesh elements, whatever you call them) are not touching the edge of the mesh? I know that there are a lot of built in functions that give properties of elements in a mesh, but I am unfamiliar with them, and I can't seem to find an efficient way to do this beyond "looping" through all elements and just picking which elements do not have points that touch the edge.






performance-tuning mesh







share|improve this question






















  • RegionBoundary? To get coordinates you can do RegionBoundary@mesh // MeshCoordinates
    – b3m2a1
    4 hours ago












  • @b3m2a1 I mean to find the "shapes" that are not touching the outside. I don't need the coordinates of the outer edge.
    – Aaron Stevens
    4 hours ago










  • Ah I did a lazy read through and figured you wanted the boundary. Always possible to take a complement with the boundary cells, though, to get the interior.
    – b3m2a1
    4 hours ago
















5














As an example, let's say I use a set of random points to create a Voronoi mesh



pts = RandomReal[{-1, 1}, {100, 2}];

VoronoiMesh[pts, {-1, 1}]


and get something that looks like this:



enter image description here



My question is: Is there an efficient way to determine which of the regions (mesh elements, whatever you call them) are not touching the edge of the mesh? I know that there are a lot of built in functions that give properties of elements in a mesh, but I am unfamiliar with them, and I can't seem to find an efficient way to do this beyond "looping" through all elements and just picking which elements do not have points that touch the edge.






performance-tuning mesh







share|improve this question






















  • RegionBoundary? To get coordinates you can do RegionBoundary@mesh // MeshCoordinates
    – b3m2a1
    4 hours ago












  • @b3m2a1 I mean to find the "shapes" that are not touching the outside. I don't need the coordinates of the outer edge.
    – Aaron Stevens
    4 hours ago










  • Ah I did a lazy read through and figured you wanted the boundary. Always possible to take a complement with the boundary cells, though, to get the interior.
    – b3m2a1
    4 hours ago














5












5








5







As an example, let's say I use a set of random points to create a Voronoi mesh



pts = RandomReal[{-1, 1}, {100, 2}];

VoronoiMesh[pts, {-1, 1}]


and get something that looks like this:



enter image description here



My question is: Is there an efficient way to determine which of the regions (mesh elements, whatever you call them) are not touching the edge of the mesh? I know that there are a lot of built in functions that give properties of elements in a mesh, but I am unfamiliar with them, and I can't seem to find an efficient way to do this beyond "looping" through all elements and just picking which elements do not have points that touch the edge.






performance-tuning mesh







share|improve this question













As an example, let's say I use a set of random points to create a Voronoi mesh



pts = RandomReal[{-1, 1}, {100, 2}];

VoronoiMesh[pts, {-1, 1}]


and get something that looks like this:



enter image description here



My question is: Is there an efficient way to determine which of the regions (mesh elements, whatever you call them) are not touching the edge of the mesh? I know that there are a lot of built in functions that give properties of elements in a mesh, but I am unfamiliar with them, and I can't seem to find an efficient way to do this beyond "looping" through all elements and just picking which elements do not have points that touch the edge.






performance-tuning mesh




performance-tuning mesh






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked 5 hours ago









Aaron StevensAaron Stevens

299110




299110












  • RegionBoundary? To get coordinates you can do RegionBoundary@mesh // MeshCoordinates
    – b3m2a1
    4 hours ago












  • @b3m2a1 I mean to find the "shapes" that are not touching the outside. I don't need the coordinates of the outer edge.
    – Aaron Stevens
    4 hours ago










  • Ah I did a lazy read through and figured you wanted the boundary. Always possible to take a complement with the boundary cells, though, to get the interior.
    – b3m2a1
    4 hours ago


















  • RegionBoundary? To get coordinates you can do RegionBoundary@mesh // MeshCoordinates
    – b3m2a1
    4 hours ago












  • @b3m2a1 I mean to find the "shapes" that are not touching the outside. I don't need the coordinates of the outer edge.
    – Aaron Stevens
    4 hours ago










  • Ah I did a lazy read through and figured you wanted the boundary. Always possible to take a complement with the boundary cells, though, to get the interior.
    – b3m2a1
    4 hours ago
















RegionBoundary? To get coordinates you can do RegionBoundary@mesh // MeshCoordinates
– b3m2a1
4 hours ago






RegionBoundary? To get coordinates you can do RegionBoundary@mesh // MeshCoordinates
– b3m2a1
4 hours ago














@b3m2a1 I mean to find the "shapes" that are not touching the outside. I don't need the coordinates of the outer edge.
– Aaron Stevens
4 hours ago




@b3m2a1 I mean to find the "shapes" that are not touching the outside. I don't need the coordinates of the outer edge.
– Aaron Stevens
4 hours ago












Ah I did a lazy read through and figured you wanted the boundary. Always possible to take a complement with the boundary cells, though, to get the interior.
– b3m2a1
4 hours ago




Ah I did a lazy read through and figured you wanted the boundary. Always possible to take a complement with the boundary cells, though, to get the interior.
– b3m2a1
4 hours ago










2 Answers
2






active

oldest

votes


















4














vm = VoronoiMesh[pts, {-1, 1}]

HighlightMesh[vm, MeshCellIndex[vm, {2, "Interior"}]]


enter image description here



Related: Boundary cells of a mesh?



Show[vm, Epilog -> {Opacity[.7, Orange], MeshPrimitives[vm, {2, "Interior"}]}]


enter image description here






share|improve this answer























  • Yep that was the simple answer I was expecting haha. Thanks!
    – Aaron Stevens
    4 hours ago










  • @kglr Wow, I'm impressed. Where did you find this syntax? The doc page of MeshCellIndex does not show it as example...
    – Henrik Schumacher
    4 hours ago










  • @HenrikSchumacher, blind search trying some objects returned by vm["Properties"]:)
    – kglr
    3 hours ago



















5














For planar MeshRegion that arise from DelaunayMesh or VoronoiMesh, usually



R["InteriorFaces"]


should work.



A more general and more transparent ways is to use the package "IGraphM`" by Szabolcs as follows:



Needs["IGraphM`"]



A = IGMeshCellAdjacencyMatrix[R, 1, 2];

bndedges = Random`Private`PositionsOf[Total[A, {2}], 1];

interiorfaces = Random`Private`PositionsOf[Total[A[[bndedges]]], 0];



HighlightMesh[R, Thread[{2, interiorfaces}]]


enter image description here






share|improve this answer





















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    2 Answers
    2






    active

    oldest

    votes








    2 Answers
    2






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    4














    vm = VoronoiMesh[pts, {-1, 1}]
    
HighlightMesh[vm, MeshCellIndex[vm, {2, "Interior"}]]


    enter image description here



    Related: Boundary cells of a mesh?



    Show[vm, Epilog -> {Opacity[.7, Orange], MeshPrimitives[vm, {2, "Interior"}]}]


    enter image description here






    share|improve this answer























    • Yep that was the simple answer I was expecting haha. Thanks!
      – Aaron Stevens
      4 hours ago










    • @kglr Wow, I'm impressed. Where did you find this syntax? The doc page of MeshCellIndex does not show it as example...
      – Henrik Schumacher
      4 hours ago










    • @HenrikSchumacher, blind search trying some objects returned by vm["Properties"]:)
      – kglr
      3 hours ago
















    4














    vm = VoronoiMesh[pts, {-1, 1}]
    
HighlightMesh[vm, MeshCellIndex[vm, {2, "Interior"}]]


    enter image description here



    Related: Boundary cells of a mesh?



    Show[vm, Epilog -> {Opacity[.7, Orange], MeshPrimitives[vm, {2, "Interior"}]}]


    enter image description here






    share|improve this answer























    • Yep that was the simple answer I was expecting haha. Thanks!
      – Aaron Stevens
      4 hours ago










    • @kglr Wow, I'm impressed. Where did you find this syntax? The doc page of MeshCellIndex does not show it as example...
      – Henrik Schumacher
      4 hours ago










    • @HenrikSchumacher, blind search trying some objects returned by vm["Properties"]:)
      – kglr
      3 hours ago














    4












    4








    4






    vm = VoronoiMesh[pts, {-1, 1}]
    
HighlightMesh[vm, MeshCellIndex[vm, {2, "Interior"}]]


    enter image description here



    Related: Boundary cells of a mesh?



    Show[vm, Epilog -> {Opacity[.7, Orange], MeshPrimitives[vm, {2, "Interior"}]}]


    enter image description here






    share|improve this answer














    vm = VoronoiMesh[pts, {-1, 1}]
    
HighlightMesh[vm, MeshCellIndex[vm, {2, "Interior"}]]


    enter image description here



    Related: Boundary cells of a mesh?



    Show[vm, Epilog -> {Opacity[.7, Orange], MeshPrimitives[vm, {2, "Interior"}]}]


    enter image description here







    share|improve this answer














    share|improve this answer



    share|improve this answer








    edited 4 hours ago

























    answered 4 hours ago









    kglrkglr

    177k9198408




    177k9198408












    • Yep that was the simple answer I was expecting haha. Thanks!
      – Aaron Stevens
      4 hours ago










    • @kglr Wow, I'm impressed. Where did you find this syntax? The doc page of MeshCellIndex does not show it as example...
      – Henrik Schumacher
      4 hours ago










    • @HenrikSchumacher, blind search trying some objects returned by vm["Properties"]:)
      – kglr
      3 hours ago


















    • Yep that was the simple answer I was expecting haha. Thanks!
      – Aaron Stevens
      4 hours ago










    • @kglr Wow, I'm impressed. Where did you find this syntax? The doc page of MeshCellIndex does not show it as example...
      – Henrik Schumacher
      4 hours ago










    • @HenrikSchumacher, blind search trying some objects returned by vm["Properties"]:)
      – kglr
      3 hours ago
















    Yep that was the simple answer I was expecting haha. Thanks!
    – Aaron Stevens
    4 hours ago




    Yep that was the simple answer I was expecting haha. Thanks!
    – Aaron Stevens
    4 hours ago












    @kglr Wow, I'm impressed. Where did you find this syntax? The doc page of MeshCellIndex does not show it as example...
    – Henrik Schumacher
    4 hours ago




    @kglr Wow, I'm impressed. Where did you find this syntax? The doc page of MeshCellIndex does not show it as example...
    – Henrik Schumacher
    4 hours ago












    @HenrikSchumacher, blind search trying some objects returned by vm["Properties"]:)
    – kglr
    3 hours ago




    @HenrikSchumacher, blind search trying some objects returned by vm["Properties"]:)
    – kglr
    3 hours ago











    5














    For planar MeshRegion that arise from DelaunayMesh or VoronoiMesh, usually



    R["InteriorFaces"]


    should work.



    A more general and more transparent ways is to use the package "IGraphM`" by Szabolcs as follows:



    Needs["IGraphM`"]
    

    
A = IGMeshCellAdjacencyMatrix[R, 1, 2];
    
bndedges = Random`Private`PositionsOf[Total[A, {2}], 1];
    
interiorfaces = Random`Private`PositionsOf[Total[A[[bndedges]]], 0];
    

    
HighlightMesh[R, Thread[{2, interiorfaces}]]


    enter image description here






    share|improve this answer


























      5














      For planar MeshRegion that arise from DelaunayMesh or VoronoiMesh, usually



      R["InteriorFaces"]


      should work.



      A more general and more transparent ways is to use the package "IGraphM`" by Szabolcs as follows:



      Needs["IGraphM`"]
      

      
A = IGMeshCellAdjacencyMatrix[R, 1, 2];
      
bndedges = Random`Private`PositionsOf[Total[A, {2}], 1];
      
interiorfaces = Random`Private`PositionsOf[Total[A[[bndedges]]], 0];
      

      
HighlightMesh[R, Thread[{2, interiorfaces}]]


      enter image description here






      share|improve this answer
























        5












        5








        5






        For planar MeshRegion that arise from DelaunayMesh or VoronoiMesh, usually



        R["InteriorFaces"]


        should work.



        A more general and more transparent ways is to use the package "IGraphM`" by Szabolcs as follows:



        Needs["IGraphM`"]
        

        
A = IGMeshCellAdjacencyMatrix[R, 1, 2];
        
bndedges = Random`Private`PositionsOf[Total[A, {2}], 1];
        
interiorfaces = Random`Private`PositionsOf[Total[A[[bndedges]]], 0];
        

        
HighlightMesh[R, Thread[{2, interiorfaces}]]


        enter image description here






        share|improve this answer












        For planar MeshRegion that arise from DelaunayMesh or VoronoiMesh, usually



        R["InteriorFaces"]


        should work.



        A more general and more transparent ways is to use the package "IGraphM`" by Szabolcs as follows:



        Needs["IGraphM`"]
        

        
A = IGMeshCellAdjacencyMatrix[R, 1, 2];
        
bndedges = Random`Private`PositionsOf[Total[A, {2}], 1];
        
interiorfaces = Random`Private`PositionsOf[Total[A[[bndedges]]], 0];
        

        
HighlightMesh[R, Thread[{2, interiorfaces}]]


        enter image description here







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered 4 hours ago









        Henrik SchumacherHenrik Schumacher

        49.8k469142




        49.8k469142






























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