MeshVertexToplogy

[maxi]

Hi,

I am trying to get my head around what looks to be the incredibly powerful MeshTopologyVertex and Edge methods in rhinocommon. Essentially I want to export a mesh with CCW radially ordered vertices to text file. However I am getting some scrambled results - it appears (on checking on some simple mesh configs) that I am not implementing the ConnectedTopologyVertices() correctly as some vertices have obviously strange connection. Code snippet is as follows:

Python Code:

def exportMeshTopology():
 
    """GET MESH OBJECT IDENTIFIER"""
    rc, objref = Rhino.Input.RhinoGet.GetOneObject("Select MESH", False, Rhino.DocObjects.ObjectType.Mesh)
    if rc!=Rhino.Commands.Result.Success: return
 
    meshID  = scriptcontext.doc.Objects.Find(objref.ObjectId)
    meshObj = meshID.Geometry
 
    """SETUP EXPORT TEXT FILE"""
    filter = "Text File (*.txt)|*.txt|All Files (*.*)|*.*||"
    filename = rs.SaveFileName("Gimme a destination FILENAME", filter)
    if( filename==None ): return
    output = open( filename, "w" )
   
    """PROCESS MESH"""
    meshObj.Compact()
    meshObj.Normals.ComputeNormals()
   
    mVs  = meshObj.Vertices
    mNs  = meshObj.Normals
    mFs  = meshObj.Faces
    mEs  = meshObj.TopologyEdges
    mVTs = meshObj.TopologyVertices
    mVTs.SortEdges()
 
    """EXPORT VERTICES & VERTEX DATA"""
    for i in range( mVTs.Count ):
        # vertex id
        vIndex       = mVTs.TopologyVertexIndex(i)
        vConnections = mVTs.ConnectedTopologyVertices(i)
        # text file header
        strVtxHeader = "#VERTEX "   + str( vIndex )
        # vtx coordinates
        strVtxCoord  = "vCoord "    + str(mVs[vIndex].X) +","+ str(mVs[vIndex].Y) +","+ str(mVs[vIndex].Z)
        # vtx normal
        strVtxNormal = "vNormal "   + str(mNs[vIndex].X) +","+ str(mNs[vIndex].Y) +","+ str(mNs[vIndex].Z)
        # solve connected faces
        strVtxFaces  = "vFaces "
        conFaces     = mVTs.ConnectedFaces(i)
        for j in range(conFaces.Count):
            if(j==0):
                strVtxFaces = strVtxFaces + str(conFaces[j])
            else:
                strVtxFaces = strVtxFaces +"//"+ str(conFaces[j])
        # solve vertex topology
        strVtxTopo   = "vTopo "
        for k in range(vConnections.Count):
            if(k==0):
                strVtxTopo = strVtxTopo + str(vConnections[k])
            else:
                strVtxTopo = strVtxTopo +"//"+ str(vConnections[k])
               
        # export data
        output.write( strVtxHeader +" "+ strVtxCoord +" "+ strVtxNormal +" "+ strVtxFaces +" "+ strVtxTopo + "\n"   )
        rs.AddTextDot(strVtxHeader +"__"+ strVtxFaces +"__"+ strVtxTopo, mVs[vIndex] )
 
    """EXPORT FACES & FACEDATA"""
    for i in range(mFs.Count):
        strFaceHeader = "#FACE " + str(i)
        strFaceVtcs   = "Vtcs " + str(mFs[i].A) +"//"+ str(mFs[i].B) +"//"+ str(mFs[i].C) +"//"+ str(mFs[i].D)
        eSet          = mEs.GetEdgesForFace(i)
        strEdgeSet    = "Edges "
        arrPtCentroid = averagePoints( [ mVs[mFs[i].A], mVs[mFs[i].B], mVs[mFs[i].C], mVs[mFs[i].D] ] )
        for m in range( eSet.Count ):
            if(m==0): strEdgeSet = strEdgeSet + str(eSet[m])
            else:     strEdgeSet = strEdgeSet +"//"+ str(eSet[m])
        # notate
        rs.AddTextDot( str(i) +"__"+ strFaceVtcs +"__"+ strEdgeSet, arrPtCentroid )
        # export data
        output.write(strFaceHeader +" "+ strFaceVtcs +" "+ strEdgeSet + "\n")
 
    output.flush()
    output.close()
 
def averagePoints(PTS):
    count = 0
    sum   = Rhino.Geometry.Point3d(0,0,0)
    for i in range(PTS.Count):
        sum = Rhino.Geometry.Point3d.Add(sum, PTS[i])
        count+=1
    avg   = Rhino.Geometry.Point3d.Divide(sum, count)
    return avg
 
if( __name__ == "__main__" ):
    exportMeshTopology()

[Steve Baer]

Topology vertices represent a single location in space. There may be multiple regular mesh vertices for any given topology vertex. If you are trying to just export a list of faces and vertex locations for each face then you don't need the topology stuff at all.

[maxi]

Hi Steve,

Assuming the mesh is valid and has no duplicate vertices and that exporting vertices and faces (using rhinoscriptsyntax or rhinocommon) is no problem. What I want to achieve is an understanding of all the topological connections (edges and the vertices at the other end of these edges), ordered counter-clockwise, for each vertex of an arbitrary mesh. The vertex/edge topology is critical for latter fluid vector fields I am building across an arbitrary (unordered) mesh.

[Steve Baer]

One piece of code that jumps out at me is the line

Python Code:

for i in range( mVTs.Count ):
    # vertex id
    vIndex       = mVTs.TopologyVertexIndex(i)

TopologyVertexIndex finds the corresponding index in the TopologyVertices list for a given index of a vertex in the Vertices list. If you want the location of the TopologyVertex, then you can just rewrite your script as

Python Code:

for i in range( mVTs.Count ):
    coordinate = mVTs[i]
    ...

I'm not sure that is what you're after though since you are then trying to export the normal. A TopologyVertex may have multiple vertices associated with it and therefore multiple normals. There is a one-to-one association of vertices and normals, but there can be a many-to-one association of vertices to topology vertices.

I hope I'm being somewhat clear; it is a hard topic to describe without making some pictures.
-Steve