Checking a Closed Polyhedra!

Jankey · 2001-10-18T06:45:18

If i have a 3D Object And i want to know how i can check this object if it is "closed"? Does anyone hava an Idea how this could work?

Math and Physics Programming

Started by Jankey October 10, 2001 08:46 AM

11 comments, last by Jankey 23 years, 3 months ago

no way

122

October 17, 2001 11:16 PM

Ill just drop in my version as well

  void solidmesh::addEdge(int a,int b) {//check for exactly one a->b edge + one b->a edge	for (long i=0;i<numEdges;i++)		//b->a edge 		if (edges[i].vA == b && edges[i].vB == a) {			edges[i].ref++;			return;			}//one a->b edge	edges[numEdges].vA = a;	edges[numEdges].vB = b;	numEdges++;	}void solidmesh::buildEdges() {	//max amount of edges is Triangles*3	edges = (EDGE *) malloc(sizeof(EDGE) * numFaces * 3);	memset(edges,0,sizeof(EDGE) * numFaces * 3);	for (long i=0;i < numFaces ; i++ ) {		addEdge(face[i].a,face[i].b);		addEdge(face[i].b,face[i].c);		addEdge(face[i].c,face[i].a);		}	edges = (EDGE *) realloc(edges,sizeof(EDGE) * numEdges);	//check whether every edge occured twice	for (long i=0;i<numEdges;i++) assert(edges[i].ref == 1);	//eulers formula	assert(numVertices - numEdges + numFaces == 2 );	}

Jankey

Author

122

October 18, 2001 01:25 AM

wow, .. i have to make some speed ups in this code ( ms P3 667 Calculated a mesh about 3 Mins ( where where a few Thousands Of Triangles ...)) ...

J.A.N.K.E.Y.: Journeying Artificial Nocturnal Killing and Exploration Youth

no way

122

October 18, 2001 06:45 AM

notice that you have implemented an O(n2) algorithm here, eg. time taken to run the algorithm is proportional to square of number of polygons. No matter how you optimise the code, it will be slow on large poly counts.
My version should be slightly faster, something like O(n + n log E) where E is total number of edges on model.

BTW i think you have a typo here

  ....{tri[0] = object.pfaces.vertexIndex[0];tri[1] = object.pfaces[i].vertexIndex[1];....

Shouldnt it be

  ....{tri[0] = object.pfaces[i].vertexIndex[0];tri[1] = object.pfaces[i].vertexIndex[1];....

Checking a Closed Polyhedra!

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Checking a Closed Polyhedra!

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