};
/** march iterates over the entire dataset, calling vMarchCube on each cube */
- public static void march(SampledField sampledField, double targetValue, int iDataSetSize, double fStepSize, Mesh mesh) {
+ public static void march(SampledField sampledField, double threshold, int iDataSetSize, double fStepSize, Mesh mesh) {
int iX, iY, iZ;
int initialTriangles = mesh.numTriangles();
for(iX = 0; iX < iDataSetSize; iX++) {
(mesh.numTriangles()-initialTriangles) + " triangles");
for(iY = 0; iY < iDataSetSize; iY++)
for(iZ = 0; iZ < iDataSetSize; iZ++)
- march(sampledField, mesh, targetValue, iX*fStepSize, iY*fStepSize, iZ*fStepSize, fStepSize);
+ march(sampledField, mesh, threshold, iX*fStepSize, iY*fStepSize, iZ*fStepSize, fStepSize);
}
System.out.print("\r");
for(int i=0; i<78; i++) System.out.print(' ');
}
/** performs the Marching Cubes algorithm on a single cube */
- static void march(SampledField sampledField, Mesh mesh, double targetValue, double fX, double fY, double fZ, double fScale) {
+ static void march(SampledField sampledField, Mesh mesh, double threshold, double fX, double fY, double fZ, double fScale) {
int iCorner, iVertex, iVertexTest, iEdge, iTriangle, iFlagIndex, iEdgeFlags;
double fOffset;
GLvector sColor;
// Find which vertices are inside of the surface and which are outside
iFlagIndex = 0;
- for(iVertexTest = 0; iVertexTest < 8; iVertexTest++) {
- if (afCubeValue[iVertexTest] <= targetValue) {
+ for(iVertexTest = 0; iVertexTest < 8; iVertexTest++)
+ if (afCubeValue[iVertexTest] >= threshold)
iFlagIndex |= 1<<iVertexTest;
- }
- }
// Find which edges are intersected by the surface
iEdgeFlags = aiCubeEdgeFlags[iFlagIndex];
// If there is an intersection on this edge
if ((iEdgeFlags & (1<<iEdge))==0) continue;
fOffset = fGetOffset(afCubeValue[ a2iEdgeConnection[iEdge][0] ],
- afCubeValue[ a2iEdgeConnection[iEdge][1] ], targetValue);
+ afCubeValue[ a2iEdgeConnection[iEdge][1] ],
+ threshold,
+ fScale * 0.1);
asEdgeVertex[iEdge].fX = fX + (a2fVertexOffset[ a2iEdgeConnection[iEdge][0] ][0] + fOffset * a2fEdgeDirection[iEdge][0]) * fScale;
asEdgeVertex[iEdge].fY = fY + (a2fVertexOffset[ a2iEdgeConnection[iEdge][0] ][1] + fOffset * a2fEdgeDirection[iEdge][1]) * fScale;
iVertex = a2iTriangleConnectionTable[iFlagIndex][3*iTriangle+iCorner];
points[iCorner] = new Point(asEdgeVertex[iVertex].fX, asEdgeVertex[iVertex].fY, asEdgeVertex[iVertex].fZ);
- // questionable
+ // questionable, but we do it anyways
norm = norm.plus(new Vec(asEdgeNorm[iVertex].fX, asEdgeNorm[iVertex].fY, asEdgeNorm[iVertex].fZ));
}
- if (points[0].equals(points[1])) continue;
- if (points[0].equals(points[2])) continue;
- if (points[1].equals(points[2])) continue;
- mesh.newT(points[0], points[1], points[2], norm.norm(), 1);
+
+ // Eliminate triangles with "length-zero" sides.
+ // Unfortunately this puts holes in the mesh.
+ if (points[0].equals(points[1]) ||
+ points[0].equals(points[2]) ||
+ points[1].equals(points[2]))
+ continue;
+
+ mesh.newT(points[0], points[1], points[2], norm.norm().times(-1));
}
}
// fGetOffset finds the approximate point of intersection of the surface
// between two points with the values fValue1 and fValue2
- static double fGetOffset(double fValue1, double fValue2, double fValueDesired) {
+ static double fGetOffset(double fValue1, double fValue2, double fValueDesired, double EPSILON) {
double fDelta = fValue2 - fValue1;
if(fDelta == 0.0) return 0.5;
+
+ // the following two lines are a hack; they "snap" the
+ // estimate to one grid point or the other if the distance is
+ // less than some EPSILON. This ensures that the resulting
+ // mesh is watertight and meets the requirements of Mesh.java
+ if (Math.abs(fValueDesired-fValue1) < EPSILON) return 0;
+ if (Math.abs(fValueDesired-fValue2) < EPSILON) return 1;
+
return (fValueDesired - fValue1)/fDelta;
}