Marching Cubes Terrassing/Ridge Effect
I am implementing a marching cubes algorithm generally based on the implementation of Paul Bourke with some major adjustments:
Basically I changed nearly 80% of his code. My resulting mesh has some ugly terrasses and I am not sure how to avoid them. I assumed that using floating points for the scalar field would do the job. Is this a common effect? How can you avoid it?
calculating the vertex positions on the edges. (cell.val[p1] contains the scalar value for the given vertex):
//if there is an intersection on this edge
if (cell.iEdgeFlags & (1 << iEdge))
{
const int* edge = a2iEdgeConnection[iEdge];
int p1 = edge[0];
int p2 = edge[1];
//find the approx intersection point by linear interpolation between the two edges and the density value
float length = cell.val[p1] / (cell.val[p2] + cell.val[p1]);
asEdgeVertex[iEdge] = cell.p[p1] + length * (cell.p[p2] - cell.p[p1]);
}
You can find the complete sourcecode here: https://github.com/DieOptimistin/MarchingCubes I use Ogre3D as library for this example.
As Andy Newmann said, the devil was in the linear interpolation. Correct is:
float offset;
float delta = cell.val[p2] - cell.val[p1];
if (delta == 0) offset = 0.5;
else offset = (mTargetValue - cell.val[p1]) / delta;
asEdgeVertex[iEdge] = cell.p[p1] + offset* (cell.p[p2] - cell.p[p1]);