How are rays working?

Troubleshooting General Help
1

Hi everybody,
i have some issues with raycasting. In my programm I shoot rays from different points in the 6 main directions (0,0,1), (0,0,-1), …, (-1, 0, 0). I set their limit to 1. Given an origin and an obviously normalized direction. I still get results where getDistance() gives values > 1. The way I would interpret setLimit is that it would ignore all results that are farther away then direction * limit. But it seems like it is not.

Can anyone tell why that is? Or how its actually working?

Thx
Greetz Xeratos

2

You’d have to show us the code. Limit should limit the results… it always does for me.

3

Hmm ok consider this mesh. A 3x3 grid with distance 1:

Now I shoot the rays from each of these points in 6 directions as mentioned above:

[java]
public static Vector3f[] rDirections = new Vector3f[] { new Vector3f(0, 0, 1),
new Vector3f(0, 0, -1),
new Vector3f(1, 0, 0),
new Vector3f(-1, 0, 0),
new Vector3f(0, 1, 0),
new Vector3f(0, -1, 0) }

public float extractVoxelData2(Geometry refGeom, Vector3f voxelPos) {
float[] densities0, densities1;
CollisionResults tmpResults = new CollisionResults();
CollisionResult r;

    Ray ray = new Ray();
    ray.setLimit(1);
    for (Vector3f rDirection : rDirections) {
        tmpResults.clear();

        ray.setOrigin(voxelPos);
        ray.setDirection(rDirection);
        refGeom.collideWith(ray, tmpResults);

        for (int i = 0; i < tmpResults.size(); i++) {
            r = tmpResults.getCollision(i);
            // dbl = false;
            // if (results.size() > 0)
            // if (r.getContactPoint()
            // .equals(results.getCollision(results.size() - 1).getContactPoint())
            // && r.getDistance() == results.getCollision(results.size() - 1)
            // .getDistance()) {
            // dbl = true;
            // }
            // if (r.getDistance() <= 1 && !dbl) {
            results.addCollision(r);
            // } else {
            // // results.d
            // }
        }
    }

    if (results.size() > 0) {
        System.out.println("Results for " + voxelPos);
        densities0 = new float[results.size()];
        densities1 = new float[results.size()];
        for (int i = 0; i < results.size(); i++) {
            r = results.getCollision(i);

            densities0[0] = r.getDistance();
            densities1[0] = r.getDistance();

            System.out.println("Result " + i + ": contact " + r.getContactPoint()
                               + ",\n          normal " + r.getContactNormal()
                               + ",\n          distance " + r.getDistance()
                               + ", triIndex " + r.getTriangleIndex()
                               + ", tri distance "
                               + r.getTriangle(null).getCenter().distance(voxelPos));
            System.out.println();
        }
        System.out.println("----------------------------------");
    }

    return .5f;

}
[/java]

With this code I get 8 results for the 6 points outside the mesh and 24 for the one inside the mesh.
I get why its 4 cause it hits 4 triangles … but the others ofcourse also 4 but with distance 1.5f which would be fine if I wouldnt set a limit.