classify point

Depends on how you calculated the intercept, and whether you already negated it or not. Usually, if you just took the dot product between the normal and a point on the plane to find it, you would subtract later on, but if you negated it already then you add. Experiment a bit to see which one gives you the right direction.

Also, 0.01 might be a tad big for an epsilon value. You might also try tweaking that if you get too many points on the plane.

[edited by - Fantasio on March 4, 2004 11:23:34 AM]

Determining if a point is visible to a plane comes from the plane equation:

Ax + By + Cz + D = 0
P.N + D = 0
D = -P.N

So, D is the negative DotProduct of your test point and the plane's normal.

Did you grab that example from some demo source code, like Pauls Project's? He has a function like that uses the word 'intercept':


void CalculateIntercept(const VECTOR3D & pointOnPlane) { intercept=-normal.DotProduct(pointOnPlane); }

int
PLANE::ClassifyPoint(const VECTOR3D & point) const
{
float distance=point.x*normal.x + point.y*normal.y + point.z*normal.z + intercept;

if(distance>EPSILON) //==0.0f is too exact, give a bit of room
return POINT_IN_FRONT_OF_PLANE;

if(distance<-EPSILON)
return POINT_BEHIND_PLANE;

return POINT_ON_PLANE; //otherwise
}



[edited by - raydog on March 5, 2004 4:58:15 PM]