//----------------------------------------------------------------------------// CHECKS IF 2D POINT P IS IN TRIANGLE ABC. RETURNS 1 IF IN, 0 IF OUT//   Given a triangle ABC and a point P, determines if P is inside//   of ABC (regardless of vertex ordering - CCW or CW). 2D version only, but//   this handles the 3D case if appropriately projected to the XY, YZ, or XZ//   planes (by dropping corresponding component; i.e. drop Z in XY projection).//----------------------------------------------------------------------------int Pt2dInTri(Vect2d A, Vect2d B, Vect2d C, Vect2d P){	// FIRST CHECK THE SIGN OF THE Z-COMPONENT OF THE NORMAL BY CALCULATING	// THE CROSS-PRODUCT (ABxBC). THIS WILL DETERMINE THE ORDERING OF THE	// VERTICES. IF NEGATIVE, VERTICES ARE CLOCKWISE ORDER; OTHERWISE CCW.	// THEN EVALUATE SIGN OF Z-COMPONENTS FOR ABxAP, BCxBP, and CAxCP TO	// DETERMINE IF P IS IN "INSIDE" HALF-SPACE FOR EACH EDGE IN TURN ("INSIDE"	// IS DETERMINED BY SIGN OF Z OF NORMAL (VERTEX ORDERING).	// NOTE: FULL CROSS-PRODS ARE NOT REQUIRED; ONLY THE Z-COMPONENTS	Vect2d dAB=B-A, dBC=C-B;  // "REPEATS"	if ((dAB.x*dBC.y-dAB.y*dBC.x) < 0) // CW	{		if (dAB.x*(P.y-A.y) >= dAB.y*(P.x-A.x)) return(0);           // ABxAP		if (dBC.x*(P.y-B.y) >= dBC.y*(P.x-B.x)) return(0);           // BCxBP		if ((A.x-C.x)*(P.y-C.y) >= (A.y-C.y)*(P.x-C.x)) return(0); // CAxCP	}	else // CCW	{		if (dAB.x*(P.y-A.y) < dAB.y*(P.x-A.x)) return(0);           // ABxAP		if (dBC.x*(P.y-B.y) < dBC.y*(P.x-B.x)) return(0);           // BCxBP		if ((A.x-C.x)*(P.y-C.y) < (A.y-C.y)*(P.x-C.x)) return(0); // CAxCP	}	return(1); // "INSIDE" EACH EDGE''S IN-HALF-SPACE (PT P IS INSIDE TRIANGLE)	};//----------------------------------------------------------------------------// CHECKS IF 3D POINT P IS IN 3D TRIANGLE ABC. RETURNS 1 IF IN, 0 IF OUT.// USES 2D VERSION AFTER PROJECTED SINCE THE 3D TRIANGLE IS PROJECTED ON ONE OF // THE PLANES FORMED BY THE PRINCIPAL AXES (XY, YZ, and XZ). N=Normal//---------------------------------------------------------------------------- int Pt3dInTri(Vect3d A, Vect3d B, Vect3d C, Vect3d P, Vect3d N){  // DETERMINE LARGEST COMPONENT OF NORMAL (magnitude, since we want the largest projection)  N.x=ABS(N.x); N.y=ABS(N.y); N.z=ABS(N.z);    // PROJECT ONTO PLANE WHERE LARGEST COMPONENT IS SET TO ZERO  if (N.x>=N.y && N.x>N.z)     // X IS LARGEST SO PROJECT ONTO YZ-PLANE    return( Pt2dInTri(Vect2d(A.y,A.z),Vect2d(B.y,B.z),Vect2d(C.y,C.z),Vect2d(P.y,P.z)) );	else if (N.y>N.x && N.y>N.z) // Y IS LARGEST SO PROJECT ONTO XZ-PLANE    return( Pt2dInTri(Vect2d(A.x,A.z),Vect2d(B.x,B.z),Vect2d(C.x,C.z),Vect2d(P.x,P.z)) );  else                         // Z IS LARGEST SO PROJECT ONTO XY-PLANE    return( Pt2dInTri(Vect2d(A.x,A.y),Vect2d(B.x,B.y),Vect2d(C.x,C.y),Vect2d(P.x,P.y)) );};

quote:Original post by jaba
In Pt3dInTri is not necessary to calculate the distance from point to the plane?

quote:Original post by Yann L

quote:Original post by jaba
In Pt3dInTri is not necessary to calculate the distance from point to the plane?

The distance is assumed to be 0, ie. the point is assumed to lie on the triangle's surface (or very near to it, within some epsilon). If it doesn't, you need to project it along the face normal, onto the surface.