Sampleplane is a plane in a 3d space that passes through the origin (0, 0, 0). normalvector is a vector that is perpendicular to sampleplane. assign inplane with true if testvector lies in sampleplane. note: if testvector is a vector that lies in sampleplane, then the dot product of testvector and normalvector is 0. ex: if testvector is [2, 0, -1] and normalvector is [ 0, 1, 0 ], then inplane is 1 (true). if testvector is [-1, 0.1, 1] and normalvector is [0, 1, 0], then inplane is 0 (false).