v10 = x1-x0; v11 = y1-y0; v12 = z1-z0; v20 = x2-x0; v21 = y2-y0; v22 = z2-z0; vx = v11*v22 - v12*v21; vy = v12*v20 - v10*v22; vz = v10*v21 - v11*v20; d = vx*vx + vy*vy + vz*vz; if( d ) d = sqrt( d ); if( d ) { vx /= d; vy /= d; vz /= d; }