eqn1 = g_x*cos(p)*cos(y) + g_y*(sin(p)*sin(r)*cos(y) - sin(y)*cos(r)) + g_z*(sin(p)*cos(r)*cos(y) + sin(r)*sin(y)) - n_x;
eqn2 = g_x*sin(y)*cos(p) + g_y*(sin(p)*sin(r)*sin(y) + cos(r)*cos(y)) + g_z*(sin(p)*sin(y)*cos(r) - sin(r)*cos(y)) - n_x;
eqn3 = -g_x*sin(p) + g_y*sin(r)*cos(p) + g_z*cos(p)*cos(r) - n_z;