I have two triangles in 3d space which share 1 edge and I would like to determine if the angle between their normal vectors is "uphill" or "downhill". In other words, if you set one flat, would the angle between them be acute (uphill) or obtuse (downhill). Hopefully that makes sense.
So far I have the normal vectors of each triangle and have calculated the angle between the two triangles, however this angle is always >= 90 degrees.
Vector3 v1 = triangle1.Normal; Vector3 v2 = triangle2.Normal; float cosAngle = Vector3.Dot(v1, v2) / (v1.magnitude * v2.magnitude); float degAngle = Mathf.Acos(cosAngle) * Mathf.Rad2Deg;
Is there a trick I am missing that lets me determine which direction this angle is in?