How do I find slope on a spherical terrain

I have a generated spherical mesh terrain with collider and I need to find if the slope of a triangle at a given point is too steep. I want to only find points with slope close to flat terrain. Basically I need to compare the normal of the triangle to something, however comparing it to Vector3.up doesn’t quite do the trick. And it also returns angles greater than 90, I would expect angles to be only on the range [0, 90]. Don’t need solutions involving raycasting. There must be a way to do it with just vectors.

If you need get a Vector3 on mesh , I dont have idea how do it without raycasting.

But with only one Linecast you can do it.

public LayerMask yourLayer;
    public float distanceToYourFoot; // the distance of your player to you foot (if your player scale is Vector3(x, 2, z) your position is (x, 1, z) distance = 2 (high) - 1 (position) 
    RaycastHit hit;
    float angle;
    private void Update()

        if(Physics.Linecast(transform.position + transform.forward + Vector3.up * 100, transform.position + transform.forward - Vector3.up * 10, out hit, yourLayer))
            Debug.DrawLine(transform.position + transform.forward + Vector3.up * 100, transform.position + transform.forward - Vector3.up * 10,; //Print the line of the LineCast
            Debug.DrawLine(transform.position + Vector3.down * distanceToYourFoot, hit.point,; // Print a Line starting on your position,  to direction you are loocking arround the terrain.

            angle = Vector3.Angle(hit.point - transform.position + Vector3.down * distanceToYourFoot, transform.forward);

            // Value 45 represent just a straight line , the floor is plane, value 90 is a wall 
            // You can get your value based on 0 with 
            // angle -= 45; Now 0 is plane, 45 is a wall


You only need adjust values to your preferences of distances to check and directions.

So if I understand your question correctly you basically have a large sphere mesh with uneven surface which probably resembles a planet like object. What you want to know is the angle between the surface normal of your terrain compared to the normal of the reference sphere at the same point.

The normal of the reference sphere can simply be gathered by taking the worldspace position on the surface of your object and subtract the center of your sphere and normalize the result.

Now you just need to use Vector3.Angle between that reference normal and your surface normal. You can get the surface normal by using a raycast against the MeshCollider of your sphere mesh.

Here’s an image that shows what i mean: