How to align a hint arrow to point along a path?

Question

I am using CalculatePath and trying to use path.corners in order to give user a hint for path, that where should he lead next. I am using first two instances of Vector3 of path.corners. Lets call those vectors A and B. Let me illustrate this using figure.

Now I want to position my arrow above the midpoint of the line from B to A, and orient it so it's pointing along the direction from B to A.

When I orient the arrow with LookAt(), it doesn't point in the same direction as the path. Here is an image of my arrow prefab, showing how it's oriented:

Answer 1

It looks like your trouble isn't in computing the direction - it's that your arrow asset was imported with an unusual orientation, so when you use methods like LookAt or LookRotation they give you the "right" result for a standard orientation, leaving your arrow visually pointing somewhere else.

You tried to correct for this by adding angular offsets to the rotation, but the transform.rotation property is not measured in angles - it's a Quaternion, and so we need to use Quaternion methods if we want to modify it.

Usually the cleanest fix here is to re-export your asset in the orientation you really want, or parent it to an empty game object and then rotate the child to align properly with the parent - using the new parent as the root of your prefab.

I'll show you how we can correct the orientation in code though:

void TransformArrow(Vector3 start, Vector3 end, float height)
{
    // This is similar to what you already have.
    Vector3 arrowPosition = (start + end)/2f;
    arrowPosition.y = height;
    arrow.transform.position = arrowPosition;

    Vector3 direction = (end - start);

    // If you want to prevent the arrow from tilting up or down on slopes,
    // uncomment this line.
    // direction.y = 0f;

    Quaternion arrowOrientation = Quaternion.LookRotation(direction);

    // Your prefab arrow points along -x ("left"), with +z ("forward") pointing up.
    // We want to rotate this to Unity's standard: +z forward, y+ up.
    // We'll construct the orientation facing "left" with "forward" up, then invert it.

    Quaternion correction = Quaternion.Inverse(
                               Quaternion.LookRotation(Vector3.left, Vector3.forward)
                            );

    // Now we apply our orientation and the correction for the prefab's orientation.
    arrow.transform.rotation = arrowOrientation * correction;
}