Calculate Vector3 position using and Object position + rotation and an angle

Questions & Answers
1

The title sounds a little moronish, most likely the question will sound the same way. Sorry for that in advance.

Top down 2d view game. I have an Parent object named Ship, and a child object named Motor (at the back of the ship). I also have some child objects named Steer (with a number) and depending on which Steer is active right now, i apply force to the Motor position. Whole thing is moving with Rigidbody2D.AddForceAtPosition. This way i can move forward or backward and rotate Ship at the same time.

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Code looks like this:

Vector3 Steer = Steer0.transform.position;

Vector3 forceDirection = (Motor.transform.position - Steer).normalized;

shipBody.AddForceAtPosition(forceDirection * enginePower, Motor.transform.position);

The problem is, i have to use static Steer objects to get their Vector3 coordinates.

I would like to just calculate where is a Steer suppose to be, without having any real object at that position.

I have a Motor position and Motor rotation, i know the angle Between Motor and Steer (at the second picture). I also know the distance between Motor position and a steer position (lets say it 1, since it does not matter), but i can’t understand how do i get Vector3 Steer position from this?

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I’ve tried to use something like this:

Vector3 CalculateSteerCoordinates(float degrees)
    {
        var radians = degrees * Mathf.Deg2Rad;
        var x = Motor.transform.position.x + Mathf.Cos(radians);
        var y = Motor.transform.position.y + Mathf.Sin(radians);
        Vector3 pos =  new Vector3(x, y, 0);
        return pos;
    }

It works, but it does not consider Motor rotation, only it’s coordinates. As a result, it will give incorrect position as soon as i rotate the ship.

2

You can use what you already have, just transform those coordinates from the motor’s local space to world space;

Vector3 CalculateSteerCoordinates(float degrees, float distance)
{
    float radians = degrees * Mathf.Deg2Rad;
    Vector3 localPos = new Vector3 (Mathf.Cos (radians), Mathf.Sin (radians), 0) * distance;
    return Motor.transform.TransformPoint (localPos);
}