Create Vector from Angle

Question

I have an angle of rotation in radians. Is there an easy way to convert this to a vector, as I have a 2D sprite ship I want to be able to rotate, and move in the direction of the rotation?

Simon

Answer 1

Can you precise what kind of movement you are tolking to? Because "the direction of rotation" has two meaningful values only - clockwise and counter-clockwise, relatively to rotation axis.

Answer 2

Do you mean something like this?

public Vector2(float angle)
{
    X = (float)Math.Sin(angle);
    Y = (float)Math.Cos(angle);
}


??

Answer 3

I will try that. I have a ship which I want to rotate about its axis, and then move it in the direction it is pointing using the rotation angle. So if that code will do it, then I will give it a shot.

Simon

Answer 4

MattDavey wrote:

Do you mean something like this? public Vector2(float angle) {     X = (float)Math.Sin(angle);     Y = (float)Math.Cos(angle); } ??

The idea is correct but you have to switch your trig functions to :

    X = (float)Math.Cos(angle);
    Y = (float)Math.Sin(angle);

and remember the the north direction (meaning up) is 0 radians and west direction (left) is PI / 2.

Answer 5

Hmm i was always under the impression that 0 degrees was down in computer world - in which case my code was correct. I suppose your choice makes more sense but i've just always used 0deg = down.

Answer 6

Just so you know the XNA framework, uses 0 radians as up. For example when drawing a sprite, and you want to rotate it, in the SpriteBatch.Draw method.