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maths question (Read 403 times)

_lalo_

maths question
Sep 18^th, 2006, 11:10pm

Hi there again!

does anybody know how to calculate the rotation of an object (helicopter) that follows in a certain distance another object (fixed on the mouse) in the way that the nose is always in front (the flight direction)....
I tried something with atan of the distances between both positions but it doesnt exactly the right thing...

I hope finding some mathfreaks here in the artificial live division... ;)

regards, susanne

p.s.:

this is doin something similar - but not really what it should do - it's flash actionscript, but the calculation is the same:

a = (_parent._xmouse-this._x);
b = (_parent._ymouse-this._y);
this._x = _parent._xmouse-0.9*a; //---------movement
this._y = _parent._ymouse-0.9*b; //---------movement
winkel = Math.atan (b/a);
this._rotation = winkel*180/Math.PI;

« Last Edit: Sep 19^th, 2006, 12:17am by _lalo_ »

Daniel Shiffman

Re: maths question
Reply #1 - Sep 19^th, 2006, 12:16am

You are doing this in two dimensions, yes?

It's a little vector math, you can calculate the difference between the two points:

Code:


float dx = x1 - x2;
float dy = y1 - y2;

Then use the atan2 function to return the angle of the vector (dx,dy).

Code:


float angle = (float) Math.atan2(y, x);

Depending on how you are doing your calculation / rotation, you might need to add PI/2 or reverse the polarity of the angle.

Here's more explanation:

http://www.shiffman.net/teaching/the-nature-of-code/vectors/

An example:

This will help too:

http://www.shiffman.net/teaching/the-nature-of-code/steering/

Dan

http://www.learningprocessing.com | http://www.shiffman.net | http://itp.nyu.edu

_lalo_

Re: maths question
Reply #2 - Sep 19^th, 2006, 12:25am

Thanks - two dimensions yes. Hmmm... this is more or less the same that I did - but maybe it's a problem because of +/- as the center(null-point) of the background is not the center of the screen. In Processing I know how to fix that (with pushMatrix) - but in Flash.... I'll keep on working on that and check your teaching-stuff.. greatings from Linz, Susanne

_lalo_

Re: maths question
Reply #3 - Sep 19^th, 2006, 1:20am

Hi Dan

I just made it - too easy always if you got it...
To avoid the flipping of the object I fixed two angles when the rotation is 90 and/or 270 degrees.

but your workshops do look very interesting!

thanks again, Susanne

(hope no-one will block me because of posting actionscript-code ....but I can transfer it into processing code if somebody wants to ;) )

___________________________________________

Code:

a = this._x - that._x;
b = this._y - that._y;
bogen = Math.atan(b/a);
this._rotation = bogen*180/Math.PI;

if (this._x == that._x && this._y <= that._y) {
this._rotation = 270;
}
if (this._x == that._x && this._y >= that._y) {
this._rotation = 90;
}

if (this._x >= that._x) {
this._rotation += 180;
}

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