Q:

Coordinate system and sprite transformation

I'm using andengine to create a physic simulation via box2d.
The bodies are created through PhysicsFactory using Sprites.
My idea is to procedurally position these sprites, following this pattern:
basically one central sprites which represent my world coordinates center, and a series of cloned sprites that are created by rotating the base sprite around myWorld center (the "X" inside the circle).
I've tried to use opengl way inside andengine (translate, rotate, back-translate) 
super(stamiRadious, 0, image);     //stamiDoadious is te distance from radix (world center) and "petal" attach point
this.setRotationCenter(0, 0);
this.setRotation((float) Math.toDegrees(angleRad));
this.setPosition(this.getX()+radixX, this.getY()+radixY);

but i failed: results are not right (wrong final position, and wrong box2d body property as if the sprite is much larger than the image)
I belive part of the problem relies on my interpretation on setRotation and setRotationCenter, and in general on my understanding of andengine coordinates system + box2d cordinates system.
Any thoughts/links to doc/explanation?

A:

Once you created a Physics representation (Body) of a Sprite, you should be very careful on how you modify the Sprite! Usually you don't modify the Sprite anymore at all, but instead modify the Body, by calling 
someBody.setTransform(); // Note that positions must be divided by PhysicsConstants.PIXEL_TO_METER_RATIO_DEFAULT!

Hope that helped :)

