Re: [PlayerStage-Gazebo] Problem with angle meassurement

[Nathan M. <nat...@gm...>]

Hello,

> 1. For X and Y position I have to add 6 to the proxy-X and 4 to the
> proxy-Y - 6 and 4 are the starting coordinates of the robot - Why does
> it not know the correct position? I guess it simulates a odomotry  
> model
> and at the beginning it has not "driven" at all - so it meassures the
> movement - not the position (e.g. the relative position to the  
> starting
> point) - is this correct?
Yes.

> 2. Truth Widget seems somehow instable - at the beinning, the robot
> procy sees no movement at all - which makes sense as I am just  
> standing
> at the start point - and the truth widget suddenly starts turning.  
> This
> happens also in other moments - it's values just change a little all  
> the
> time. Why?
The truth widget is based on the model position in the world. The  
model position is based on ODE. ODE provides unstable motions over a  
long period of time for static motion. To test this, create a world  
with a box, start the simulation, come back twenty minutes later and  
check to see where the box is positioned.

> 3. I read that the angles are meassured in degrees are referencing a
> euler "space". But I can not image that these values are degrees. The
> truth widgets values (3rd column) are way to small and the the proxy
> values (6th column) are bigger but still to small. For the Proxy- 
> Data I
> think it is between -pi and pi. But I am not sure.
> How are the angles meassured for truth widget and PositionProxy2D?
Quaternions and Euler angles, respectively. Note that the TruthWidget  
is providing a 4x1 array for rotation. Generally the conversion is  
done by the underlying code in Gazebo, but if you are interacting  
directly with the TruthWidget, you will need to do the conversion  
(which is a utility function in the library or discussed here: http://en.wikipedia.org/wiki/Conversion_between_quaternions_and_Euler_angles)

Nate