Why do you need the orientation? (assuming you mean the direction of the robot.). If the object you are chasing is in the field of view of the robots camera(s) you should be able to adjust the speed of your wheels to try to center the view of the blob you are chasing. You just need to figure out how much you need the robot to shift its direction to center the blob in its vision, and naturally this is dependent on how far to the sides the blob is.
If you really need the orientation (360 degrees rotational position) then you could do this by having encoders on your wheels to estimate how the direction based on how much rotation it has done. Naturally this will be inaccurate over time since the robot might slip sometimes on its wheels. You could then use a compass sensor, although these can also be inaccurate since they are very sensitive to magnetic fields. Finally you could try to use well known markers in the room where the robot is moving, and calculate its position (and rotation) based on the distance between the markers. Some systems use infrared markers, but these can be expensive.
Finally, you could try a wall detector and get some estimate to its rotation based on this, although you would also need to know how far away from the wall the robot is also. Perhaps vanishing point module could also help here since the point would be fairly centered if the robot was parallell to the walls or features forming the data for the vanishing point calculation. The points offset would then give some data to estimate angular offset from this.
A good system might use several methods and correlate the results to form a more solid position and rotation.
But for chasing a well defined blob (specific color or shape), you dont really need to know the direction... its simple "monkey see, monkey do..." approach. :)
Best,
John
http://robot.lonningdal.net
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