Steven,

I'm not sure if this is exactly the problem you are observing, but I
have noticed a similar behavior from ARToolkit before. When the camera
is nearly perpendicular to the marker, and the marker is in the center
of the image, there occurs a singularity. Let's say the angle between
the marker normal and the optical axis is 1 degree - ARToolkit will
arbitrary flip between +1 and -1 degrees. If you make the angle
bigger, the orientation of the marker becomes less ambiguous, and the
error diminishes.

Ivan Dryanovski

On Mon, Nov 8, 2010 at 9:00 AM, Herman Bruyninckx
<Herman.Bruyninckx@mech.kuleuven.be> wrote:
> On Mon, 8 Nov 2010, Steven Bellens wrote:
>
>> 2010/11/8 Steven Bellens <steven.bellens@mech.kuleuven.be>:
>>> Hi,
>>>
>>> I'm experimenting a bit with the ar_pose package. I'm using a single
>>> fixed camera to track a moving marker. To verify the estimation
>>> accuracy, I just leave the marker fixed and I've plotted position and
>>> orientation estimates. The position estimates are pretty much
>>> constant, but the orientation estimates are oscilating a lot (see
>>> appendix), and apparently always between two values. Is this because
>>> of the bad capability to estimate that orientation or can this be
>>> caused by the environment conditions (light - set-up - distance to
>>> marker)?
>>
>> For clarity, plotted are the 4 components of a unit quaternion.
>
> So...? What does a jump of "0.1" quaternion units mean? And is this meaning
> the same for each of the four components?
>
> The answer to this last question is probably "no", hence...?
>
> Herman
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