Errors in fiducial orientation with a SRV1 robot camera
Cesar Fernandez from Spain  [2 posts]
11 years
I'm using Roborealm to navigate a SRV1 robot using fiducials, and I'm facing problems with fiducial location (particularly, with the orientation measures).

I wonder whether the problem comes from the "perspective" or "FL" value in the fiducial module. I am using the default value of 256, and my SRV1 camera has the 3.6mm f2.0 lens. The fiducials are detected without problems; size, X translation and Y translation give correct results; but the orientation measures (X rotation and Y rotation) do not seem to work.

Has someone encountered the same problem? Should I try with a different value for the "FL" parameter?
EDV  [328 posts] 11 years
You could also try AVM Navigator in your navigation task:
Anonymous 11 years

I'm not sure if the FL parameter will help. Can you post the images that are reporting the wrong X and Y values so that we can investigate further? Naturally the FL parameter is taken into account when determining the X and Y rotation but in most cameras that approximate value works. Perhaps the lens you are using on the SRV has a bit more distortion than expected. Seeing a couple example images would help to determine this.

Cesar Fernandez from Spain  [2 posts] 11 years
Thank you Steven.

I attach three images: the setup used for the experiment (SRV1 is facing the fiducial with a -45º orientation); the image captured by the SRV1; and the results output by the fiducial module (Y_rotation = 4.57º). The FL parameter has been set to 90.


Anonymous 11 years

The reason for the error is that the camera on the SRV is not calibrated to show straight lines as straight lines. You will need to un-distort the image before measuring the actual angles. This can be done using the Radial distortion module or the fisheye module when the robot is placed in front of a grid like you have on the table. If you face the robot inline with the grid and use the module to align the lines such that they are actually straight in the image the measurements of the fiducial positions will become more accurate.

To read more about this have a look at



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