[Issues] Problems with Global Astrometry

[anna romano]

Hi all,

here in Naples we have problems with Global Astrometry.
For example when we tried to process the Sikkema data, the CCD50 does 
not appear in the final mosaic and the astrometry is wrong in the other 
CCDs.
As an example these are the Astrometric Parameters produced before and 
after Global Astrometry for some exposures/CCDs:

 After AstrometricParametersTask:

Exposure  filter      chip       instr         CD1_1                 
CD1_2               CD2_1               CD2_2         
    1         #878       ccd50     WFI     -6.620125e-05     
3.788299e-07      2.344569e-07      6.592619e-05
    2         #878     ccd50     WFI     -6.628069e-05       1.63594e-07 
     2.694998e-07      6.602958e-05
    1         #878     ccd51    WFI     -6.593424e-05     
-7.156799e-08    -3.319406e-07      6.602225e-05   
    2         #878     ccd51    WFI     -6.628551e-05      
3.087525e-08     6.657912e-08       6.593517e-05   

After GAstromTask:

Exposure  filter      chip       instr         CD1_1                 
CD1_2               CD2_1               CD2_2         
    1         #878    ccd50    WFI     0.001523728     -0.00641293      
0.002444735    -0.01029184   
    2         #878    ccd50    WFI     0.001523728     -0.006415796    
0.002443643    -0.01029184   
    1         #878    ccd51    WFI    -6.596957e-05     
0                       0                        6.598252e-05   
    2         #878    ccd51    WFI    -6.596956e-05     0               
        0                        6.598253e-05

Similar results are systematically produced for other fields: as you 
see, the astrometric parameters are good before gastrom, and completely 
wrong afterwards.
Do you know what could be the reason and do you have any advice?
We also give in attachment an excerpt of the log produced by GAstrom: it 
seems that for some reason it does not find reference/overlapping sources.
Of course, please tell us if we can send you anything else which may be 
useful.

Thanks a lot in advance.

     Anna Romano
    


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