[Issues] Problems with Global Astrometry

[Erik Deul]

Fedor I. Getman wrote:
> Hi John,
> 
> We updated the python source tree with your modifications and repeated 
> GAS, but  unfortunately  it does not work yet.
> In order to figure out what happens, we checked the intermediate results 
> running GAS manually for the same dataset, but only for 1 ccd.
> It worked apparently well up to the creation of ccd1.cat1 from 
> GAS*.slist.out files.
> 
> Command "asctoldac -i asctoldac.txt -o dither.pairs -c 
> tmp1184771271.14.asctoldac.conf -t PAIRS"
> produced dither.pairs catalog, which can't be read back to ascii format 
> by ldactoasc unless  the "-s" key is used. (Is this normal?)
> 
> Next command "astrom -i ccd1.cat1 -o ccd1.cat2 -p dither.pairs -c 
> tmp1184771271.3.astrom.conf -r dither.residuals"
> gives the completely wrong Ra and Dec positions of objects in 
> dither.residuals catalog with following warnings:
> 
> WARNING(prepare_correl): Serious problem in covariance matrix: Diagonal 
> element 1 is negativeWARNING(prepare_correl): Covariance matrix is non 
> semi-definite positive!! ABS(503586.031250) >1!!! for 0,0
> WARNING(prepare_correl): Covariance matrix is non semi-definite 
> positive!! 1 1 1.000000 0.000000 0.000000
> 
> Finally command "make_distort -i ccd1.cat2 -o ccd1.cat3 -c 
> tmp1184771271.52.make_distort.conf" produces catalog ccd1.cat3 with 
> wrong coordinates of objects.
> 
> So in our case the astrometric solution for each dithering is still wrong.
> 
> We appreciate  a lot your help and any advice you may give us to solve 
> the problem.
> 
> Anna, Mario and Fedor.
> 

Hi Fedor,

Please could you provide me with a copy of the input files so I can have 
a detailed look.

To answer the first question "-s" key: this is perfectly normal as the 
pairs catalog consists out of array elements in table cells only so the 
-s key is required to view the elements of the array.

Erik
> 
> John P. McFarland wrote:
>> Hi Anna and Mario,
>>
>> It appears that my modifications to LDAC's Python wrapper was the cause of 
>> the errors.  The configuration file for asctoldac was being written 
>> incorrectly without any immediate errors.  That problem is now fixed and all 
>> appears well after running the example commands Mario provided below. 
>> Please test things on your side to make sure everything is working correctly 
>> and the results are within the appropriate limits.
>>
>> Cheers,
>>
>>
>> -=John
>>   
> 
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-- 

      _/_/_/_/         _/_/_/                Erik Deul
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