On 18 October 2011 00:59, Tim Jenness <[log in to unmask]> wrote:
>
>
> On Mon, Oct 17, 2011 at 2:31 AM, Jean-Baptiste Marquette <[log in to unmask]>
> wrote:
>>
>> Hi David & Dustin,
>> I come back on this issue concerning astrometric calibration on EROS-2
>> images with distortion.
>> You will find on anonymous ftp.iap.fr, directory
>> pub/from_users/marquett/Astrom an archive containing:
>>
>> the image lm00417tbr8k0657.fits calibrated using Starlink's AUTOASTROM
>> the image lm00417tbr8k0657.new.fits calibrated using default parameters
>> of solve-field from astrometry.net
>> various files yielded by this process
>>
>> The original image was linearly calibrated using Emmanuel Bertin's Scamp.
>> In Gaia-Starlink version 4.4.1 on Mac, it appears that:
>>
>> calibration by AUTOASTROM is in agreement with 2MASS catalog over plot.
>> calibration by solve-field shows an offset compared to 2MASS, more
>> pronounced in RA
>>
>> In ds9 6.1.2 on Mac, both images show an offset, not the same way,
>> compared to 2MASS catalog.
>> My guesses are:
>>
>> The QV keywords from AUTOASTROM are correct in lm00417tbr8k0657.fits.
>> However, they are not properly managed in ds9.
>> The SIP keywords in lm00417tbr8k0657.new.fits are wrong, for unknown
>> reasons. But I noted that the CRPIX values are close to the image center.
>> This seems to me not correct, as the image is part of a CCD mosaic, thus the
>> optical axis is far away from the image.
>>
>> It would be nice to have your opinion on this issue. This is critical to
>> make the choice how to calibrate the 1.55 million EROS-2 images.
>> Thanks for your help and expertise,
>
> I'm going to leave details to David but can you give the ds9 7.0beta a
> try: http://hea-www.harvard.edu/RD/ds9/beta.html
> That will understand the QV keywords.
Actually, I think Bill has not yet deployed a beta with QV support. V
7.0 uses AST for wcs transformations, but it specifically strips out
non-standard keywords such as QV before passing them on to AST. I've
now persuaded Bill to leave them in, but he has not yet produced an
updated beta.
David
> I can't really comment on the astrometry.net SIP solution.
> --
> Tim Jenness
>
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