CCMAP: WCS in fits header

Eduardo A. Gonzalez Solares wrote on Mar 09, 2000

Hi all,

I am working on the astrometry of 4K x 2K images and I am using ccxymatch and
ccmap to calculate an astrometric solution for each frame. Since there are
some important field distortions on the edges of the frames I need to apply a
high order general fit with CCMAP in order to get correct astrometry for the
sources at the edges. My problem is that ccmap only puts in the header of the
image the linear term of the fits, this is, the CD matrix. I can use cctran to
transform appropiately from x,y to ra,dec since the output of ccmap is a
database file with the general astrometric solution. My question is if anybody
knows a way to introduce the general astrometric solution in the header of the
fits image, so that IRAF can understand it and I do not need for an aditional
database file.

Thanks a lot,

Eddie.

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Ludovic Murat wrote on Mar 09, 2000

Sorry ,I have no idea how to help you on this one....... 

	-----Original Message-----
	From:	irafnet@noao.edu [SMTP:irafnet@noao.edu]
	Sent:	Thursday, March 09, 2000 2:23 PM
	To:	lmurat@ubisoft.qc.ca
	Subject:	CCMAP: WCS in fits header

	Hi all,

	I am working on the astrometry of 4K x 2K images and I am using
ccxymatch and
	ccmap to calculate an astrometric solution for each frame. Since
there are
	some important field distortions on the edges of the frames I need
to apply a
	high order general fit with CCMAP in order to get correct astrometry
for the
	sources at the edges. My problem is that ccmap only puts in the
header of the
	image the linear term of the fits, this is, the CD matrix. I can use
cctran to
	transform appropiately from x,y to ra,dec since the output of ccmap
is a
	database file with the general astrometric solution. My question is
if anybody
	knows a way to introduce the general astrometric solution in the
header of the
	fits image, so that IRAF can understand it and I do not need for an
aditional
	database file.

	Thanks a lot,

	Eddie.

---

Lindsey Davis wrote on Mar 09, 2000

Hello Eddie,

>I am working on the astrometry of 4K x 2K images and I am using ccxymatch and
>ccmap to calculate an astrometric solution for each frame. Since there are
>some important field distortions on the edges of the frames I need to apply a
>high order general fit with CCMAP in order to get correct astrometry for the
>sources at the edges. My problem is that ccmap only puts in the header of the
>image the linear term of the fits, this is, the CD matrix. I can use cctran to
>transform appropiately from x,y to ra,dec since the output of ccmap is a
>database file with the general astrometric solution. My question is if anybody
>knows a way to introduce the general astrometric solution in the header of the
>fits image, so that IRAF can understand it and I do not need for an aditional
>database file.
>

To record the higher order terms in the image header set the ccmap projection
parameter to "tnx" instead of "tan". Both ccmap and ccsetwcs will then
update the headers with the full solution, i.e. you will see CTYPE1='RA---TNX'
and CTYPE2='DEC--TNX' in the header and there will be terms of the form
lngcor="...." and latcor="..." in the WAT1_# / WAT2_# keywords. BY default
ccmap only records the best fit linear part of the solution because the TAN
projection is a defacto FITS standard that most other software will understand.
IRAF code understands the TNX projection but other software probably won't. 

If you have saved your database file you don't actually have to repeat the
fits. Just change all the references to "tan" to "tnx" in the database
and run ccsetwcs.

I hope this answers your question.


					      Regards,
					      Lindsey Davis

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Last post on Mar 09, 2000