Copying WCS Distortions to a new Image
Josh Walawender wrote on Apr 23, 2010
Hi,
I'm trying to set up a process by which I can add accurate WCS to images in an automated way. The images have little or no WCS info embedded in the header to begin with and my first step is to solve using the Astrometry.net software. This inserts basic info using TAN projection with SIP distortions.
CTYPE1 = 'RA---TAN-SIP' / TAN (gnomic) projection + SIP distortions
CTYPE2 = 'DEC--TAN-SIP' / TAN (gnomic) projection + SIP distortions
However the distortions are not accurate for the edges of the field. I have now solved the WCS for one of the images using MSCTPEAK in IRAF and that is very accurate throughout the field.
What I'd really like to do is use the CRPIXn CRVALn and CDn_m values which are in the header from the Astronomy.net software and then copy the rest of the WCS, including relevant distortion info, from my one MSCTPEAK solved image to all other images. That should be good enough that a catalog overlay would be within a few pixels and then MSCCMATCH would be able to refine the solution without having to be run interactively. Which header values would I need to transfer in order to get those distortion coefficients applied to the images that have been rough solved by Astrometry.net?
thanks!
Josh
I'm trying to set up a process by which I can add accurate WCS to images in an automated way. The images have little or no WCS info embedded in the header to begin with and my first step is to solve using the Astrometry.net software. This inserts basic info using TAN projection with SIP distortions.
CTYPE1 = 'RA---TAN-SIP' / TAN (gnomic) projection + SIP distortions
CTYPE2 = 'DEC--TAN-SIP' / TAN (gnomic) projection + SIP distortions
However the distortions are not accurate for the edges of the field. I have now solved the WCS for one of the images using MSCTPEAK in IRAF and that is very accurate throughout the field.
What I'd really like to do is use the CRPIXn CRVALn and CDn_m values which are in the header from the Astronomy.net software and then copy the rest of the WCS, including relevant distortion info, from my one MSCTPEAK solved image to all other images. That should be good enough that a catalog overlay would be within a few pixels and then MSCCMATCH would be able to refine the solution without having to be run interactively. Which header values would I need to transfer in order to get those distortion coefficients applied to the images that have been rough solved by Astrometry.net?
thanks!
Josh
Last post on Apr 23, 2010