[AstroPy] TAN--SIP -> TAN PV WCS projection conversion

[Octavi Fors]

Dear all,

I've been struggling with this for two weeks ago, but no luck so far.

I'm getting the astrometry plate solution of images from a 40ºx40º FoV
camera-lens CCD with Astrometry.net 0.49, TAN--SIP projection, and *5th*
order SIP distortion polynomials.

If I overplot with ds9 the Tycho2 stars in the field in J2000 coordinates
(Analysis->Catalogs->Optical->Tycho2 menu), the green circles match the
positions of all the stars in the FoV.

*However*, after running SExtractor 2.19.5 over the plate solved image,
while the pixel coordinates (XWIN_IMAGE,YWIN_IMAGE) *do* match the stars,
the precessed celestial (ALPHAWIN_J2000,DELTAWIN_J2000) ones *do not* (they
show offsets of several arcmins).

I've asked SExtractor developers if such software does support TAN--SIP WCS
convertion. Still waiting, but my guess is it does not.

So a TAN--SIP->TAN-PV projection converter is what I'm looking for.

Caltech PTF team (see SPIE paper
<http://web.ipac.caltech.edu/staff/shupe/reprints/SIP_to_PV_SPIE2012.pdf>)
made these SIP<->PV converters to 4th order (not to 5th order, which is
what I need). For license issues, they can only release the binaries here
<http://data.astrometry.net/pv2sip-binaries-intel/> , but not the source
code (which would allow me to extend the conversion formulas to 5th order).

Is there anybody in astropy community who is planning to implement a method
in WCS class for converting from SIP to PV projection?
I would be more than happy to provide testing images.

Thanks in advance,

Octavi.

-- 
Octavi Fors
Postdoctoral Research Associate
Department of Physics and Astronomy
The University of North Carolina at Chapel Hill
CB #3255, #157 Phillips Hall
Chapel Hill, NC 27599
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