ImageSolver script 1.7.4 anomaly.

[cfranks]

Hi,

I'm using ImageSolver script 1.74 and the results measured for my manual rotator Position Angle are different to those measured by TheSkyX Image Link.  Using 2 images of the same object, one before and one after Meridian Flip and rounding the angles to the nearest degree:

Before flip, TSX measures 55 degrees (the correct setting), ImageSolver measures 125 degrees (180-55).
After flip, TSX measures 235 degrees, ImageSolver measures 125 degrees (360-235).

Using ImageSolver to update the Fits header gives CROTA1 and CROTA2 as 125 for both images.   I haven't yet found how to get TSX Image Link to write the PA in the Fits header hence the use of the IS Script.

This happens with either the Vizier (download) or PPMX (hard drive) catalogues.

PI 1.8 RC5, Win7 Pro x64, plenty of RAM and HDD space.

The script is a pleasure to use and the rest of the co-ordinates measured are accurate.  Many thanks to Andres Pozo.

Regards,
Charles

[Andres.Pozo]

The values of CDELT1, CDELT2, CROTA1 and CROTA2 are calculated following the formulas in the section 6.2 of http://fits.gsfc.nasa.gov/fits_wcs.html "Representations of celestial coordinates in FITS". I have reviewed the implementation and everything seems ok. Anyway, this tags are deprecated since they are cumbersome to use and are superseded by the much better CDi_j, CRPIXj, CRVALi .

Andrés.

[mschuster]

PinPoint and ImageSolver also usually differ by 180 degreees in PA on my subs. The computed CD*_* values appear to agree (within expected errors) but the displayed PA angles don't. Also sometimes there seems to be a difference in the "mirrored" conventions (i.e, what is the sub's rotation and also has it been mirrored or not). Not a big problem, as it is easy to account for the difference, just FYI.

Mike

[cfranks]

Thanks Andres and Mike.  I notice that the Processing Console does show the 'correct' number so I can use that.  I need the PA as I have to set the rotator to what it was, maybe last year when the image was taken, if I want more subs.
Regards
Charles