[bug #58640] Error in calculation of SIP to TPV coversions

[Raul Infante-Sainz]

Follow-up Comment #13, bug #58640 (project gnuastro):

Thanks a log guys, now it seems to be good. As you can see the agreement
between them are almost perfect! :-)

Using Python:


                      / World Coordinate System (WCS)
WCSAXES =                    2 / Number of coordinate axes
CRPIX1  =        976.816238403 / Pixel coordinate of reference point
CRPIX2  =        440.521743774 / Pixel coordinate of reference point
PC1_1   =    -1.00022174065751 / Coordinate transformation matrix element
PC1_2   =    -0.00319660295795 / Coordinate transformation matrix element
PC2_1   =    -0.00235639222511 / Coordinate transformation matrix element
PC2_2   =     0.99977077772003 / Coordinate transformation matrix element
CDELT1  =  9.34302943928898E-05 / [deg] Coordinate increment at reference
point
CDELT2  =  9.35240534339602E-05 / [deg] Coordinate increment at reference
point
CUNIT1  = 'deg'                / Units of coordinate increment and value
CUNIT2  = 'deg'                / Units of coordinate increment and value
CTYPE1  = 'RA---TPV'           / TAN (gnomonic) projection + distortions
CTYPE2  = 'DEC--TPV'           / TAN (gnomonic) projection + distortions
CRVAL1  =        39.9265010846 / [deg] Coordinate value at reference point
CRVAL2  =       -8.12618217247 / [deg] Coordinate value at reference point
LONPOLE =                180.0 / [deg] Native longitude of celestial pole
LATPOLE =       -8.12618217247 / [deg] Native latitude of celestial pole
RADESYS = 'FK5'                / Equatorial coordinate system
EQUINOX =               2000.0 / [yr] Equinox of equatorial coordinates
PV1_1   =                   1.0 / TPV coefficient: x
PV1_4   =  2.74744439572126E-03 / TPV coefficient: xx
PV1_5   = -2.51914579463917E-03 / TPV coefficient: xy
PV1_6   = -4.48803400336329E-03 / TPV coefficient: yy
PV2_1   =                   1.0 / TPV coefficient: y
PV2_4   = -2.52742435899630E-03 / TPV coefficient: yy
PV2_5   =  1.75088471295910E-02 / TPV coefficient: yx
PV2_6   = -5.71014067284307E-03 / TPV coefficient: xx

                      / Versions and date
DATE    = '2020-04-14T13:33:00' / file creation date (YYYY-MM-DDThh:mm:ss UT)
CFITSIO = '3.47    '           / CFITSIO version.
WCSLIB  = '6.4     '           / WCSLIB version.
GSL     = '2.6     '           / GNU Scientific Library version.
GNUASTRO= '0.11    '           / GNU Astronomy Utilities version.
COMMIT  = 'v0.2-21-g1d5a5fa-dirty' / Git's commit description in running dir.
END



Using Gnuastro:


                      / World Coordinate System (WCS)
WCSAXES =                    2 / Number of coordinate axes
CRPIX1  =         976.81623840 / Pixel coordinate of reference point
CRPIX2  =         440.52174377 / Pixel coordinate of reference point
PC1_1   =    -1.00022174065751 / Coordinate transformation matrix element
PC1_2   =    -0.00319660295795 / Coordinate transformation matrix element
PC2_1   =    -0.00235639222511 / Coordinate transformation matrix element
PC2_2   =     0.99977077772003 / Coordinate transformation matrix element
CDELT1  =  9.34302943928899E-05 / [deg] Coordinate increment at reference
point
CDELT2  =  9.35240534339601E-05 / [deg] Coordinate increment at reference
point
CUNIT1  = 'deg'                / Units of coordinate increment and value
CUNIT2  = 'deg'                / Units of coordinate increment and value
CTYPE1  = 'RA---TPV'           / TAN (gnomonic) projection + distortions
CTYPE2  = 'DEC--TPV'           / TAN (gnomonic) projection + distortions
CRVAL1  =        39.9265010846 / [deg] Coordinate value at reference point
CRVAL2  =        -8.1261821725 / [deg] Coordinate value at reference point
LONPOLE =                180.0 / [deg] Native longitude of celestial pole
LATPOLE =        -8.1261821725 / [deg] Native latitude of celestial pole
RADESYS = 'FK5'                / Equatorial coordinate system
EQUINOX =               2000.0 / [yr] Equinox of equatorial coordinates
PV1_1   =                  1.0 / TPV coefficient: x
PV1_4   =   2.747444395721E-03 / TPV coefficient: xx
PV1_5   =  -2.519145794639E-03 / TPV coefficient: xy
PV1_6   =  -4.488034003363E-03 / TPV coefficient: yy
PV2_1   =                  1.0 / TPV coefficient: y
PV2_4   =  -2.527424358996E-03 / TPV coefficient: yy
PV2_5   =   1.750884712959E-02 / TPV coefficient: yx
PV2_6   =  -5.710140672843E-03 / TPV coefficient: xx

                      / Versions and date
DATE    = '2020-06-23T23:00:35' / file creation date (YYYY-MM-DDThh:mm:ss UT)
CFITSIO = '3.47    '           / CFITSIO version.
WCSLIB  = '5.17    '           / WCSLIB version.
GSL     = '2.4     '           / GNU Scientific Library version.
GNUASTRO= '0.12.10-ebee'       / GNU Astronomy Utilities version.
END


Just curious. I can see that now there are some coefficients that have been
disappeared, any reason for that?

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