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The problem here is that the first four parameters on the longitude
axis are reserved for the native longitude and latitude of the projection's fiducial point, and for copies of LONPOLE and LATPOLE. See FITS-WCS paper 2, sections 2.5 and 2.6. So your supplied values are being over-written. Also, a TAN projection shouldn't have any genuine projection parameters, so you're into the realm of undocumented features here anyway. David 2008/10/11 Sean Mattingly : Hi everyone, I've been using WCSLIB to convert some pixel coordinates to world coordinates in a photometry calibration program that I'm currently developing, in C. Due to the nature of some constraints, I'm reading in projection parameters from a text file, and then feeding them directly to a wcsprm struct. However, when I set the struct using wcsset, some of the PV values in the struct change in a strange way! I've put on a printout of a projection parameter file that I read in, and the resulting struct from it. What interests me is that, in the PV column, the PV1_1, PV1_2, PV1_3, and PV1_4 values are extremely different than what I initially fed into the struct before setting it. One can easily see this comparing the projection file and printout from wcsprt(). The projection parameters I am using for this are from SCAMP, an astrometric calibration tool used at Terapix on CFHT and other data. What is strange about my parameters that I'm feeding in is that there is no PV1_3 or PV2_3, even though it ranges from PV1,2_0 to PV1,2_10 (see .ascii headers I've attached). Currently I just put it in as zero. Has anyone had an issue like this before? I'm going to start looking through the wcsset code and see if perhaps something is behaving strangely. Thank you so much in advance for any assistance! Sean Mattingly IPAC, Caltech ----------------------------------------Begin Attach. ****ASCII header file. This contains the projection parameters I feed into the wcsprm. ****** HISTORY Astrometric solution by SCAMP version 1.4.6 (2008-09-15) COMMENT (c) Emmanuel BERTIN COMMENT EQUINOX = 2000.0000 / Mean equinox RADECSYS= 'FK4 ' / Astrometric system CTYPE1 = 'RA---TAN' / WCS projection type for this axis CTYPE2 = 'DEC--TAN' / WCS projection type for this axis CUNIT1 = 'deg ' / Axis unit CUNIT2 = 'deg ' / Axis unit CRVAL1 = 2.811714649E+02 / World coordinate on this axis CRVAL2 = 5.230562978E+01 / World coordinate on this axis CRPIX1 = 4.210600000E+03 / Reference pixel on this axis CRPIX2 = 4.042300000E+03 / Reference pixel on this axis CD1_1 = 5.645524433E-05 / Linear projection matrix CD1_2 = -6.875181636E-07 / Linear projection matrix CD2_1 = -8.675544002E-07 / Linear projection matrix CD2_2 = -5.680880690E-05 / Linear projection matrix PV1_0 = 7.185625209E-04 / Projection distortion parameter PV1_1 = 1.009100977E+00 / Projection distortion parameter PV1_2 = 5.012161938E-03 / Projection distortion parameter PV1_4 = 1.447277893E-02 / Projection distortion parameter PV1_5 = 3.736379604E-02 / Projection distortion parameter PV1_6 = -3.298217608E-03 / Projection distortion parameter PV1_7 = -1.013329269E-01 / Projection distortion parameter PV1_8 = 8.673834317E-02 / Projection distortion parameter PV1_9 = -3.865599315E-02 / Projection distortion parameter PV1_10 = -3.429112379E-02 / Projection distortion parameter PV2_0 = -1.384981525E-03 / Projection distortion parameter PV2_1 = 9.898633315E-01 / Projection distortion parameter PV2_2 = -1.619639610E-02 / Projection distortion parameter PV2_4 = 4.868387579E-02 / Projection distortion parameter PV2_5 = -2.870213784E-02 / Projection distortion parameter PV2_6 = -6.204489712E-02 / Projection distortion parameter PV2_7 = -7.859607786E-02 / Projection distortion parameter PV2_8 = 6.539564176E-03 / Projection distortion parameter PV2_9 = -5.253163953E-02 / Projection distortion parameter PV2_10 = -7.477271745E-02 / Projection distortion parameter FGROUPNO= 2 / SCAMP field group label ASTIRMS1= 5.470387003E-05 / Astrom. dispersion RMS (intern., high S/N) ASTIRMS2= 2.770450580E-05 / Astrom. dispersion RMS (intern., high S/N) ASTRRMS1= 2.902002638E-04 / Astrom. dispersion RMS (ref., high S/ N) ASTRRMS2= 4.848293648E-04 / Astrom. dispersion RMS (ref., high S/ N) ASTINST = 1 / SCAMP astrometric instrument label FLXSCALE= 1.124471704E-03 / SCAMP relative flux scale MAGZEROP= 0.0000 / SCAMP zero- point PHOTIRMS= 0.2428 / mag dispersion RMS (internal, high S/ N) PHOTINST= 1 / SCAMP photometric instrument label PHOTLINK= F / True if linked to a photometric field END *************Output from WCSLIBS wcsprt() of the same wcsprm struct.******************* flag: 137 naxis: 2 crpix: 0x5002e0 4210.6 4042.3 pc: 0x5005c0 pc[0][]: 5.6455e-05 -6.8752e-07 pc[1][]: -8.6755e-07 -5.6809e-05 cdelt: 0x5005e0 1 1 crval: 0x5005f0 281.17 52.306 cunit: 0x502e30 "deg" "deg" ctype: 0x502ec0 "RA---TAN" "DEC--TAN" lonpole: 180.000000 latpole: 52.305630 restfrq: 0.000000 restwav: 0.000000 npv: 22 npvmax: 22 pv: 0x180a800 1 0 0.00071856 1 1 0 1 2 90 1 3 180 1 4 52.306 1 5 0.037364 1 6 -0.0032982 1 7 -0.10133 1 8 0.086738 1 9 -0.038656 1 10 -0.034291 2 0 -0.001385 2 1 0.98986 2 2 -0.016196 2 3 0 2 4 0.048684 2 5 -0.028702 2 6 -0.062045 2 7 -0.078596 2 8 0.0065396 2 9 -0.052532 2 10 -0.074773 nps: 0 npsmax: 8 ps: 0x180ac00 altlin: 2 cd: 0x502f50 cd[0][]: 5.6455e-05 -6.8752e-07 cd[1][]: -8.6755e-07 -5.6809e-05 crota: 0x500600 0 0 alt: ' ' colnum: 0 colax: 0x502f70 0 0 wcsname: UNDEFINED cname: 0x502f80 UNDEFINED UNDEFINED crder: 0x503010 UNDEFINED UNDEFINED csyer: 0x503020 UNDEFINED UNDEFINED radesys: UNDEFINED equinox: UNDEFINED specsys: UNDEFINED ssysobs: UNDEFINED velosys: UNDEFINED ssyssrc: UNDEFINED zsource: UNDEFINED obsgeo: UNDEFINED UNDEFINED UNDEFINED dateobs: UNDEFINED dateavg: UNDEFINED mjdobs: UNDEFINED mjdavg: UNDEFINED ntab: 0 tab: 0x0 nwtb: 0 wtb: 0x0 types: 0x509750 2200 2201 lngtyp: "RA" lattyp: "DEC" lng: 0 lat: 1 spec: -1 cubeface: -1 lin: (see below) cel: (see below) spc: (see below) m_flag: 137 m_naxis: 2 m_crpix: 0x5002e0 (= crpix) m_pc: 0x5005c0 (= pc) m_cdelt: 0x5005e0 (= cdelt) m_crval: 0x5005f0 (= crval) m_cunit: 0x502e30 (= cunit) m_ctype: 0x502ec0 (= ctype) m_pv: 0x180a800 (= pv) m_ps: 0x180ac00 (= ps) m_cd: 0x502f50 (= cd) m_crota: 0x500600 (= crota) m_colax: 0x502f70 (= colax) m_cname: 0x502f80 (= cname) m_crder: 0x503010 (= crder) m_csyer: 0x503020 (= csyer) m_tab: 0x0 (= tab) m_wtb: 0x0 (= wtb) lin.* flag: 137 naxis: 2 crpix: 0x5002e0 4210.6 4042.3 pc: 0x5005c0 pc[0][]: 5.6455e-05 -6.8752e-07 pc[1][]: -8.6755e-07 -5.6809e-05 cdelt: 0x5005e0 1 1 unity: 0 piximg[0][]: 5.6455e-05 -6.8752e-07 piximg[1][]: -8.6755e-07 -5.6809e-05 imgpix[0][]: -0.18588 0.23019 imgpix[1][]: -0.13537 0.22707 m_flag: 0 m_naxis: 0 m_crpix: 0x0 m_pc: 0x0 m_cdelt: 0x0 cel.* flag: 137 offset: 0 phi0: 0.000000 theta0: 90.000000 ref: 281.17 52.306 180 52.306 prj: (see below) euler: 281.17 37.694 180 0.79128 0.61145 latpreq: 0 (not required) isolat: 0 prj.* flag: 103 code: "TAN" r0: 57.295780 pv: (not used) phi0: 0.000000 theta0: 90.000000 bounds: 1 name: "gnomonic" category: 1 (zenithal) pvrange: 0 simplezen: 1 equiareal: 0 conformal: 0 global: 0 divergent: 1 x0: 0.000000 y0: 0.000000 w[]: 0 0 0 0 0 0 0 0 0 0 n: 0 prjx2s: 0x38c8a0 prjs2x: 0x38cac0 spc.* flag: 0 type: " " code: " " crval: UNDEFINED restfrq: 0.000000 restwav: 0.000000 pv: (not used) w: 0 0 0 (remainder unused) isGrism: 0 spxX2P: 0x0 spxP2S: 0x0 spxS2P: 0x0 spxP2X: 0x0 _______________________________________________ fitsbits mailing list http://listmgr.cv.nrao.edu/mailman/listinfo/fitsbits |
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