TIME_REQUIREMENTS · BUGS · SEE_ALSO

## NAME

imcctran -- convert between image celestial coordinate systems

## USAGE

`imcctran image outsystem`

## PARAMETERS

- image
- The list of images whose celestial coordinate systems are to be converted. The image celestial coordinate system must be one of the standard FITS celestial coordinate systems: equatorial (FK4, FK4-NO-E, FK5, ICRS, or GAPPT), ecliptic, galactic, or supergalactic.

- outsystem
- The input and output celestial coordinate systems. The options are
the following:
- <imagename> [wcs]
- The celestial coordinate system is the world coordinate system of the image <imagename> and the input or output pixel coordinates may be in the "logical", "tv", "physical" or "world" coordinate systems. If wcs is not specified "logical" is assumed, unless the input coordinates are read from the image cursor, in which case "tv" is assumed. The image celestial coordinate system must be one of the valid FITS celestial coordinate systems: equatorial (FK4, FK4-NO-E, FK5, or GAPPT), ecliptic, galactic, or supergalactic.

- equinox [epoch]
- The equatorial mean place post-IAU 1976 (FK5) system if equinox is a Julian epoch, e.g. J2000.0 or 2000.0, or the equatorial mean place pre-IAU 1976 system (FK4) if equinox is a Besselian epoch, e.g. B1950.0 or 1950.0. Julian equinoxes are prefixed by a J or j, Besselian equinoxes by a B or b. Equinoxes without the J / j or B / b prefix are treated as Besselian epochs if they are < 1984.0, Julian epochs if they are >= 1984.0. Epoch is the epoch of the observation and may be a Julian epoch, a Besselian epoch, or a Julian date. Julian epochs are prefixed by a J or j, Besselian epochs by a B or b. Epochs without the J / j or B / b prefix default to the epoch type of equinox if the epoch value <= 3000.0, otherwise epoch is interpreted as a Julian date. If undefined epoch defaults to equinox.

- icrs [equinox] [epoch]
- The Internaltion Celestial Refernce System where equinox is a Julian or Besselian epoch e.g. J2000.0 or B1980.0. Equinoxes without the J / j or B / b prefix are treated as Julian epochs. The default value of equinox is J2000.0. Epoch is a Besselian epoch, a Julian epoch, or a Julian date. Julian epochs are prefixed by a J or j, Besselian epochs by a B or b. Epochs without the J / j or B / b prefix default to Julian epochs if the epoch value <= 3000.0, otherwise epoch is interpreted as a Julian date. If undefined epoch defaults to equinox.

- fk[equinox] [epoch]
- The equatorial mean place post-IAU 1976 (FK5) system where equinox is a Julian or Besselian epoch e.g. J2000.0 or B1980.0. Equinoxes without the J / j or B / b prefix are treated as Julian epochs. The default value of equinox is J2000.0. Epoch is a Besselian epoch, a Julian epoch, or a Julian date. Julian epochs are prefixed by a J or j, Besselian epochs by a B or b. Epochs without the J / j or B / b prefix default to Julian epochs if the epoch value <= 3000.0, otherwise epoch is interpreted as a Julian date. If undefined epoch defaults to equinox.

- fk[equinox] [epoch]
- The equatorial mean place pre-IAU 1976 (FK4) system where equinox is a Besselian or Julian epoch e.g. B1950.0 or J2000.0, and epoch is the Besselian epoch, the Julian epoch, or the Julian date of the observation. Equinoxes without the J / j or B / b prefix are treated as Besselian epochs. The default value of equinox is B1950.0. Epoch is a Besselian epoch, a Julian epoch, or a Julian date. Julian epochs are prefixed by a J or j, Besselian epochs by a B or b. Epochs without the J / j or B / b prefix default to Besselian epochs if the epoch value <= 3000.0, otherwise epoch is interpreted as a Julian date. If undefined epoch defaults to equinox.

- noefk[equinox] [epoch]
- The equatorial mean place pre-IAU 1976 (FK4) system but without the E-terms where equinox is a Besselian or Julian epoch e.g. B1950.0 or J2000.0, and epoch is the Besselian epoch, the Julian epoch, or the Julian date of the observation. Equinoxes without the J / j or B / b prefix are treated as Besselian epochs. The default value of equinox is B1950.0. Epoch is a Besselian epoch, a Julian epoch, or a Julian date. Julian epochs are prefixed by a J or j, Besselian epochs by a B or b. Epochs without the J / j or B / b prefix default to Besselian epochs if the epoch value <= 3000.0, otherwise epoch is interpreted as a Julian day. If undefined epoch defaults to equinox.

- apparent epoch
- The equatorial geocentric apparent place post-IAU 1976 system where epoch is the epoch of observation. Epoch is a Besselian epoch, a Julian epoch or a Julian date. Julian epochs are prefixed by a J or j, Besselian epochs by a B or b. Epochs without the J / j or B / b prefix default to Besselian epochs if the epoch value < 1984.0, Julian epochs if the epoch value <= 3000.0, otherwise epoch is interpreted as a Julian date.

- ecliptic epoch
- The ecliptic coordinate system where epoch is the epoch of observation. Epoch is a Besselian epoch, a Julian epoch, or a Julian date. Julian epochs are prefixed by a J or j, Besselian epochs by a B or b. Epochs without the J / j or B / b prefix default to Besselian epochs if the epoch values < 1984.0, Julian epochs if the epoch value <= 3000.0, otherwise epoch is interpreted as a Julian day.

- galactic [epoch]
- The IAU 1958 galactic coordinate system. Epoch is a Besselian epoch, a Julian epoch or a Julian date. Julian epochs are prefixed by a J or j, Besselian epochs by a B or b. Epochs without the J / j or B / b prefix default to Besselian epochs if the epoch value < 1984.0, Julian epochs if the epoch value <= 3000.0, otherwise epoch is interpreted as a Julian date. The default value of epoch is B1950.0.

- supergalactic [epoch]
- The deVaucouleurs supergalactic coordinate system. Epoch is a Besselian epoch, a Julian epoch or a Julian date. Julian epochs are prefixed by a J or j, Besselian epochs by a B or b. Epochs without the J / j or B / b prefix default to Besselian epochs if the epoch value < 1984.0, Julian epochs if the epoch value <= 3000.0, otherwise epoch is interpreted as a Julian date. The default value of epoch is B1950.0.

In all the above cases fields in [] are optional with the defaults as described. The epoch field for the fk5, icrs, galactic, and supergalactic coordinate systems is required only if the input coordinates are in the equatorial fk4, noefk4, fk5, or icrs systems and proper motions are defined.

- nx = 10, ny = 10
- The dimensions of the coordinate grid used to compute the rotation angle and, optionally, the x and y magnification factors required to transform the input image celestial coordinate system to the output celestial coordinate system.

- longpole = no
- If longpole = yes the zenithal projections ARC, SIN, STG, TAN, and ZEA will be transformed by updating the longpole and latpole parameters instead of rotating the CD matrix in the usual manner.

- verbose = yes
- Print messages about actions taken by the task on the standard output ?

- update = yes
- Update the image celestial coordinate system ?

## DESCRIPTION

IMCCTRAN converts the celestial coordinate system stored in the headers of the
input images *image*
to the celestial coordinate system specified by
*outsystem*
, and updates the input image header appropriately. The input
and output celestial coordinate systems must be one of the following:
equatorial, ecliptic, galactic, or supergalactic. The equatorial coordinate
systems must be one of: 1) FK4, the mean place pre-IAU 1976 system, 2) FK4-NO-E,
the same as FK4 but without the E-terms, 3) FK5, the mean place post-IAU 1976
system, 4), ICRS, the International Celestial Reference System, 5) GAPPT,
the geocentric apparent place in the post-IAU 1976 system.

The input celestial coordinate system is read from the input image header. IMCCTRAN assumes that the celestial coordinate system is specified by the FITS keywords CTYPE, CRPIX, CRVAL, CD (or alternatively CDELT / CROTA), RADECSYS, EQUINOX (or EPOCH), MJD-WCS (or MJD-OBS, or DATE-OBS). USERS SHOULD TAKE NOTE THAT MJD-WCS IS CURRENTLY NEITHER A STANDARD OR A PROPOSED FITS STANDARD KEYWORD. HOWEVER IT OR SOMETHING SIMILAR, IS REQUIRED TO SPECIFY THE EPOCH OF THE COORDINATE SYSTEM WHICH MAY BE DIFFERENT FROM THE EPOCH OF THE OBSERVATION.

The first four characters of the values of the ra / longitude and dec / latitude axis CTYPE keywords specify the celestial coordinate system. The currently permitted values of CTYPE[1:4] are RA-- / DEC- for equatorial coordinate systems, ELON / ELAT for the ecliptic coordinate system, GLON / GLAT for the galactic coordinate system, and SLON / SLAT for the supergalactic coordinate system.

The second four characters of the values of the ra / longitude and dec / latitude axis CTYPE keywords specify the sky projection geometry. IRAF currently supports the AIT, ARC, CAR, CSC, GLS, MER, PAR, PCO, QSC, SIN, STG, TAN, TSC, and ZEA geometries as well as two internal projection geomemtries TNX, and ZPX. Consequently the currently permitted values of CTYPE[5:8] are -AIT, -ARC, -CAR, -CSC, -GLS, -MER, -PAR, -PCO, -QSC, -SIN, -STG, -TAN, -TSC, -ZEA as well as -ZPX and -TNX.

If the input image celestial coordinate system is equatorial, the value of the RADECSYS keyword specifies which fundamental equatorial system is to be considered. The permitted values of RADECSYS are FK4, FK4-NO-E, FK5, ICRS, and GAPPT. If the RADECSYS keyword is not present in the image header, the values of the EQUINOX / EPOCH keywords (in that order of precedence) are used to determine the fundamental equatorial coordinate system. EQUINOX or EPOCH contain the epoch of the mean place and equinox for the FK4, FK4-NO-E, FK5, and ICRS systems (e.g 1950.0 or 2000.0). The default equatorial system is FK4 if EQUINOX or EPOCH < 1984.0, FK5 if EQUINOX or EPOCH >= 1984.0, and FK5 if RADECSYS, EQUINOX, and EPOCH are undefined. If RADECSYS is defined but EQUINOX and EPOCH are not, the equinox defaults to 1950.0 for the FK4 and FK4-NO-E systems, and 2000.0 for the FK5 and ICRS systems. The equinox value is interpreted as a Besselian epoch for the FK4 and FK4-NO-E systems, and as a Julian epoch for the FK5 and ICRS systems. Users are strongly urged to use the EQUINOX keyword in preference to the EPOCH keyword, if they must enter their own equinox values into the image header. The FK4 and FK4-NO-E systems are not inertial and therefore also require the epoch of the observation (the time when the mean place was correct), in addition to the equinox. The epoch is specified, in order of precedence, by the values of the keywords MJD-WCS or MJD-OBS (which contain the modified Julian date, JD - 2400000.5, of the coordinate system), or the DATE-OBS keyword (which contains the date of the observation in the form DD/MM/YY, CCYY-MM-DD, or CCYY-MM-DDTHH:MM:SS.S). As the latter quantity may only be accurate to a day, the MJD-WCS or MJD-OBS specification is preferred. If all 3 keywords are absent the epoch defaults to the value of equinox. Equatorial coordinates in the GAPPT system require only the specification of the epoch of observation which is supplied via the MJD-WCS, MJD-OBS, or DATE-OBS keywords (in that order of precedence) as for the FK4 and FK4-NO-E system.

If the input image celestial coordinate system is ecliptic the mean ecliptic and equinox of date are required. These are supplied via the MJD-WCS, MJD-OBS, or DATE-OBS keywords (in that order or precedence) as for the equatorial FK4, FK4-NO-E, and GAPPT systems.

The output coordinate system is specified by the *outsystem*
parameter
as described in the PARAMETERS section.

If an error is encountered when decoding the input or output world coordinate
systems, an error message is printed on the standard output (if *verbose*
is "yes"), and the input image left unmodified.

If the input projection is one of the zenithal projections TAN, SIN, STG,
ARC, or ZEA, then the header coordinate tranformation can be preformed by
transforming the CRVAL parameters and rotating the CD matrix as described in
detail below. Otherwise the CRVAL values are transformed, the CD matrix is
left unmodified, and the LONGPOLE and LATPOLE parameters required to perform
the rotation are computed. If *longpole*
is yes then the zenithal
coordinate systems will also be transformed using LONGPOLE and LATPOLE. At
present IRAF looks for longpole and latpole parameters in the approriate
WATN_* keywords. If these are undefined the appropriate default values for
each projection are assumed and new values are written to the WATN_* keywords.

The new image celestial coordinate system is computed as follows. First a
grid of *nx*
by *ny*
pixel and celestial coordinates, evenly spaced
over the input image, is generated using the input image celestial coordinate
system. Next these input celestial coordinates are transformed to coordinates
in the output celestial coordinate system. Next the input celestial coordinates
of the reference point (stored in degrees in the input image CRVAL keywords)
are transformed to coordinates in the output celestial coordinate system,
and new x and y pixel coordinates are computed using the transformed reference
point coordinates but the original input CD matrix. The differences
between the predicted and initial x and y pixel coordinates are used to
compute the x and y axis rotation angles and the x and y magnification factors
required to transform the original CD matrix to the correct new CD matrix.
The process is shown schematically below.

1. x,y(input grid) -> ra,dec(input grid) 2. ra,dec(input grid) -> ra,dec(output grid) 3. ra_ref,dec_ref(input) -> ra_ref,dec_ref(output) 4. ra,dec(output grid) -> x,y(predicted grid) 5. x,y(input grid) -> F -> x,y(predicted grid) 6. cd matrix(input) -> F -> cd matrix(output)

F is the fitted function of the x and y axis rotation angles and the x and y scaling factors required to match the input x and y values to the predicted x and y values.

For most celestial coordinate transformations the fitted x and y scale factors will be very close to 1.0 and the x and y rotation angles will be almost identical. However small deviations from unity scale factors and identical x and y axis rotation angles do occur when transforming coordinates systems with the skewed axes.

The precision of the transformations is usually very high, on the order of 10E-10 to 10E-11 in most cases. However conversions to and from the FK4 equatorial system are less precise as these transformations involve the addition and subtraction of the elliptical aberration or E-terms. In this case the x and y scale factors correct for the first order E-terms and do significantly improve the precision of the coordinate transformation. The quadratic terms, i.e. terms in xy, x**2, and y**2 however are not corrected for, and their absence does diminish the precision of the transformation coordinate transformation. For most practical purposes this loss of precision is insignificant.

After the fit is completed, the celestial coordinates of the reference point in dd:mm:ss.s in the old and new systems, the rotation angle in degrees, the x and y scaling factors, and an estimate of the rms error of the x and y coordinate transformation are printed on the standard output.

If *update*
is yes, then the image header parameters CRVAL, CD,
CTYPE, RADECSYS, EQUINOX, EPOCH, and MJD-WCS are modified, deleted, or
added as appropriate. The position of the reference pixel in the
image (stored in the CRPIX keywords), and the sky projection geometry, e.g.
TAN, SIN, ARC, ETC are unchanged.

USERS NEED TO BE AWARE THAT THE IRAF IMAGE WORLD COORDINATE SYSTEM CURRENTLY (IRAF VERSIONS 2.10.4 PATCH 2 AND EARLIER) SUPPORTS ONLY THE EQUATORIAL SYSTEM (CTYPE (ra axis) = "RA--XXXX" CTYPE (dec axis) = "DEC-XXXX") WHERE XXXX IS THE PROJECTION TYPE, EVEN THOUGH THE IMCCTRAN TASK SUPPORTS GALACTIC, ECLIPTIC, AND SUPERGALACTIC COORDINATES. IMCCTRAN will update the image correctly for non-equatorial systems, but IRAF will not be able to read these transformed image coordinate systems correctly.

USERS SHOULD ALSO REALIZE THAT IMAGE WORLD COORDINATE SYSTEM REPRESENTATION IN FITS IS STILL IN THE DRAFT STAGE. ALTHOUGH IMCCTRAN TRIES TO CONFORM TO THE CURRENT DRAFT PROPOSAL AS MUCH AS POSSIBLE, WHERE NO ADOPTED STANDARDS CURRENTLY EXIST, THE FINAL FITS STANDARD MAY DIFFER FROM THE ONE ADOPTED HERE.

## REFERENCES

Additional information on the IRAF world coordinate systems can be found in the help pages for the WCSEDIT and WCRESET tasks. Detailed documentation for the IRAF world coordinate system interface MWCS can be found in the file "iraf$sys/mwcs/MWCS.hlp". This file can be formatted and printed with the command "help iraf$sys/mwcs/MWCS.hlp fi+ | lprint".

Details of the FITS header world coordinate system interface can be found in the draft paper "World Coordinate Systems Representations Within the FITS Format" by Hanisch and Wells, available from the iraf anonymous ftp archive and the draft paper which supersedes it "Representations of Celestial Coordinates in FITS" by Greisen and Calabretta available from the nrao anonymous ftp archives.

The spherical astronomy routines employed here are derived from the Starlink SLALIB library provided courtesy of Patrick Wallace. These routines are very well documented internally with extensive references provided where appropriate. Interested users are encouraged to examine the routines for this information. Type "help slalib" to get a listing of the SLALIB routines, "help slalib opt=sys" to get a concise summary of the library, and "help <routine>" to get a description of each routine's calling sequence, required input and output, etc. An overview of the library can be found in the paper "SLALIB - A Library of Subprograms", Starlink User Note 67.7 by P.T. Wallace, available from the Starlink archives.

## EXAMPLES

[1]. Precess the equatorial FK5 J2000 celestial coordinate system of the input 512 by 512 pixel square input image to J1975.0.

cl> imcctran image j1975.0 INPUT IMAGE: image Insystem: image logical Projection: TAN Ra/Dec axes: 1/2 Coordinates: equatorial FK5 Equinox: J2000.000 Epoch: J1987.25667351 MJD: 46890.00000 Outsystem: j1975 Coordinates: equatorial FK5 Equinox: J1975.000 Epoch: J1975.00000000 MJD: 42413.25000 Crval1,2: 201:56:43.5, 47:27:16.0 -> 201:40:53.8, 47:35:01.2 dd:mm:ss.s Scaling: Xmag: 1.000000 Ymag: 1.000000 Xrot: 359.923 Yrot: 359.923 degrees Rms: X fit: 8.465123E-11 pixels Y fit: 5.204446E-11 pixels

Before the transformation the image coordinate system looked like the following.

... EPOCH = 2000 DATE-OBS= '05/04/87' CRPIX1 = 257.75 CRPIX2 = 258.93 CRVAL1 = 201.94541667302 CRVAL2 = 47.45444 CDELT1 = -2.1277777E-4 CDELT2 = 2.1277777E-4 CTYPE1 = 'RA---TAN' CTYPE2 = 'DEC--TAN' ...

After the transformation the header looks like the following.

... DATE-OBS= '05/04/87' CRPIX1 = 257.75 CRPIX2 = 258.93 CRVAL1 = 201.681616387759 CRVAL2 = 47.583668865029 CTYPE1 = 'RA---TAN' CTYPE2 = 'DEC--TAN' RADECSYS= 'FK5 ' EQUINOX = 1975. MJD-WCS = 42413.25 WCSDIM = 2 CD1_1 = -2.1277757990523E-4 CD1_2 = 2.84421945372844E-7 CD2_1 = 2.84421945363011E-7 CD2_2 = 2.12777579905235E-4 LTM1_1 = 1. LTM2_2 = 1. WAT0_001= 'system=image' WAT1_001= 'wtype=tan axtype=ra' WAT2_001= 'wtype=tan axtype=dec' ...

Note the the rms of the x and y fits is on the order 10.0e-10 to 10.0e-11 which is the expected numerical precision of the transformation.

[2]. Convert the input image used in example 1 to the BFK4 1950.0 system.

cl> imcctran image B1950.0 INPUT IMAGE: image Insystem: image logical Projection: TAN Ra/Dec axes: 1/2 Coordinates: equatorial FK5 Equinox: J2000.000 Epoch: J1987.25667351 MJD: 46890.00000 Outsystem: B1950 Coordinates: equatorial FK4 Equinox: B1950.000 Epoch: B1950.00000000 MJD: 33281.92346 Crval1,2: 201:56:43.5, 47:27:16.0 -> 201:25:02.3, 47:42:47.1 dd:mm:ss.s Scaling: Xmag: 0.999999 Ymag: 0.999999 Xrot: 359.848 Yrot: 359.848 degrees Rms: X fit: 1.302837E-7 pixels Y fit: 8.545616E-8 pixels

Note that precision of the transformation is still good but is significantly less that the precision of the previous example. This is due to the fact that the quadratic terms in the E-term computation are not included in the transformation.

The transformed image header in this case looks like the following.

... DATE-OBS= '05/04/87' CRPIX1 = 257.75 CRPIX2 = 258.93 CRVAL1 = 201.417300629944 CRVAL2 = 47.7130749603847 CTYPE1 = 'RA---TAN' CTYPE2 = 'DEC--TAN' RADECSYS= 'FK4 ' EQUINOX = 1950. MJD-WCS = 33281.92345905 WCSDIM = 2 CD1_1 = -2.1277680505752E-4 CD1_2 = 5.66226465943254E-7 CD2_1 = 5.66226470798410E-7 CD2_2 = 2.12776805056766E-4 LTM1_1 = 1. LTM2_2 = 1. WAT0_001= 'system=image' WAT1_001= 'wtype=tan axtype=ra' WAT2_001= 'wtype=tan axtype=dec' ...

[3]. Transform the celestial coordinate system of the input image used in examples 1 and 2 to the galactic coordinate system.

cl> imcctran image galactic INPUT IMAGE: image Insystem: image logical Projection: TAN Ra/Dec axes: 1/2 Coordinates: equatorial FK5 Equinox: J2000.000 Epoch: J1987.25667351 MJD: 46890.00000 Outsystem: galactic Coordinates: galactic MJD: 33281.92346 Epoch: J1949.99979044 B1950.00000000 rval1,2: 201:56:43.5, 47:27:16.0 -> 106:01:19.4, 68:27:46.1 dd:mm:ss.s Scaling: Xmag: 1.000000 Ymag: 1.000000 Xrot: 202.510 Yrot: 202.510 degrees Rms: X fit: 9.087450E-11 pixels Y fit: 3.815443E-11 pixels

The transformed header looks like the following.

... DATE-OBS= '05/04/87' CRPIX1 = 257.75 CRPIX2 = 258.93 CRVAL1 = 106.022047915293 CRVAL2 = 68.4627934475432 CTYPE1 = 'GLON-TAN' CTYPE2 = 'GLAT-TAN' MJD-WCS = 33281.92345905 WCSDIM = 2 CD1_1 = 1.96567112095654E-4 CD1_2 = 8.14601120181094E-5 CD2_1 = 8.14601120174619E-5 CD2_2 = -1.9656711209802E-4 LTM1_1 = 1. LTM2_2 = 1. WAT0_001= 'system=image' WAT1_001= 'wtype=tan axtype=glon' WAT2_001= 'wtype=tan axtype=glat' ...

Users should not that although imcctran can write a legal galactic coordinate system to the image header, it and other iraf tasks cannot currently read this coordinate system.

[4]. Repeat the previous example but don't update the image header.

cl> imcctran image galactic update- INPUT IMAGE: image Insystem: image logical Projection: TAN Ra/Dec axes: 1/2 Coordinates: equatorial FK5 Equinox: J2000.000 Epoch: J1987.25667351 MJD: 46890.00000 Outsystem: galactic Coordinates: galactic MJD: 33281.92346 Epoch: J1949.99979044 B1950.00000000 Current wcs Axis 1 2 Crval 201.9454 47.4544 Crpix 257.75 258.93 Cd 1 -2.128E-4 0. Cd 2 0. 2.128E-4 New wcs Axis 1 2 Crval 106.0220 68.4628 Crpix 257.75 258.93 Cd 1 1.966E-4 8.146E-5 Cd 2 8.146E-5 -1.966E-4 Crval1,2: 201:56:43.5, 47:27:16.0 -> 106:01:19.4, 68:27:46.1 dd:mm:ss.s Scaling: Xmag: 1.000000 Ymag: 1.000000 Xrot: 202.510 Yrot: 202.510 degrees Rms: X fit: 9.087450E-11 pixels Y fit: 3.815443E-11 pixels

[5]. Repeat example 1 and check the accuracy of the results by using the skyctran task on the original image and on the transformed image.

cl> type coords 1.0 1.0 512.0 1.0 512.0 512.0 1.0 512.0 cl> skyctran coords STDOUT "image logical" J1975.0 Insystem: image logical Projection: TAN Ra/Dec axes: 1/2 Coordinates: equatorial FK5 Equinox: J2000.000 Epoch: J1987.25667351 MJD: 46890.00000 Outsystem: j1975 Coordinates: equatorial FK5 Equinox: J1975.000 Epoch: J1975.00000000 MJD: 42413.25000 Input file: coords Output file: STDOUT 1.0 1.0 13:27:02.9797 47:31:43.269 512.0 1.0 13:26:24.3330 47:31:43.793 512.0 512.0 13:26:24.3448 47:38:15.219 1.0 512.0 13:27:03.0718 47:38:14.693 cl> imcctran image j1975.0 cl> skyctran coords STDOUT "image logical" "image world" Insystem: image logical Projection: TAN Ra/Dec axes: 1/2 Coordinates: equatorial FK5 Equinox: J1975.000 Epoch: J1975.00000000 MJD: 42413.25000 Outsystem: image world Projection: TAN Ra/Dec axes: 1/2 Coordinates: equatorial FK5 Equinox: J1975.000 Epoch: J1975.00000000 MJD: 42413.25000 Input file: coords Output file: STDOUT 1.0 1.0 13:27:02.9797 47:31:43.269 512.0 1.0 13:26:24.3330 47:31:43.793 512.0 512.0 13:26:24.3448 47:38:15.219 1.0 512.0 13:27:03.0718 47:38:14.693

## TIME REQUIREMENTS

## BUGS

At present IRAF requires that the LONGPOLE and or LATPOLE keywords be defined in the appropriate WAT_* keywords, e.g. WAT1_* and WAT2_* for a 2D image. If these are not present then default values are assumed. The new values are computed and added to the WAT1_* and WAT2_* keywords.

At present the experimental TNX and ZPX projections cannot be transformed with precision. Users should use the SKYCTRAN task to transfrom individual coordinate pairs.

## SEE ALSO

setjd,precess,galactic,xray.xspatial.skypix,stsdas.toolbox.tools.tprecess