path: root/pkg/images/imcoords/doc/imcctran.hlp

.help imcctran Oct00 images.imcoords
.ih
NAME
imcctran -- convert between image celestial coordinate systems 
.ih
USAGE
imcctran image outsystem
.ih
PARAMETERS
.ls 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.
.le
.ls outsystem
The input and output celestial coordinate systems. The options are
the following:
.ls <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.
.le
.ls 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.
.le
.ls icrs [equinox] [epoch]
The International Celestial Reference 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.
.le
.ls fk5 [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.
.le
.ls fk4 [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.
.le
.ls noefk4 [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.
.le
.ls 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.
.le
.ls 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.
.le
.ls 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.
.le
.ls 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.
.le

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.
.le
.ls 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.
.le
.ls 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.
.le
.ls verbose = yes
Print messages about actions taken by the task on the standard output ?
.le
.ls update = yes
Update the image celestial coordinate system ?
.le

.ih
DESCRIPTION

IMCCTRAN converts the celestial coordinate system stored in the headers of the
input images \fIimage\fR to the celestial coordinate system specified by
\fIoutsystem\fR, 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
geometries 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 \fIoutsystem\fR 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 \fIverbose\fR
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 transformation 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 \fIlongpole\fR 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 appropriate
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 \fInx\fR by \fIny\fR 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.

.nf
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)
.fi

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 \fIupdate\fR 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.

.ih
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.

.ih
EXAMPLES

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

.nf
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
.fi

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

.nf
    ...
    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'
    ...
.fi

After the transformation the header looks like the following.

.nf
    ...
    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'
    ...
.fi

Note 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. 

.nf
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

.fi

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.

.nf
    ...
    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'
    ...
.fi


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

.nf
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
.fi

The transformed header looks like the following.

.nf
    ...
    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'
    ...
.fi

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.

.nf
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
.fi

[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.

.nf
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
.fi

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TIME REQUIREMENTS

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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 transform individual
coordinate pairs.

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