NAME: ABSCAL PURPOSE: Apply the BZERO and BSCALE keyword values in an FITS header to a data array CALLING SEQUENCE: RESULT = ABSCAL( VALUE, HEADER) INPUTS: VALUE - Any scalar, vector, or array (usually an integer type giving a relative intensity). HEADER - A FITS header array containing the absolute calibration keyword BSCALE, and optionally BZERO and BUNIT. OUTPUT: RESULT = BSCALE*VALUE + BZERO, where the BSCALE and BZERO scalars are taken from the FITS header. If the absolute calibration keywords do not exist, then RESULT = VALUE, and !ERR = -1. SYSTEM VARIABLES: If the system variable !DEBUG is set, then ABSCAL will print the calibration units given by the BUNIT keyword. REVISION HISTORY: Written W. Landsman, STX Corporation January 1987
(See /usr/local/idl/lib/zastron/astrom/abscal.pro)
NAME: AD2XY PURPOSE: Compute an X and Y position given the RA and DEC and the astrometry parameters CD, CRPIX, and CRVAL. A tangent (gnomonic) projection is computed directly; other projections are computed using WCSXY2SPH. AD2XY is meant to be used internal to other procedures. For interactive purposes, use ADXY. CALLING SEQUENCE: AD2XY, a ,d, cd, astr, x, y INPUTS: A - R.A. in DEGREES, scalar or vector D - Dec. in DEGREES, scalar or vector ASTR - astrometry structure, output from EXTAST procedure containing: .CD - 2 x 2 array containing the astrometry parameters CD1_1 CD1_2 in DEGREES/PIXEL CD2_1 CD2_2 .CDELT - 2 element vector giving increment at reference point in DEGREES/PIXEL .CRPIX - 2 element vector giving X and Y coordinates of reference pixel (def = NAXIS/2) .CRVAL - 2 element vector giving R.A. and DEC of reference pixel in DEGREES .CTYPE - 2 element vector giving projection types OUTPUTS: X - row position in pixels, scalar or vector Y - column position in pixels, scalar or vector REVISION HISTORY: Converted to IDL by B. Boothman, SASC Tech, 4/21/86 Use astrometry structure, W. Landsman Jan. 1994
(See /usr/local/idl/lib/zastron/astrom/ad2xy.pro)
NAME: ADXY PURPOSE: Use an image header to compute X and Y positions, given the RA and Dec in decimal degrees. CALLING SEQUENCE: ADXY, HDR ;Prompt for Ra and DEC ADXY, hdr, a, d, x, y, [ /PRINT ] INPUTS: HDR - FITS Image header containing astrometry parameters OPTIONAL INPUTS: A - Right ascension in decimal DEGREES, scalar or vector D - Declination in decimal DEGREES, scalar or vector If A and D are not supplied, user will be prompted to supply them in either decimal degrees or HR,MIN,SEC,DEG,MN,SC format. OPTIONAL OUTPUT: X - row position in pixels, same number of elements as A and D Y - column position in pixels OPTIONAL KEYWORD INPUT: PRINT - If this keyword is set and non-zero, then results are displayed at the terminal. OPERATIONAL NOTES: If less than 5 parameters are supplied, or if the /PRINT keyword is set, then then the X and Y positions are displayed at the terminal. If the procedure is to be used repeatedly with the same header, then it would be faster to use AD2XY. REVISION HISTORY: W. Landsman HSTX January, 1988 Use astrometry structure W. Landsman January, 1994
(See /usr/local/idl/lib/zastron/astrom/adxy.pro)
NAME: CONS_DEC PURPOSE: Returns a set of Y pixels values, given an image with tangent projection astrometry, and either (1) A set of X pixel values, and a scalar declination value, or (2) A set of declination values, and a scalar X value Form (1) can be used to find the (X,Y) values of a line of constant declination. Form (2) can be used to find the Y positions of a set declinations, along a line of constant X. CALLING SEQUENCE: Y = CONS_DEC( DEC, X, CD, ASTR, ALPHA) INPUTS: DEC - Declination value(s) in DEGREES (-!PI/2 < DEC < !PI/2). If X is a vector, then DEC must be a scalar. X - Specified X pixel value(s) for line of constant declination If DEC is a vector, then X must be a scalar. ASTR - Astrometry structure, as extracted from a FITS header by the procedure EXTAST OUTPUT: Y - Computed set of Y pixel values. The number of Y values is the same as either DEC or X, whichever is greater. OPTIONAL OUTPUT: ALPHA - the right ascensions (DEGREES) associated with the (X,Y) points RESTRICTIONS: Program will have difficulty converging for declination values near 90. For tangent (gnomonic) projections only. REVISION HISTORY: Written, Wayne Landsman STX Co. April 1988 Algorithm adapted from AIPS memo 27. by Eric Griessen Use new astrometry structure, W. Landsman HSTX Jan. 1994
(See /usr/local/idl/lib/zastron/astrom/cons_dec.pro)
NAME: CONS_RA PURPOSE: Return a set of X pixel values given an image with astrometry, and either (1) a set of Y pixel values, and a scalar right ascension, or (2) a set of right ascension values, and a scalar Y value. In usage (1), CONS_RA can be used to determine the (X,Y) values of a line of constant right ascension. In usage (2), CONS_RA can used to determine the X positions of specified RA values, along a line of constant Y. CALLING SEQUENCE: X = CONS_RA( RA, Y, ASTR) INPUTS: RA - Right Ascension value in DEGREES (0 < RA < 2*PI). If Y is a vector, then RA must be a scalar Y - Specified Y pixel value(s) for line of constant right ascension If RA is a vector, then Y must be a scalar ASTR - Astrometry structure as extracted from a FITS header by the procedure EXTAST OUTPUTS X - Computed set of X pixel values. The number of elements of X is the maximum of the number of elements of RA and Y. RESTRICTIONS: Program will have difficulty converging for declination values near 90. For tangent projection only. REVISION HISTORY: Written, Wayne Landsman STX Co. April, 1988 Algorithm adapted from AIPS memo No. 27 by Eric Griessen New astrometry structure
(See /usr/local/idl/lib/zastron/astrom/cons_ra.pro)
NAME:
EXTAST
PURPOSE:
Extract astrometry parameters from a FITS image header.
The astrometry in the header can be in either CD (Coordinate
description) format, or CROTA and CDELT (AIPS-type) format.
However, the output astrometry will always be in CD format.
CALLING SEQUENCE:
EXTAST, hdr, [ astr, noparams ]
INPUT:
HDR - variable containing the FITS header (string array)
OUTPUTS:
ASTR - Anonymous structure containing astrometry info from the FITS
header. ASTR always contains the following tags (even though
some projections do not require all the parameters)
.CD - 2 x 2 array containing the astrometry parameters CD1_1 CD1_2
in DEGREES/PIXEL CD2_1 CD2_2
.CDELT - 2 element vector giving physical increment at reference pixel
.CRPIX - 2 element vector giving X and Y coordinates of reference pixel
(def = NAXIS/2)
.CRVAL - 2 element double precision vector giving R.A. and DEC of
reference pixel in DEGREES
.CTYPE - 2 element string vector giving projection types, default
['RA---TAN','DEC--TAN']
.LONGPOLE - scalar longitude of north pole (default = 180)
.PROJP1 - Scalar parameter needed in some projections
.PROJP2 - Scalar parameter needed in some projections
NOPARAMS - Scalar indicating the results of EXTAST
-1 = Failure - Header missing astrometry parameters
0 = Success - Header contains CD00n00m + CDELT* astrometry
1 = Success - Header contains CROTA + CDELT (AIPS-type) astrometry
2 = Success - Header contains CDn_m astrometry
PROCEDURE
EXTAST checks for astrometry parameters in the following order:
(1) the CD matrix CD1_1,CD1_2... plus CRPIX and CRVAL.
(2) the CD matrix CD001001,CD001002...plus CRPIX and CRVAL
(3) CROTA2 (or CROTA1) and CDELT plus CRPIX and CRVAL.
See the Memo: Representations of Celestial Coordinates in FITS by
Griesen and Calabretta, available at fits.cv.nrao.edu
NOTES:
(1) An anonymous structure is created to avoid structure definition
conflicts. This is needed because some projection systems
require additional dimensions (i.e. spherical cube
projections require a specification of the cube face).
PROCEDURES CALLED:
ZPARCHECK, SXPAR
REVISION HISTORY
Written by B. Boothman 4/15/86
Accept CD001001 keywords 1-3-88
Accept CD1_1, CD2_1... keywords W. Landsman Nov. 92
(See /usr/local/idl/lib/zastron/astrom/extast.pro)
NAME
FITS_CD_FIX
PURPOSE:
Convert from the representation of the CD matrix in a FITS header
with an underscore (e.g. CDn_m) to that with all integers (e.g.
CD00n00m). According to the proposed World Coordinate System
standard by Griesen and Calabretta, the CD00n00m form is to be
preferred and does not include the plate scale, so that CDELT*
keywords are also needed. The CD1_1 form (used in IRAF) includes
the plate scale (CDELT) factor.
Because of past confusion as to which form to use, it will sometimes
be necessary to convert from one form to the other.
CALLING SEQUENCE:
FITS_CD_FIX, Hdr, [/REVERSE]
INPUT-OUTPUT:
HDR - FITS header, 80 x N string array. If the header does not
contain the CDn_m keywords then it is left unmodified. Other-
wise the CDn_m keywords are removed and the CD00n00m keywords
inserted (with the same values).
OPTIONAL KEYWORD INPUT
REVERSE - If this keyword is set and non-zero, then the process is
reversed, i.e. CD00n00m keywords are removed from the header
and CDn_m keywords are inserted.
REVISION HISTORY:
Written W. Landsman Feb 1990
Major rewrite Feb 1994
(See /usr/local/idl/lib/zastron/astrom/fits_cd_fix.pro)
NAME:
GETROT
PURPOSE:
Derive the counterclockwise rotation angle, and the X and Y scale
factors of an image, from a FITS image header. First parameter
may be either an image header or a CD matrix (in radians).
CALLING SEQUENCE:
GETROT, Hdr, [ Rot, CDelt ]
or
GETROT, Astr, Rot, CDelt
INPUT PARAMETERS:
HDR - FITS Image header (string array). Program will extract the
astrometry structure
or
ASTR - ASTROMETRY structure, of the type returned by BUILDAST or
EXTAST. See BUILDAST.PRO or EXTAST.PRO for details.
OUTPUT PARAMETERS:
ROT - Scalar giving the counterclockwise rotation of NORTH in DEGREES
from the +Y axis of the image.
CDELT- 2 element vector giving the scale factors in DEGREES/PIXEL in
the X and Y directions. Values correspond to the FITS
parameters CDELT1 and CDELT2
SYSTEM VARIABLES:
If the non-standard system variable !DEBUG is set, then procedure
will print the rotation for both the X and Y axis when these values
are unequal. If !DEBUG is set to 2, then the output parameter ROT
will contain both X and Y rotations.
PROCEDURE:
If the FITS header already contains CDELT (and CD or CROTA) keyword,
(as suggested by the proposed Greisen & Calabretta FITS standard)
then this is used for the scale factor.
If the header contains CD keywords but no CDELT keywords, then
REVISION HISTORY:
Written W. Landsman STX January 1987
Convert to IDL V2. M. Greason, STX, May 1990
Option to return both rotations added. J. D. Offenberg, STX, Aug 1991
Accept ASTROMETRY structures as well as CD, HDR. JDO, HSTX, Jan 1993
(See /usr/local/idl/lib/zastron/astrom/getrot.pro)
NAME: GET_EQUINOX PURPOSE: Return the equinox value from a FITS header. Checks for 3 possibilities (1) If the EQUINOX keyword is found and has a numeric value, then this value is returned (2) If the EQUINOX keyword has the values 'J2000' or 'B1950', then either 2000. or 1950. is returned. (3) If the EQUINOX keyword is not found, then GET_EQUINOX will return the EPOCH keyword value. This usage of EPOCH is disparaged. CALLING SEQUENCE: Year = GET_EQUINOX( Hdr, [ Code ] ) INPUTS: Hdr - FITS Header, string array, will be searched for the EQUINOX (or EPOCH) keyword. OUTPUT: Year - Year of equinox in FITS header, numeric scalar OPTIONAL OUTPUT: Code - Result of header search, scalar -1 - EQUINOX or EPOCH keyword not found in header 0 - EQUINOX found as a numeric value 1 - EPOCH keyword used for equinox (not recommended) 2 - EQUINOX found as 'B1950' 3 - EQUINOX found as 'J2000' REVISION HISTORY: Written W. Landsman STX March, 1991
(See /usr/local/idl/lib/zastron/astrom/get_equinox.pro)
NAME:
HASTROM
PURPOSE:
Perform a linear transformation (with POLY_2D) on an image so that
its astrometry is identical with that in a reference header. This
procedure can be used to align two images.
CALLING SEQUENCE:
HASTROM, oldim, oldhd, newim, newhd, refhd, [MISSING = , INTERP = ]
or
HASTROM, oldim, oldhd, refhd, [MISSING = , INTERP =, NGRID = ]
INPUTS:
OLDIM - Image array to be manipulated. If only 3 parameters are
supplied then OLDIM and OLDHD will be modified to contain
the output image array and header
OLDHD - FITS header array for OLDIM, containing astrometry parameters
REFHD - Reference header, containing astrometry parameters. OLDIM
will be rotated, shifted, and compressed or expanded until
its astrometry matches that in REFHD.
OUTPUTS:
NEWIM - Image array after linear tranformation has been performed.
The dimensions of NEWIM will be identical to the NAXIS1 and
NAXIS2 keywords specified in REFHD. Regions on the reference
image that do not exist in OLDIM can be assigned a value with
the MISSING keyword.
NEWHD - Updated FITS image header associated with NEWIM
OPTIONAL INPUT KEYWORDS:
MISSING - Set this keyword to a scalar value which will be assigned
to pixels in the output image which do not correspond to
existing imput images. If not supplied then linear
extrapolation is used. See the IDL manual on POLY_2D.
INTERP - Scalar, one of 0, 1, or 2 determining type of interpolation
0 nearest neighbor, 1 (default) bilinear interpolation,
2 cubic interpolation (only available in V3.5.0 or later)
NGRID - Integer scalar specifying the number of equally spaced grid
points on each axis to use to specify the transformation.
Default is GRID = 3 (9 total grid points). The value of
GRID must always be greater than DEGREE + 1
DEGREE - Integer Scalar specify the degree of the transformation.
See the routine POLYWARP for more info. Default = 1
(linear transformation).
NOTES:
(1) The 3 parameter calling sequence is less demanding on virtual
memory.
(2) The astrometry in OLDHD will be precessed to match the equinox
given in REFHD.
EXAMPLE:
Suppose one has an image array, IM, and an associated FITS header H.
One desires to warp the image array so that it is aligned with another
image with a FITS header, HREF. Both headers contain astrometry info.
Set pixel values to 0 where there is no overlap between the input and
reference image, and use linear interpolation (default)
IDL> hastrom, IM, H, HREF, MISSING = 0
PROCEDURES USED:
zparcheck, check_FITS, sxpar, get_EQUINOX, hprecess, extast,
sxaddpar, sxaddhist, putast
REVISION HISTORY:
Written W. Landsman, STX Co. Feb, 1989
Updated to CHECK_FITS Dec, 1991
New astrometry keywords Mar, 1994
(See /usr/local/idl/lib/zastron/astrom/hastrom.pro)
NAME: HBOXAVE PURPOSE: Box average an image array using the function BOXAVE and update the FITS header array. This procedure is recommended for integer images when photometric precision is desired, because it performs intermediate steps using REAL*4 arithmetic. Otherwise, the procedure HREBIN is much faster. CALLING SEQUENCE: HBOXAVE, Oldim, Oldhd, Newim, Hewhd, box or HBOXAVE, Oldim, Oldhd, box INPUTS: Oldim - the original image array Oldhd - the original image FITS header, string array OPTIONAL INPUTS: box - the box size to be used, integer scalar. If omitted, then HBOXAVE will prompt for this parameter. OPTIONAL OUTPUTS: Newim - the image after boxaveraging Newhd - header for newim containing updated astrometry info If output parameters are not supplied, the program will modify the input parameters OLDIM and OLDHD to contain the new array and updated header. PROCEDURE: The parameters BSCALE, NAXIS1, NAXIS2, CRPIX1, and CRPIX2 and the CD (or CDELT) parameters are updated for the new FITS header. CALLED PROCEDURES: CHECK_FITS - Check that the FITS header is appropriate to the image BOXAVE - Performs box averaging of an image SXPAR, SXADDPAR - Read and write FITS keyword values MODIFICATION HISTORY: Written, Aug. 1986 W. Landsman, STI Corp. IDLV2 changes, sxaddpar format keyword added, J. Isensee, July,1990 Fix 0.5 pixel offset in new CRPIX computation W. Landsman, Dec, 1991
(See /usr/local/idl/lib/zastron/astrom/hboxave.pro)
NAME: HCONGRID PURPOSE: Expand or contract an image using CONGRID and update the associated FITS header array. CALLING SEQUENCE: HCONGRID, oldhd ;Update FITS header only HCONGRID, oldim, oldhd, [ newim, newhd, newx, newy, INTERP=, OUTSIZE =] INPUTS: OLDIM - the original image array OLDHD - the original image FITS header, string array OPTIONAL INPUTS: NEWX - size of the new image in the X direction NEWY - size of the new image in the Y direction The OUTSIZE keyword can be used instead of the NEWX, NEWY parameters OPTIONAL OUTPUTS: NEWIM - the image after expansion or contraction with CONGRID NEWHD - header for newim containing updated astrometry info If output parameters are not supplied, the program will modify the input parameters OLDIM and OLDHD to contain the new array and updated header. OPTIONAL KEYWORD INPUTS: OUTSIZE - Two element integer vector which can be used instead of the NEWX and NEWY parameters to specify the output image dimensions INTERP - 0 for nearest neighbor, 1 for bilinear interpolation 2 for cubic interpolation. Cubic interpolation requires IDL V3.5 or later. PROCEDURE: Expansion or contraction is done using the CONGRID function. neighbor. The parameters BSCALE, NAXIS1, NAXIS2, CRPIX1, and CRPIX2 and the CD (or CDELT) parameters are updated for the new header. NOTES: A FITS header can be supplied as the first parameter without having to supply an image array. The astrometry in the FITS header will be updated to be appropriate to the specified image size. EXAMPLE: Congrid an 512 x 512 image array IM and FITS header H to size 300 x 300 using cubic interpolation IDL> hcongrid, IM ,H, OUT = [300, 300], INTERP = 2 The variables IM and H will be modified to the new image size. MODIFICATION HISTORY: Written, Aug. 1986 W. Landsman, STI Corp. Added interp keywords, J. Isensee, July, 1990 Add cubic interpolation W. Landsman HSTX January 1994
(See /usr/local/idl/lib/zastron/astrom/hcongrid.pro)
NAME: HEXTRACT PURPOSE: Extract a subimage from an array and create a new FITS header with updated astrometry for the subarray CALLING SEQUENCE: HEXTRACT, Oldim, Oldhd, [ Newim, Newhd, x0, x1, y0, y1 ] or HEXTRACT, Oldim, Oldhd, [x0, x1, y0, y1 ] INPUTS: Oldim - the original image array Oldhd - the original image header OPTIONAL INPUTS: x0, x1, y0, y1 - respectively, first and last X pixel, and first and last Y pixel to be extracted from the original image, integer scalars. If omitted, HEXTRACT will prompt for these parameters OPTIONAL OUTPUTS: Newim - the new subarray extracted from the original image Newhd - header for newim containing updated astrometry info If output parameters are not supplied or set equal to -1, then the HEXTRACT will modify the input parameters OLDIM and OLDHD to contain the subarray and updated header. PROCEDURE: The FITS header parameters NAXIS1, NAXIS2, CRPIX1, and CRPIX2 are updated for the extracted image. EXAMPLE: Read an image from a FITS file 'IMAGE', extract a 512 x 512 subimage with the same origin, and write to a new FITS file 'IMAGENEW' IDL> im = READFITS( 'IMAGE', hdr ) ;Read FITS files into IDL arrays IDL> hextract, im, h, 0, 511, 0, 511 ;Extract 512 x 512 subimage IDL> writefits, 'IMAGENEW', im ,h ;Write subimage to a FITS file PROCEDURES CALLED CHECK_FITS, STRN, SXPAR, SXADDPAR, SXADDHIST MODIFICATION HISTORY: Written, Aug. 1986 W. Landsman, STX Corp. Use astrometry structure, W. Landsman Jan, 1994
(See /usr/local/idl/lib/zastron/astrom/hextract.pro)
NAME: HPRECESS PURPOSE: Precess the astrometry in a FITS header to a new equinox CALLING SEQUENCE: HPRECESS, HDR, [ yearf ] INPUT-OUTPUT: HDR - FITS Header, must contain the CRVAL astrometry keywords, and either an EPOCH or EQUINOX keyword. HDR will be modified to contain the precessed astrometry OPTIONAL INPUT: YEARF - Scalar, giving the year of the new (Final) equinox. If not supplied, user will be prompted for this value. METHOD: The CRVAL and CD (or CROTA) keywords are extracted from the header and precessed to the new equinox. The EPOCH or EQUINOX keyword in the header is updated. A HISTORY record is added RESTRICTIONS: The FK4 reference frame is assumed for both equinoxes. PROCEDURES USED: ZPARCHECK, GET_EQUINOX, EXTAST, SXADDPAR, SXADDHIST, PRECESS, PRECESS_CD, PUTAST REVISION HISTORY: Written W. Landsman STX July, 1988 CD matrix precessed - February, 1989 Update EQUINOX keyword when CROTA2 present November, 1992
(See /usr/local/idl/lib/zastron/astrom/hprecess.pro)
NAME: HREBIN PURPOSE: Expand or contract a FITS or SDAS image using REBIN and update the header array. The size of the new image must be an integer factor of the original image size. User can either overwrite the input array, or write to new variables. CALLING SEQUENCE: hrebin, oldhd ;Special calling sequence to just update header hrebin, oldim, oldhd, [ newim, newhd, newx, newy, OUTSIZE = ,SAMPLE = ] INPUTS: OLDIM - the original image array OLDHD - the original image FITS header, string array OPTIONAL INPUTS: NEWX - size of the new image in the X direction, integer scalar NEWY - size of the new image in the Y direction, integer scalar HREBIN will prompt for NEWX and NEWY if not supplied OPTIONAL OUTPUTS: NEWIM - the image after expansion or contraction with REBIN NEWHD - header for newim containing updated astrometry info If output parameters are not supplied, the program will modify the input parameters OLDIM and OLDHD to contain the new array and updated header. OPTIONAL INPUT KEYWORDS: SAMPLE - Expansion or contraction is done using REBIN which uses bilinear interpolation when magnifying and boxaveraging when minifying. If the SAMPLE keyword is supplied and non-zero, then nearest neighbor sampling is used in both cases. OUTSIZE - Two element integer vector which can be used instead of the NEWX and NEWY parameters to specify the output image dimensions PROCEDURE: The parameters BSCALE, NAXIS1, NAXIS2, CRPIX1, and CRPIX2 and the CD (or CDELT) parameters are updated for the new FITS header. EXAMPLE: Compress a 2048 x 2048 image array IM, with header FITS HDR, to a 512 x 512 array. Overwrite the input variables with the compressed image and header. IDL> hrebin, im, hdr, OUT = [512,512] PROCEDURES USED: SXPAR, SXADDHIST, CHECK_FITS MODIFICATION HISTORY: Written, December 1990 W. Landsman, ST System Corp. Update CD1_1 keywords W. Landsman November 1992
(See /usr/local/idl/lib/zastron/astrom/hrebin.pro)
NAME: HREVERSE PURPOSE: Reverse an image about either the X or Y axis, and create a new header with updated astrometry for the reversed image. CALLING SEQUENCE: HREVERSE,oldim,oldhd, [ subs ] ;Update input image and header or HREVERSE, oldim, oldhd, newim, newhd, [ subs ] INPUTS: OLDIM - the original image array OLDHD - the original image header OPTIONAL INPUTS: SUBS - Subs equals 1 to reverse the order of the X dimension, 2 to reverse Y order. If omitted, then HREVERSE will prompt for this scalar parameter. OPTIONAL OUTPUTS: NEWIM - the rotated image, with the same dimensions as Oldim NEWHD - header for newim containing updated astrometry info If output parameters are not supplied, the program will modify the input parameters OLDIM and OLDHD to contain the rotated image and updated header. SIDE EFFECTS: A right-handed coordinate system is converted into a left- handed one, and vice-versa. PROCEDURE: The User's Library procedure REVERSE is used to reverse the image. The CD and CRPIX header parameters are updated for the new header. For AIPS type astrometry, the CDELT parameters are also updated. A history record is also added to the header MODIFICATION HISTORY: Written, Aug. 1986 W. Landsman, STI Corp. Error modifying CROTA angles corrected 9-23-88 Added format keyword, J. Isensee, July, 1990
(See /usr/local/idl/lib/zastron/astrom/hreverse.pro)
NAME: HROT PURPOSE: Rotate an image (cubic, bilinear or nearest neighbor interpolation) and create a new FITS header with updated astrometry for the rotated image. CALLING SEQUENCE: HROT, oldim, oldhd, [ newim, newhd, angle, xc, yc, int, MISSING =, INTERP = ] INPUTS: OLDIM - the original image array OLDHD - the original FITS image header, string array OPTIONAL INPUTS: NEWIM - If NEWIM is set to -1, then the old image and header will be updated ANGLE - Rotation angle degrees counterclockwise XC - X Center of rotation (-1 for center of image) YC - Y Center of rotation (-1 for center of image) INT - 0 for nearest neighbor, 1 for bilinear interpolation 2 for cubic interpolation. Cubic interpolation requires IDL V3.5 or later. OPTIONAL OUTPUTS: NEWIM - the rotated image, with the same dimensions as Oldim NEWHD - header for newim containing updated astrometry info If output parameters are not supplied, the program will modify the input parameters OLDIM and OLDHD to contain the rotated image and updated header. OPTIONAL INPUT KEYWORD: MISSING - Set this keyword to a scalar value which will be assigned to pixels in the output image which do not correspond to existing imput images (e.g if one rotates off-center). If not supplied then linear extrapolation is used. INTERP - scalar set to either 0 (nearest neighbor interpolation), 1 (bilinear interpolation), or 2 (cubic interpolation, V3.5 or later). Either the INTERP keyword or the int parameter can be specified. EXAMPLE: Rotate an image non-interactively 30 degrees counterclockwise. Use bilinear interpolation, and set missing values to 0. IDL> HROT, im_old, h_old, im_new, h_new, 30, -1, -1, 1, MIS = 0 RESTRICTIONS: Unlike the ROT procedure, HROT cannot be used to magnify or or demagnify an image. Use HCONGRID or HREBIN instead. PROCEDURE: The image array is rotated using the ROT procedure. The CD (or CROTA) and CRPIX parameters, if present in the FITS header, are updated for the new rotation. History records are also added to the header PROCEDURES USED: CHECK_FITS, GETOPT, ROT, SXADDPAR, EXTAST, GETROT MODIFICATION HISTORY: Written, Aug. 1986 W. Landsman, ST Systems Corp. Added MISSING keyword, W. Landsman March, 1991 Added cubic interpolation, use astrometry structure Feb 1994
(See /usr/local/idl/lib/zastron/astrom/hrot.pro)
NAME: PUTAST PURPOSE: Put astrometry parameters into a given FITS header. CALLING SEQUENCE: putast, hdr, astr, [EQUINOX =, CD_TYPE = ] or putast, hdr, cd,[ crpix, crval], [ EQUINOX =, CD_TYPE = ] INPUTS: HDR - FITS header, string array. HDR will be updated to contain the supplied astrometry. or CD - 2 x 2 array containing the astrometry parameters CD1_1 CD1_2 CD2_1 CD2_2 in units of DEGREES/PIXEL CRPIX - 2 element vector giving X and Y coord of reference pixel BE SURE THE COORDINATES IN CRPIX ARE GIVEN IN FORTRAN STANDARD (E.G. FIRST PIXEL IN IMAGE IS (1,1) ) CRVAL - 2 element vector giving R.A. and DEC of reference pixel in degrees OUTPUTS: HDR - FITS header now contains the updated astrometry parameters A brief HISTORY record is also added. OPTIONAL KEYWORD INPUTS: EQUINOX - scalar giving equinox (e.g. 1950) of the reference coordinates CD_TYPE - Scalar, either 0, 1 , or 2 specifying how the CD matrix is to be written into the header (0) as CD00n00m values (1) convert to rotation and write as a CROTA2 value (2) as CDn_m value Method 0 is the preferred use suggested in the document "Representations of Celestial Coordinates in FITS" by Griesen and Calabretta. If CD_TYPE is not supplied PUTAST will try to determined the type of astrometry already in the header. If there is no astrometry in the header then the default is CD_TYPE = 0 NOTES: The recommended use of this procedure is to supply an astrometry structure. PROMPTS: If only a header is supplied, the user will be prompted for a plate scale, the X and Y coordinates of a reference pixel, the RA and DEC of the reference pixel, the equinox of the RA and Dec and a rotation angle. PROCEDURES USED: ZPARCHECK, DATATYPE, SXADDPAR, GETOPT REVISION HISTORY Written by W. Landsman 9-3-87 Major rewrite, use new astrometry structure March, 1994
(See /usr/local/idl/lib/zastron/astrom/putast.pro)
NAME:
STARAST
PURPOSE:
Compute an exact astrometry solution using the positions and
coordinates from 2 or 3 reference stars. If 2 stars are used, then
the X and Y plate scales are assumed to be identical, and the
axis are assumed to be orthogonal. Use of three stars will
allow a unique determination of each element of the CD matrix.
CALLING SEQUENCE:
starast, ra, dec, x, y, cd
INPUTS:
RA - 2 or 3 element vector containing the Right Ascension in DEGREES
DEC- 2 or 3 element vector containing the Declination in DEGREES
X - 2 or 3 element vector giving the X position of reference stars
Y - 2 or 3 element vector giving the Y position of reference stars
OUTPUTS:
CD - CD (Coordinate Description) matrix (DEGREES/PIXEL) determined
from stellar positions and coordinates.
EXAMPLE:
To use STARAST to add astrometry to a FITS header H;
IDL> starast,ra,dec,x,y,cd ;Determine CD matrix
IDL> crval = [ra(0),dec(0)] ;Use Star 0 as reference star
IDL> crpix = [x(0),y(0)] +1 ;Include SDAS pixel offset
IDL> putast,H,cd,crpix,crval ;Add parameters to header
METHOD:
The CD parameters are determined by solving the linear set of equations
relating position to local coordinates (l,m)
REVISION HISTORY:
Written, W. Landsman January 1988
(See /usr/local/idl/lib/zastron/astrom/starast.pro)
NAME:
XY2AD
PURPOSE:
Compute R.A. and Dec in radians from X and Y and the plate
solutions in six-parameter format. A tangent (gnomonic) projection is
computed directly; other projections are computed using WCSXY2SPH.
XY2AD is meant to be used internal to other procedures. For interactive
purposes use XYAD.
CALLING SEQUENCE:
XY2AD, x, y, astr, a, d
INPUTS:
X - row position in pixels, scalar or vector
Y - column position in pixels, scalar or vector
ASTR - astrometry structure, output from EXTAST procedure containing:
.CD - 2 x 2 array containing the astrometry parameters CD1_1 CD1_2
in DEGREES/PIXEL CD2_1 CD2_2
.CDELT - 2 element vector giving physical increment at reference pixel
.CRPIX - 2 element vector giving X and Y coordinates of reference pixel
(def = NAXIS/2)
.CRVAL - 2 element vector giving R.A. and DEC of reference pixel
in DEGREES
.CTYPE - 2 element vector giving projection types
.LONGPOLE - scalar longitude of north pole (default = 180)
.PROJP1 - Scalar parameter needed in some projections
.PROJP2 - Scalar parameter needed in some projections
OUTPUT:
A - R.A. in DEGREES, same number of elements as X and Y
D - Dec. in DEGREES, same number of elements as X and Y
RESTRICTIONS:
Note that all angles must be in radians, including CD and CRVAL
Also note that the CRPIX keyword assumes an SDAS-FORTRAN type
array beginning at (1,1), while X and Y give the IDL position
beginning at (0,0).
No parameter checking is performed.
REVISION HISTORY:
Written by R. Cornett, SASC Tech., 4/7/86
Converted to IDL by B. Boothman, SASC Tech., 4/21/86
(See /usr/local/idl/lib/zastron/astrom/xy2ad.pro)
NAME: XYAD PURPOSE: Use astrometry in a FITS image header to compute R.A. and Dec in decimal degrees from X and Y. CALLING SEQUENCE: XYAD, HDR ;Prompt for X and Y positions XYAD, HDR, X, Y, A, D INPUTS: HDR - FITS Image header containing astrometry info OPTIONAL INPUTS: X - row position in pixels, scalar or vector Y - column position in pixels, scalar or vector X and Y should be in IDL convention, (first pixel is (0,0)). OPTIONAL OUTPUT: A - Right ascension in decimal DEGREES, same number of elements as X and Y D - Declination in decimal DEGREES NOTES: If less than 5 parameters are supplied, or /PRINT is set, then then RA and Dec is printed in both decimal and sexigesimal format If this procedure is to be used repeatedly with the same header, then it would be faster to use XY2AD. REVISION HISTORY: W. Landsman STX January,1988
(See /usr/local/idl/lib/zastron/astrom/xyad.pro)
NAME:
XYXY
PURPOSE:
To use a pair of headers to convert X/Y positions from one frame
to another.
CALLING SEQUENCE:
xyxy, hdra, hdrb, xa, ya, [ xb, yb ]
INPUTS:
hdra - The header containing the plate solution describing the
frame of reference being converted FROM.
hdra - The header containing the plate solution describing the
frame of reference being converted TO.
xa - A scalar or vector containing the x coordinate(s) to convert.
ya - A scalar or vector containing the y coordinate(s) to convert.
Must have the same number of elements as 'xa'.
OUTPUTS:
xb - The converted x coordinate(s). If this parameter is not
specified, it is returned through 'xa'.
yb - The converted y coordinate(s). If this parameter is not
specified, it is returned through 'ya'.
PROCEDURE:
The MOUSSE procedures 'xyad' and 'adxy' are used to perform the
conversion. The equinoxes of each header are checked with
"get_equinox" to make sure that they are identical, and "precess"
is used if they are not
MODIFICATION HISTORY:
Written by Michael R. Greason, Hughes-STX, 13 April 1992.
Updated to use ASTROMETRY structures. J.D.Offenberg, HSTX, Jan 1993
(See /usr/local/idl/lib/zastron/astrom/xyxy.pro)