AIPS HELP file for XTRAN in 31DEC24
As of Tue Apr 23 18:27:00 2024
XTRAN: Task to create an image with transformed coodinates
INPUTS
INNAME Input image name. blank=>any
INCLASS Input name(class). blank=>any
INSEQ 0.0 9999.0 Input name(seq. #). 0=>any
INDISK Input disk drive #. 0=>any
OUTNAME Output name(name).
blank=>INNAME
OUTCLASS Output name(class).
blank=>INCLASS
OUTSEQ 0.0 9999.0 Output name(seq. #).
0=>lowest unique
OUTDISK Output image disk drive #
0 => highest with space
BLC Bottom left corner of input
TRC Top right corner of input
ORDER 0.0 6.0 Number of parameters to fit.
(Only 3 or 6 allowed)
DOOUTPUT -2.0 2.0 Transform coordinates
(1 => regrid image to new)
(2 => copy image with fit
parameters in header)
INTEXT File with star positions.
HELP SECTION
XTRAN
Type: Task
Use: XTRAN is a generalized coordinate transformer used to find the
relationship between x,y coordinates in the image and RA and Dec
from user supplied standard star postiions (1000 stars maximum).
If DOOUTPUT is FALSE, the transformation will be calculated, but
the image header will not be updated (DOOUTPUT = -2) and no
output image file will be written (DOOUTPUT=-1). If DOOUTPUT=1,
a new image is created with re-gridding as needed using the
transformation coefficients and filling in the appropriate
parameters in the image header. If DOOUTPUT is 2, a new image is
created by copying the old image with new, fitted header
parameters. This is only correct for simple transformations
(ORDER = 3). Note that these two transformations are not
exactly the same since they do not necessarily use the same
refernce pixel.
WARNING: XTRAN does not do a full non-linear geometry in doing
its fits. Therefore, it is limited in its accuracy and should be
used only for small fields and applications not requiring high
astrometric accuracy.
Adverbs:
INNAME......Input name of image(name). blank=>any
INCLASS.....Input name of image(class). blank=>any
INSEQ.......Input name of image(seq. #). 0=>any
INDISK......Disk drive # of image. 0=>any
OUTNAME.....Output name of image(name). blank=>INNAME
OUTCLASS....Output name of image(class). blank=>INCLASS
OUTSEQ......Output name of image(seq. #). 0=>lowest unique
OUTDISK.....Disk drive # of Output image. 0 => highest with space.
BLC.........The bottom left-hand pixel of the input image which
becomes the bottom left corner of the new image. The
value (0,0) means (1,1).
TRC.........The top right-hand pixel of the input image which becomes
the top right corner of the new image. The value (0,0)
means take the top right hand corner of the image.
ORDER.......Type of transformation: 3 is rotation plus x and y pixel
size. ORDER=6 is rotation, x and y pixel size, plus
quadradic stretch.
DOOUTPUT....If = 1, a new image is created with regridding using the
transformed coordinates from the xy-RA,Dec fit.
If = 2, a new image is created by copying the old image
and adjusting the output header parameters. This is only
appropriate for an ORDER=3 fit.
If = -1, compute the fit as +1 but write no output.
If = -2, compute the fit as +2 but write no output.
INTEXT......File name of standard star positions (8 characters). This
file must have the following format:
(a) The first line contains an initial guess of the RA,
DEC of the center of the image (RA-hr, min,sec,
DEC-deg,min,sec) in the format:
18X,F3.0,F3.0,F7.3,F3.0,F3.0,F6.2
(b) The following lines (up to 20) contain Star name, X
position, Y position, RA-hr, RA-min, RA-sec, DEC-deg,
DEC-min, DEC-sec in the format:
A4,F7.2,F7.2,F3.0,F3.0,F7.3,F3.0,F3.0,F6.2
Note that these are fixed-length Fortran formats; the
characters must appear in the columns as specified. See
the example in the EXPLAIN XTRAN section.
EXPLAIN SECTION
XTRAN: Task to create an image with transformed coodinates
RELATED PROGRAMS: REGRD, STRAN
PURPOSE
XTRAN
Type: Task
Use: XTRAN is a generalized coordinate transformer. XTRAN finds a
coordinate relationship between image pixels and coordinates of objects
located at these pixels (i.e., matching star coordinates to their pixel
locations). If DOOUTPUT is FALSE, only the transformation will be
calculated, but NOT applied to the image. If DOOUTPUT is 1 a new image
is created regridding the input image using the transformation
coefficients. If DOOUTPUT=2, the input image is copied and a corrected
header is supplied. This is only correct for simple transformations.
The fit to the coordinate transformation assumes the X and Y axes are
perpendicular, so that the X transformation can be calculated separately
from the Y transformation. The angle of orientation returned from the
fit is the average of the two fits. Note that if all coordinates are in
a line, a fit is not possible. (ie better fits result from stars
distributed over a large area; stars in a long thin region will not
produce a good fit.)
In the 6-parameter case, the X and Y fits are still done individually.
X distortions must be independent of Y distortions, ie an image can be
compressed in one direction and stretched in another.
The Name of the input file must be in the "standard" DIRECTORY:FILE
format and the file name must be in UPPER CASE LETTERS.
Examples:
INTEXT='myarea:MYSTARS.DAT'
where MYAREA is an environment variable set
before starting AIPS:
percentsetenv MYAREA /mnt/username
The Input Star location file must be provided with fixed format.
Example input file is listed below:
23 22 43.64 -12 23 58.0
STR1 155.98 78.75 23 22 42.23 -12 24 21.8
STR2 169.96 64.92 23 22 38.52 -12 23 23.2
STR3 159.19 67.12 23 22 41.36 -12 23 32.9
STR4 145.08 83.27 23 22 45.48 -12 24 37.8
STR5 133.07 82.89 23 22 49.19 -12 24 38.1
STR6 158.00 83.00 23 22 41.67 -12 24 37.7
AB 151.24 73.26 23 22 43.64 -12 23 58.0
Fortran formats, for those of you too young to know such things are:
18X 18 ignored characters (best left blank)
A4 4 characters
F7.2 7 characters, including a decimal point, blank = 0
F3.0 3 characters, if no decimal it is assumed to follow the 3
(those " 23" = "23.")
The simplest thing to do is to copy the format above EXACTLY.
Full lines that function as comments may be added anywhere in the
file. Comment lines must begin with a dollar sign ($).