AIPS HELP file for STRAN in 31DEC24
As of Sat Apr 20 7:11:42 2024
STRAN: Task compares ST tables and finds image Coordiantes.
INPUTS
INNAME Image name(name).
INCLASS Image name(class).
INSEQ 0.0 9999.0 Image name(seq. #). 0=>high
INDISK Disk drive #. 0=>any
INVERS ST Table of Star Pixels
IN2VERS 0.0 46655.0 ST Table of Star Coordinates
BPARM 1: >0 update image header
2: Max number of triangles
3: Print Level (0 to 2)
4: >0 not use header as fit
CPARM 1: Min triangle size (pixels)
2: Max triangle size (pixels)
3: Min triangle size (arcsec)
4: Max triangle size (arcsec)
5: Star match distance (pix)
6: Min Number Stars in fit
7: Max Triangle match delta
8: Min Triangle side ratio
DPARM 1: Estimated X Pixel scale
2: Scale error (arcs/pix)
3: Estimated X Pixel scale
4: Scale error (arcs/pix)
5: Orientation Angle
6: Angle error (degrees)
7: Image Center Ra
8: Ra error (degrees)
9: Image Center Dec
10: Dec error (degrees)
HELP SECTION
STRAN
Type: Task
Use: STRAN reads in two ST tables and determines the image
scale and orientation. The first ST table must contain
the pixel locations of stars in the image (See STFND).
The second ST table must contain coordinates (RA+DEC) of
stars in the image (Use, for instance, GSCAT and GSTAR to
read the NASA Guide Star cataloge to get a list of star
coordinates). Since the two ST tables will have the
Stars in different orders, STRAN will search for matching
triangles of sources. Once matches are found, a best
match to the star coordinates will be attempted. NOTE!!!
STRAN WILL ONLY WORK IF THE STAR TABLES HAVE ROUGHLY 30 percent
OVERLAP! (IF ONLY 10 STARS IN 1 TABLE ARE ACTUALLY AMOUNG
1000 STARS IN THE SECOND TABLE, STRAN WILL PROBABLY _NOT_
FIND A SOLUTION.)
IT IS CERTAINLY BEST TO FIRST ESTIMATE THE IMAGE COORDS
AND PLOT THE STAR LOCATIONS FIRST TO COMPARE LISTS.
STRAN BECOMES EXTREAMLY SLOW WITH MORE THAN 300 STARS
PER ST TABLE.
THIS IS AN EXTREAMLY EXPERIMENTAL PROGRAM!!!!!!!!!!!!!!!!
Adverbs:
INNAME......Image name (name). Standard defaults.
INCLASS.....Image name (class). Standard defaults.
INSEQ.......Image name (seq. #). 0 => highest.
INDISK......Disk unit #. 0 => any.
OUTVERS.....Version number of ST (star position) file to be
created. 0 => highest+1.
INFILE......Name of file containing star positions; name
should be of the form:
myarea:filename.ext
EXPLAIN SECTION
STRAN: Task to read two ST (star position) tables and find
the image orientation
RELATED PROGRAMS: CNTR, PCNTR, GREYS, PROFL, STARS, STFND, GSTAR
GSCAT, TABED, PRTAB
DOCUMENTOR: Glen Langston
PURPOSE
STRAN - Attempts an "automatic" determinate of the location,
pixel scale, and orientation of an image. Typical use will be
to determine the orientation of an optical image so that it
can be overlayed with a radio image. Finding the image para-
meters is done by providing STRAN with two ST tables, one
containing the list of PIXEL locations of stars in the image
and the second containing the list of COORDINATE locations of
stars in the image. There must be at least 30 percent overlap in the
star lists. (ie 30 percent of the stars in one list must be present
in the other list, and visa-versa.) STRAN WILL NOT WORK IF
THERE IS NOT SUFFICIENT OVERLAP IN THE ST TABLES. STRAN WILL
WORK MUCH BETTER IF THE TWO LISTS CORRESPOND TO THE SAME STARS!
Use of STRAN requires serveral steps, listed below:
1. Determine the image properties as well as posible. Fill
the image header with the best estimates of the location
of a reference pixel, pixel size and image orientation using
the AIPS verb PUTHEAD. The critical KEYWORDS are listed
below:
CRVAL1 X-Location (ie RA in degrees) of the reference
pixel
CRVAL2 Y-Location (ie DEC in degrees)
CRPIX1 X-Location of reference Pixel (origin of pixel
coordinate system
CRPIX2 Y-Location of reference Pixel
CDELT1 X-Size of a Pixel (in degrees)
CDELT2 Y-Size of a Pixel (in degrees)
CROTA1 Orientation angle of image (in degrees)
CROTA2 Orientation angle of image (usually = CROTA1)
2. Find the Guide Star Table containing the region of interest.
There are Millions of stars in the NASA guide star catalog
so every few 10s of square arc minute region will contain
some Guide Stars. Use the Task GSCAT to read the NASA
provided REGIONS.TBL containing the Guide Star table number
corresponding to each region of the sky.
3. Transfer the Guide Star table of interest to the AIPS area
called FITS (renaming the file to upper case letters).
Use IMLOD to read in the Guide Star Table which will be
called an UK (unknown) AIPS table.
4. Use the Task GSTAR to convert the UK table of coordiantes
into an AIPS ST table.
5. Use the Task TABED to remove all stars outside the region
of interest. If many stars remain (more than 100) use
TABED to remove all but the brightest stars.
Below is a PRTAB listing of the table created by GSTAR
RING-PSS-O .MWFLT . 1 Disk= 3 ST Table version 4
Title: AIPS ST star positions table
Created by GSTAR on 30-JUN-1992 11:04:29
Last written by GSTAR on 02-JUL-1992 00:17:35
Ncol 7 Nrow 2080 Sort cols:
Table has 1 keyword-value pairs: TABEPOCH = b1950.0
COL.NO 1 2 3 4 5 6 7
ROW RA---ARC DEC--ARC DELTRA-- DELTDEC- POSANG STAR LABEL
NUMB DEGREES DEGREES DEGREES DEGREES DEGREES INDEX STR
1 2.52512D+2 1.49264D+1 1.674E-3 1.674E-3 1.281E-2 0.0 S1
2 2.52512D+2 1.49264D+1 1.563E-3 1.563E-3 1.314E-2 0.0 S1
3 2.53565D+2 1.48021D+1 2.681E-3 2.681E-3 1.056E-2 0.0 S2
4 2.53565D+2 1.48020D+1 2.958E-3 2.958E-3 1.009E-2 0.0 S2
5 2.52367D+2 1.50045D+1 1.009E-3 1.009E-3 1.523E-2 0.0 S3
6 2.53312D+2 1.49709D+1 9.801E-4 9.801E-4 1.537E-2 0.0 S4
7 2.53399D+2 1.48005D+1 1.121E-3 1.121E-3 1.473E-2 0.0 S5
...
Note that the Epoch of the coordinates of the stars is
recorded with the keyword TABEPOCH, in this case 1950 coords.
Note that the ST table contains several entries for the same star,
which come from different measurements of the star brightness.
The RA and DEC are in degrees, and the size of the star (columns
3 and 4) are the size of the star on the Palomar sky survey.
The original magnitude of the star is recorded in the Position
angle column, but scaled down by 1000. (ie star S5 in row 7
is a 14.7 magnitude star.)
Make a plot the stars on the image, look for matches.
6. Take the input image and convert it with MWFLT (if necessary)
Usually scanners produce values from 0 to 255, but if it is
desired that the empty sky have values near 0, use MWFLT
to median window subtract the sky.
7. Use the task STFND to find bright stars in the image. First
make ST tables with the star coordiantes, so that CNTR can
be used to mark identified Stars. When the identifications
seem good, make an ST table with Pixel Coordinates.
8. Finally, run STRAN to identify stars in the two lists
and determine the image transformation.
COMMENTS
You can view the contents of the ST file with PRTAB.
The Palomar Sky Survey (PSS) scanned with a page scanner is
expected to be a common input in to STRAN. A few notes about
the PSS: The PSS has a angular scale of 67.3 arc seconds per
millimeter. Since Common scanners use dots per inch scales,
this is converted to arc-seconds per pixel below:
DOTS PER INCH ARC-SECONDS PER PIXEL
------------- ---------------------
800 2.14
600 2.85
400 4.27
300 5.7
200 8.5
100 17.1
75 22.8
50 34.2
The Palomar Sky Survey was done in two colors E (Red) and
O (Blue).