We compute positions of one or more stars on images multiple images sets. The stars must be measured in the same order in each images. The difference between the image sets is that are pointed to different sky positions. I usually give letter names to these positions: A,B,C,....

Step 0 - I place all of the Point-set image lists for a given camra 
         in .//S 
    % pwd
    /home/sco/GC_Plate_Scales/2090814/acm/S
    % ls
    list.acm  list.acm_A  list.acm_B  list.acm_C  list.acm_D


Step 1 - Run ds9_imstats_fitslist in Poit-specific directory:
    % pwd
    /home/sco/GC_Plate_Scales/2090814/acm
    % mkdir acm_A
    % cd acm_A 
    % cp ../S/list.acm_A .
    % ds9_imstats_fitslist list.acm_A  FixedRegions N
     --- View each image as the centroid are measured
     --- Do this for all point sets:  acm_B , acm_C, .... 

Step 2 - Compute the mean image offsets using all stars in each point set 
     % pwd
    /home/sco/GC_Plate_Scales/2090814/acm
     % table_XY_offsets.sh ./acm_A/XYmean ./acm_B/XYmean xmean ymean xme yme N  
    Take the last two output lines and enter them into your offste table file (manually) 

Example: 
# Offset statistics from table_XY_offsets.sh (tab1-tab2)
Mean               =      40.9708
Median             =      40.9708
Standard deviation =       2.1634
Mean error of mean =       2.1634
Number of points   =            2
offset(mean, median m.e., N)
      40.971       40.971        2.163     2
 ./acm_A/XYmean  ./acm_B/XYmean  
The last few lines look like: 

So, I put into my file the line: 
    40.971       40.971        2.163     2    ./acm_A/XYmean  ./acm_B/XYmean
 

We use positions taken from the PAS image headers via the OBICX,OBICY cards. Only one star per image is used, but we can use the same lists of images as used in the above approach.

Step 0 - Same as above 

Step 1 - Compute the mean image offsets using image lists directly. 
     % pwd
    /home/sco/GC_Plate_Scales/2090814/acm
    % pas_XY_offsets.sh ./S/list.acm_A ./S/list.acm_B  1.0  N 

    Take the last two output lines and enter them into your offste table file (manually) 

Example: 
Mean   Pos1-Pos2 offset iin pixels =      38.7294
Median Pos1-Pos2 offset iin pixels =      37.8386
mean error on mean offset          =       1.6593
Average number of images per point =   8
offset(mean, median m.e., N)
      38.729       37.839        1.659     8
 ./S/list.acm_A   ./S/list.acm_B

So, I put into my file the line: 
      38.729       37.839        1.659     8    ./S/list.acm_A   ./S/list.acm_B
 

Note that in the two examples above I am treating the A,B points for an acm set. The answere agree within the estimated mean errors. I typicall process the camera set spearately, then I combine the data sets to create lines of (acm,gc1,gc2) for each point set pair. This file, whether prepared with method 1 or 2, can then be processed to compute the gc plate scales and estimated errors.

Below are the toolsthat will be incorportaed into a single code.

 


acm_offset == Given the acm offset (and error) in pixels compute the offset and
              error in arcseconds (for feeding to gcps.sh).
Usage: acm_offset 40.9708 2.1634
arg1 - offset in pixels
arg2 - mean error in pixels
arg3 - run in debug (Y/N)

gcps.sh  == compute gc plate scale when you know the acm offset and error in arcseconds
            and the gc offset in pixels
Usage: gcps Y
arg1 - run in debug mode