The ability to build finding charts of the sky is critically important for a lot of my activities. I have a plethora of scripts that do this, but they have not been documented well in all cases. A lot of these routine work very well, but with a few refinements they can be greatly improved from the user perspective. Here are some general specifications, some of which have been met.
I have a number of scripts and codes that accomplish some of the goals above. However, they are spread around and not documented to the point where I can easliy learn "what does what". Many of these codes have web docs and online help pages, but these are frequently inadequate. For routine in use as of Aug2017, I have compiled some terse descriptions below. In some cases I have run the suggested Usage messages from the current codes (shown in red). I provide links (in blue) to some of the current documenation.
USNO+DSS Codes
usno_look
For a position (RamDec in sexigecimal form) pull a catalog and image of a
patch of sky. Display the image with ds9. The user specifies a size in arcminutes, and
a magnitude limit to be used in gathering targets from the USNO catalog. There is
some ability to change the way sources are overplotted (just text names, fixed circles
with names, circles coed b color to indicate star and non-star, etc....). The user has
the option to (interactively) request a jpeg of the final view.
usno_look 08:13:15.10 +45:59:29.0 5.0 15.0 1 JustText
skygrab
Much like above, but it can also access SDSS and 2MASS catalogs. A simple set
of labeled, cyan circles are overplotted on the DSS image. I use this in some
high level scripts, but almost alwways to get USNO tagrets. As of Sep2017 there is
no online documentation, but the weblink above is pretty useful. It links to a
lot of low-level things for catalog reading and parsing.
skygrab 08:13:15.10 +45:59:29.0 5.0 Y USNO
usno_identify
Used to display any image with WCS and the corresponding DSS view in a 2-panel
ds9 window. Fairly specialized, but one can easily change the size and color of
the labeling (extremely helpful during my period of eye troubles!). In the example
line below I use the "partially wcs-calibrated" image Rsco5706.fits. I gather stars
down to V=17.0 mag, and I use blue name labels plotted with a font size of 16 (big!).
This is a field in NGC6946, i.e. at low galactic latitude, so I gather 1832 star! The
resultant DSS image is hard to see. To get a new view I would have to re-run the script.
It is faster the second time becasue the same DSS image is recognized and not pulled
from the web again, but a fresh USNO catalog is re-constructed.
% usno_identify Rsco5706.fits 17.0 blue 16
**** This actually useful! If the WCS is fairly good, it is easy to WCS-match the
two images and identify stars in the input image using numbers from the DSS
view. The final result is a ds9 regions file for the input image. The name
for this file is always: show.reg
ds9regget.sh
This OTW code reads a ds9 regions file and makes a more readable ASCII output of the region
properties. This works ONLY for region files using Image or Physical coordinates only.
However, after the ds9regget.sh example below, I show some xpa commands that make ake it
a breeze to write such files using regions plotted with Ra,Dec possitions.
% uds9regget.sh txy.reg any any
% uds9regget.sh txy.reg circle red
To get a region file with image coordinates:
% xpaset -p ds9 regions system image
% xpaset -p ds9 regions save Saved_Coordinates.image.reg
search_ds9reg_by_name
This is fairly low level, but generally useful. It takes the output from
abobe (ds9regget) and spits out the line of data for a region with a specific
name. Hence, in usno_identify I use this routine to find the X,Y of a traget
in frame1 with a name, then I find the Ra,DEC of the source with the same name
in frame2.
cdfp_rd_by_name
Sometimes it is more practical to pull the Ra,Dec of a target from the cdfp
file used to build the ds9 region file. This is what I do in usno_identify.
The sources in frame2 (right) are labeled with text names, but these names
follow the cdfp convention and are really just the line number (after the
header) in the cdfp file (which is usno_targs.cdfp in this case). Once the
user identifies the source in frame1 with a cdfp name, then cdfp_rd_by_name
is used to grab the Ra,Dec value of that source.
cdfp2reg.sh
Thisdoes the inverse of above: it takes a catalog (a cdfp file, CDFP = CoorDinates
in Floating Point) and creates ds9 regions file. This code provides the ability
to plot differnet things (line number name, magnitude, etc...) in addition to just
plotting a circle marker. This code is embedded all over the place, so I really
do not want to change the command line, but putting some backdoor capabilities into
cdfp2reg.sh could be very usefl.
cdfp2reg.sh file 5.0 red X_pixel Y_pixel
The fits_review script was developed in Spet2017 to provide a way to survey many images at one and install rough WCS headers when necessary. I wanted to use this to process HET acm image , as well as my PFC images. In the case of the acm images, there are numerous images taken in a night of data that are not to be reduced (blank sky, camera left running, etc....) and the fiducial points for the WCS are always poor. The PFC usually have no WCS information at all beyond a very rough RA,DEC value. The role of fits_review is to fnd usable images and install upgraded WCS headers.
In reviewing the scripts of the last section, it seems that a good place to start in refining the WCS is to have a look at usno_identify. For intsance, this code already makes ds9 region files that I can directly overplot on ANY image with WCS. The thing that woul greatly add to the use of these files would be the following: size the circle markers according to magnitude. If this done, then it should, for instance, be fairly easy to recognize fiducial points in the acm fields. Once the fiducial point is set to a few arcseconds of accuray, then more automated refinements can proceed.