Introduction to pointing

Contact: Alex Drlica-Wagner


The pointing command is a python command-line utility for displaying the pointing history of DECam exposures. By default, it displays a plot of the DES footprint, overlaying the exposures that have been taken during the currently night. The pointing script can be run either as a single instance or in "refresh" mode where it updates every several seconds (30s). This command can be run from kentools or the shell and pointing --help will give you lots of options. By default the start_obs2 script starts a pointing window with a 30s continuous refresh rate (see here for more details on start_obs2). The pointing script shows the footprint projected on the sky at the current time (as it would look if you were to walk outside the dome). As the night progresses, you should see the footprint move across the sky, the moon rise and set, and the number of exposures pile up (if we are lucky).

Some details on the various components of the figure produced with the default settings are as follows:

  • The DES footprint is outlined in blue. The SN fields are also shown in blue, and are explicitly labeled.
  • Single exposures are displayed as transparent hexagonal markers and for the default figure size should be scaled to the DECam focal plane area (this is not true if you manually resize the figure). The most recent exposure is outlined in black.
  • The moon is shown as a gray circle containing the fractional illumination (as determined by pyephem).
  • The large green circle represents the airmass = 1.4 limit imposed by obstac.
  • The small green circle in the center of the image represents the size of the DECam focal plane at zenith. The size of this circle should scale with figure size (so it will let you know if something is wrong).

Details on the various plotting options can be shown by calling pointing --help. A snapshot of the help output is shown below.

> pointing --version 1.1.0
> pointing --help
usage: [-h] [-a AIRMASS] [-b {u,g,r,i,z,Y,VR,all}] [-c COLOR]
                   [-f {des,none}] [--flavor FLAVOR] [-i INFILE]
                   [--legend LEGEND] [-m MOON] [-n NUMEXP] [-o OUTFILE]
                   [--propid PROPID] [--proj {ortho,moll,mol,ait}]
                   [--refresh [REFRESH]] [--since SINCE] [--utc UTC] [-v]
                   [--version] [-z ZENITH]

Where you at?

positional arguments:
  expnum                exposure number to plot (default: None)

optional arguments:
  -h, --help            show this help message and exit
  -a AIRMASS, --airmass AIRMASS
                        draw airmass limit (default: 1.4)
  -b {u,g,r,i,z,Y,VR,all}, --band {u,g,r,i,z,Y,VR,all}
                        draw exposures in specific band (default: all)
  -c COLOR, --color COLOR
                        color corresponding to filter (default: True)
  -f {des,none}, --footprint {des,none}
                        footprint to draw (default: des)
  --flavor FLAVOR       exposure type [object,zero,dome flat,etc.] (default:
  -i INFILE, --infile INFILE
                        list of exposures to draw (default: None)
  --legend LEGEND       draw figure legend (default: True)
  -m MOON, --moon MOON  draw moon location and phase (default: True)
  -n NUMEXP, --numexp NUMEXP
                        number of most recent exposures to plot (default:
  -o OUTFILE, --outfile OUTFILE
                        output file for saving figure (default: None)
  --propid PROPID       draw exposures from specific propid (default: None)
  --proj {ortho,moll,mol,ait}
                        projection for plot (default: ortho)
  --refresh [REFRESH]   refresh interval for figure (seconds). (default: None)
  --since SINCE         UTC for first exposure (defaults to 12 hours)
                        (default: None)
  --utc UTC             UTC for zenith position (defaults to 'now') (default:
  -v, --verbose         output verbosity (default: False)
  --version             show program's version number and exit
  -z ZENITH, --zenith ZENITH
                        draw zenith position (default: True)