V.3 Improving antenna pointing: PEEK

When the EVLA on-line system conducts a pointing observation, be it for a long series of such observations after antenna moves or a single observation to be applied to the next target source, the software updates a text file with extension .PNT. These files may be copied from the computers at the VLA and then analyzed to determine increments to the parameters of the pointing model. This analysis was done with a program called peek available from Ken Sowinski’s disk area. That program has been adapted to run as an  task. The method of setting the input parameters was changed to be the familiar  methods, the program was given the option to make -style plots in addition to the gnuplot files, and has the option to suppress some of the output text files.

An example usage would be

Do not include the .PNT extension in ASDMFILE; the task will add it. Adverb APARM is used to set data and output selection parameters. The defaults are to include all dates, to include elevations between 7 and 122 degrees, to include all samples with amplitude > 0.01, to omit samples with wind speed > 5 m/s, to include normalized beamwidths between 0.95 and 1.15, and to write the filtered change file only when the change is > 0.1 arc minutes and > 3 times the uncertainty.

Adverb FPARM is used to determine which parameters the task determines, with the default being the usual set (Tilt, Azzero, Elzero, Colima, and Refrac). FPARM can be, but is normally not, used to attach the tilt to the antenna rather than the pad and to suppress the writing of various output text files. These text files are written to the disk area which is the “root” directory of the ASDMFILE adverb — MYAREA:peek/ in the example above. The output files are named with ASDMFILE and extensions .PTR (large overall summary), .gp (gnuplot plotting instructions), .changes (all of the adjustments found), and .filtchg (those adjustments that are deemed significant). In addition, files are written named antnn.dat that include all relevant parameters for all antennas which have been fit and which are used by gnuplot.

You can use the .gp file by typing gnuplot followed by the name of the .gp file. It will make a file named plot.ps. Adverb DOPLOT may be used to request -style plots with substantially better control, using DPARM, over symbol types, sizes, and colors. In both styles of plotting, six plots appear on each plot page showing measured and residual azimuth and elevation corrections plotted against azimuth, elevation, and relative time. You may plot these on the TV or make plot files, one for each antenna fit. If using the TV, button D tells the task to stop plotting but continue doing all the fits and text file outputs. A new procedure to set colors for LWPLA has been written called OKCOLORS. It sets the colors to useful values for plotting on a white background. Black backgrounds use a lot of printer ink and so are less desirable when printing many plots.