nplot, aver_mode, ca, cb, amin, amax, pmin, pmax, npage Plot time-averaged visibility spectra. EXAMPLES -------- 1. Plot vector averaged spectra, autoscaled in amplitude, phase and channels, using the current defaults for what gets plotted. 0>specplot For help move the cursor into the plot window and press 'H'. 0> 2. As in example 1, but use scalar averaging to construct spectra instead of vector averages, and restrict the X-axis range to channels 10 to 20. 0>specplot 0, scalar, 10, 20 For help move the cursor into the plot window and press 'H'. 0> 2. Change all the default parameters that determine what goes into each spectrum and how to plot them, then plot the result. 0>specbase split, kp Specplot will plot baselines of 1:KP 0>specpol I,Q,U,V Specplot polarization selections: I, Q, U, V 0>spectime 355/14:43:29, 356/05, -20 Specplot time range 355/14:43:29 - 356/04:20:30, scan separation=20 mins 0>specsmooth channels, hanning, 3 Specplot smoothing: units=channels window=hanning fwhm=3 0>specopt frequency, "3j+" Specplot x-axis=frequency flags="3+j". 0>specorder polarization, baseline Specplot selection order: polarization baseline 0>specplot 4, vector, 10, 20, 0, 1.3, -180, 180 For help move the cursor into the plot window and press 'H'. 0> ARGUMENTS --------- nplot - Default = 0 (this actually selects 3 plots per page). The number of spectra to plot on each page. Note that 'nplot' spectra are simultaneously constructed in a single pass through the data, so it is faster to plot a few multi-plot pages than to plot a lot of pages of single plots. aver_mode - Default = vector How to time-average visibilities. Valid modes are: vector - Vector average visibilities. scalar - Scalar average visibilities. ca,cb - Default = (All channels observed). The numbers of the first and last channels to be plotted, or 0,0 to select all channels. Channels are numbered contiguously from the first channel of the first observed IF to the last channel of the last observed IF. amin,amax - Default = (Autoscale). The plotted range of amplitudes, or 0,0 to select individually autoscaled amplitude sub-plots. pmin,pmax - Default = -180,180. The plotted range of phases (degrees). npage - Default = 0 When plotting to a non-interactive device and npage is greater than 0, then a maxmimum of npage pages will be plotted. CONTEXT ------- The specplot command plots time-averaged visibility spectra as amplitude and phase versus either spectral-line channel or frequency. The individual spectra of multiple IFs are plotted side by side on the page. Each page is also divided vertically to display multiple spectra, each differing from the last in either the polarization, time range, UV radius range, or the set of baselines averaged. Note that the current stream selection is irrelevant to 'specplot', and the 'select' command need not have been called before invoking 'specplot'. This allows one to decide what channels and polarization to select in advance by looking at visibility spectra with 'specplot'. The averaging mode, 'aver_mode' ------------------------------ Spectra are formed from a weighted average of selected visibilities. Specplot supports two averaging modes: 1. Vector averaging. When visibilities are vector averaged the real and imaginary parts of each visibility are individually averaged and later converted to amplitude and phase for plotting. 2. Scalar averaging. When visibilities are scalar averaged the real and imaginary parts of each visibility are first converted to amplitude and phase. The amplitudes and phases are then individually averaged. The resulting amplitude spectrum is biased updwards by noise but is independant of phase calibration and position shifts. Selecting the number of plots per page. -------------------------------------- To form a spectrum the 'specplot' command has to read raw visibilities from disk and apply accumulated edits, self-calibration corrections, resoff corrections, and position shifts. For large data-sets this is time consuming, so rather than repeat this separately for each spectrum, the 'specplot' command constructs a whole page full of spectra from a single pass through the data. This takes more memory but is potentially much faster when more than one plot is requested per page. The number of plots per page can be specified on the command line and/or interactively. The order in which spectra are plotted. -------------------------------------- The visibilities that are averaged to form each spectrum are selected by U-V radius range, polarization, time and baseline. On a given page only one of these quantities is allowed to change between plotted spectra, but when all values of that quantity have been exhausted, one of the other quantities may be incremented before starting the next page. The order in which the different quantities are incremented is determined by the 'specorder' command. By default, only the baseline selection specified by the 'specbase' command is allowed to increment. This behavior is the equivalent of what one would see after typing: 0>specorder baseline If one wanted the polarization selection to be incremented each time that spectra for all baselines had been plotted, one would type: 0>specorder baseline, polarization The increment order can also be changed incteratively with the 'o' key (see below). See 'help specorder' for the names of each of the selection types. X-axis options -------------- The type of X-axis that is plotted can be changed with the 'specopt' command. By default, amplitude and phase are plotted versus channel number. Spectral resolution ------------------- The resolution of the plotted spectra can be reduced by smoothing them. The specsmooth command specifies the smoothing parameters to be used. The smoothing width may be specified in terms of channels or frequency. Error bars ---------- By default error bars are plotted for each spectral-line channel. They are toggled on or off with the 'e' key. They are formed from the individual visibility weights that go into the weighted average for each channel, which are interpretted as being the reciprocal of the square of the amplitude uncertainty. If this is not true, see the 'wtscale' command. The error bars also take into account any smoothing that has been applied during plotting. This is described in the help pages of the specsmooth command. Plot styles ----------- By default, neighboring channels are plotted joined by lines in a staircase or histogram-like manner. This shows the real channel widths and sampling. Altenatively, lines can be drawn between the centers of neigboring channels. The latter looks aesthetically better when multi-channel smoothing has been selected. A third alternative is to simply plot each spectral-line channel as an isolated point. Points are then plotted at the center of each channel. Interactive options ------------------- At any time while running specplot, a list of the key bindings that specplot understands will be displayed if you hit the 'H' key on your keyboard. The current key bindings include: H - List all key bindings. X - Exit specplot (right-mouse-button). L - Redisplay the current plot. N - Display the next page of spectra. P - Display the preceding page of spectra. s - Change the number of spectra plotted per page. Beware, this requires a new pass through the data and may take some time with a large data-set. S - Change the plotted spectral resolution by setting or de-selecting smoothing parameters. 1 - Plot only amplitudes. 2 - Plot only phases. 3 - Plot both amplitudes and phases. E - Toggle whether error bars are plotted. V - Toggle between vector and scalar averaged spectra. Beware, this requires a new pass through the data and may take some time with a large data-set. t - Change the baselines, polarization or times used to construct spectra. You will be asked to specify a selection type name and zero or more specification arguments. The specification arguments have the same format as the equivalent command-line commands: baseline, group|split, baseline_group1, ... (see help specbase). polarization, polarization_name1, ... (see help specpol). time, start_time, end_time, scan_time (see help spectime). uvrange, uvmin, uvmax, uvstep (see help specuvr). o - Change the order in which selections are incremented. You will be asked for one or more selection names, in the same format as documented for the 'specorder' command. See 'help specorder' for details. u - Delimit a X-axis range with the cursor (hit u twice for full range). Either press this key (u) a second time to undo a previous range selection, or delimit the desired X-axis range by pressing the 'A' key (left mouse button), once at each end of its extent. The range selection can be cancelled while in this mode by pressing the 'D' key (middle mouse button). U - Change the X-axis type. You will be prompted for the name of a recognized axis type. See help specopt for a list of valid type names. Z - Select a new amplitude or phase range (hit Z twice for full range). Either press this key (Z) a second time to undo a previous range selection, or delimit the desired amplitude or phase range by pressing the 'A' key (left mouse button), once at each end of its extent. The range selection can be cancelled while in this mode by pressing the 'D' key (middle mouse button). j - Toggle whether to join points with lines. This toggles whether channel values are plotted as isolated points, or are whether they are joined by lines. If joined points are selected, there format can be further selected with the 'J' key described below. J - Toggle between two possible line styles. By default the lines are drawn as bins, in a staircase like pattern. The alternative is to simply draw straight lines directly between the centers of each channel. + - Toggle whether to use a crosshair cursor if available. If the plot device supports a cross-hair cursor this will be substituted for the normal cursor if toggled on with the '+' key. Related commands ---------------- specopt - Preset specplot display options. specsmooth - Preset the spectral resolution displayed by specplot. specorder - Set the order in which spectra are to be displayed. specbase - Select the baselines to be displayed by specplot. specpol - Select the list of polarizations to be displayed by specplot. spectime - Select the time ranges to be displayed by specplot. specuvr - Select the UV radius ranges to be displayed by specplot.