CHANNEL-MAPS

Produces a montage of contour maps of either the integrated or average intensity in a number of contiguous equal-width intervals. SET-MAP-SCALES can be used to determine the various axes. Thus although the most common use of this command is to contour a sequence of maps in adjacent velocity intervals, it is also possible to make a sequence say of RA-velocity maps in successive declination strips.

The maps cover intervals of the nominated width, beginning at the left hand end of the chosen range. I am not quite sure what happens if the interval and range are non-commensurate -- I suspect that only complete channels are plotted.

The contours are determined using SET-CONTOUR-LEVELS in manual mode -- it is not simple to autoscale over more than one image, while the use of different contours on the individual channel-maps would seem to be potentially confusing.

If desired you can alter the presentation of the channel maps (i.e.make them all stack vertically or horizontally), but the default option makes maximum use of the available plot area with the default 1:1 aspect ratio -- it may be necessary to set the plot sizes explicitly when plotting a sequence of position-velocity diagrams however.

The program integrates the intensity over the nominated range of the third ``z-axis'' coordinate (most commonly velocity), and if AVERAGE intensity over the range is selected then divides by the overall z-axis range to produce an average intensity (otherwise just the integrated total is plotted). If smoothing is selected in SET-MAP-PARAMETERS then the data plane is interpolated onto a finer sampling before plotting, which yields a more aesthetically pleasing image.

If zero sizes are selected in SET-MAP-SIZE then the routine uses the available graphics area to its fullest; if zero limits are selected in SET-MAP-SCALES then the routine plots the entire available data set.

Note that the routine only plots contours in ``cells'' which have real data at all four vertices. Thus if the map has 5-arcsecond cells, but only has measured data at 10-arcsecond sampling, then nothing will appear! Use INTERPOLATE-MAP to generate values for the missing points, and then CHANNEL-MAP.

There is no explicit command to make CHANNEL-MAP plot greyscales in addition to, or instead of, contours. This behaviour is controlled by the two logical variables PLOT_GREY and PLOT_CONT, which can be set and unset in the usual way (e.g.>> plot_grey=true). These variables are also set when doing a CONTOUR-MAP or GREYSCALE-MAP, so that contours will be the default after a CONTOUR and greyscales the default after GREYSCALE.

Relevant flags:

INTERACTIVE

L4

Enter interactive graphics mode after plotting.

LINTYP_POS

I4

Mongo line type for positive contours [0].

LINTYP_NEG

I4

Mongo line type for negative contours [1].

LINTYP_ZERO

I4

Mongo line type for zero contours [2].

LINE_WEIGHT

I4

Default line weight for plotting axes, labels etc [1].

NCONT

I4

Number of contours to be plotted.

CONTOUR_0

R4

Bottom contour.

CONTOUR_INT

R4

Contour interval.

NCSET

I4

Number of contours set manually.

CONTOUR_LEVS(16)

R4

Manually set contours.

AUTOGREY

L4

Set greyscale limits automatically from map max and min.

GREYLIM(2)

R4

Levels represented by black (min) and white (max)

COLOUR_TABLE

I4

Number of colour table to use

1	linear black to white
2	colour contours
3	power-law black to white
4	blue to yellow colours.
5	MRAO blue to white spiral

OVERLAY_CONTOURS

L4

Automatically overlay contours on greyscale

PLOT_GREY

L4

Plot greyscale for PLOT-LINE-PAR and CHANNEL-MAPS

PLOT_CONT

L4

Plot contours for PLOT-LINE-PAR and CHANNEL-MAPS

Examples:

    >> channel-maps<CR>
    Velo range? (km/s  ) [ -10.0000,  20.0000] <CR>
    Integrated intensity? (rather than average) (Y/N) [N] <CR>
    R.A. offset scaled from   80.000 to  -60.000
    Dec. offset scaled from   30.000 to  -30.000
    Channel width? (km/s  ) [     2.000] <CR>
    How many maps across page? (0=auto) [ 0] <CR>