sp - Make a scatter plot comparing two images			RWW & MWP


sp 1,2,1		Make a scatter plot of image 2 vs image 1 within
			area 1.  The results will be in the file "scatter" 
			in your home directory.

sp an:3 fn:"scatter3" yfact:1E-4 minx:.5
			Make a scatter plot with file named scatter3 in the 
			current directory using area 3 multiplying the 
			y values by 3 and suppressing data with x < .5 

sp logx: logy: miny:0 minx:0   
			Make a log-log plot of the images suppressing negative

sp ps:2 fill: ovl:	Plot with filled triangles instead of dots and overlay 
			on the current scatter plot. See 'gm ?!' for a list of 
			plot symbols and their figure numbers. See also note on
			plot symbols below.


Sp will produce a plot comparing two images using comb graphics. 
The default is a linear-linear plot with dots as symbols. Log-linear and 
log-log plots are also possible (this does not affect the printed output 
described below.) Other symbols as described in "gm ?!" are also available.

Sp produces a four column file suitable for plotting with mongo or
other package.  The four columns are x and y offsets from the image
center, the x image value, and the y image value.  The points will all
be from within the specified area.  The beginning of such a file

    -11      -21     0.3192    2.6e-07
    -10      -21     0.3849  2.571e-07
     -9      -21     0.3784  2.483e-07
     -8      -21     0.4007  2.424e-07
     -7      -21     0.4447  2.306e-07
     -6      -21     0.3818  2.189e-07

After making the graph, the integral of both images over the area is
shown on the standard output.  The value shown is the sum of the points 
times the area (in steradians) represented by each point in the map, e.g.:

Integral in x image is 0.000106336  [K-KM/S]*[SR] over 3.59618e-05 SR
Integral in y image is 7.77671e-12 [W/M2/SR]*[SR] over 3.59618e-05 SR

The integral is multiplied by the scale factor for that image.

Note for an integral with units [JY/BEAM]*[SR], you must divide
by the beam area in SR to get total JY. (Hint: use that number for
the scale factor.)

bmsr in .GMACROS will print out the beam area in steradians given
a FWHM in arcsec.


A list of figures and corresponding numbers is listed at the end
of "gm ?!".  If the given figure width and height (fw:, fh:) are 
zero (which is the initial value the first time you use "sp"),
then comb will scale them to the plot. Otherwise, the previous
value is used so that overlay plots (ovl:) come out looking nice. 
So if you want comb to re-compute the plot symbol sizes, just
give "fh:0" and "fw:0".

This document was last updated on Tue Oct 17 16:24:05 EDT 2000 by Marc W. Pound.