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Basic Information on cgcurs
Task: cgcurs
Purpose: Read quantities with cursor from images on a PGPLOT device
Categories: plotting
CGCURS displays an image via a contour plots or a pixel map
representation (formerly called a "grey scale") on a PGPLOT
device. The cursor is then used to read image values, or to
evaluate image statistics in a polygonal region, or to write
a polygonal region definition to a text file.
Manipulation of the device colour lookup table is available
when you display with a pixel map representation.
When using cursor options, generally, click the right button
(enter X) to exit the function, click the left button (enter A)
to add a location, and click the middle button (enter D) to
delete a location.
Key: in
One or two input images may be specified. If two, and
TYPE=both, then the first is used as the background image, and
the second for a contour overlay. They must match in size.
Key: type
Specifies the type of the image(s) in the IN keyword. Minimum
match is supported:
"pixel": pixel map (formerly "grey" which is still supported),
"contour": contour plot,
"both": first input image is pixel map, the second is contour
overlay. If only one input image was specified it is
used for both.
Default is "pixel" if one input image is specified, else "both".
Key: region
Region of interest. Choose only one spatial region (bounding
box only supported), but as many spectral regions (i.e.,
multiple IMAGE specifications) as you like. If you display a
3-D image, the cursor options are activated after each sub-plot
(channel or group of channels; see CHAN below) is drawn.
Default is full image
Key: xybin
Up to 4 values. These give the spatial increment and binning
size in pixels for the x and y axes to be applied to the
selected region. If the binning size is not unity, it must
equal the increment. For example, to bin up the image by 4
pixels in the x direction and to pick out every third pixel in
the y direction, set XYBIN=4,4,3,1.
Defaults are 1,XYBIN(1),XYBIN(1),XYBIN(3)
Key: chan
2 values. The first is the channel increment, the second is
the number of channels to average, for each sub-plot. Thus
CHAN=5,3 would average groups of 3 channels together, starting
5 channels apart such as: 1:3, 6:8, 11:13 ... The channels
available are those designated by the REGION keyword. A new
group of channels (sub-plot) is started if there is a
discontinuity in the REGION selected channels (such as
IMAGE(10,20),IMAGE(22,30).
Defaults are 1,1
Key: slev
2 values. First value is the type of contour level scale
factor. "p" for percentage and "a" for absolute. Second
value is the level to scale LEVS by. Thus SLEV=p,1 would
contour levels at LEVS * 1% of the image peak intensity.
Similarly, SLEV=a,1.4e-2 would contour levels at LEVS * 1.4E-2
Default is no additional scaling of LEVS
Key: levs
Levels to contour for first image, are LEVS times SLEV
(either percentage of the image peak or absolute).
Defaults try to choose something sensible
Key: range
3 values. The pixel map range (background to foreground), and
transfer function type. The transfer function type can be one
of "lin" (linear), "log" (logarithmic), "heq" (histogram equal-
ization), and "sqr" (square root). See also OPTIONS=FIDDLE
which is in addition to the selections here.
Default is linear between the image minimum and maximum
If you wish to just give a transfer function type, set
range=0,0,heq say.
Key: device
The PGPLOT plot device, such as plot.plt/ps. No default.
Key: nxy
Number of sub-plots in the x and y directions on the page.
Defaults choose something sensible
Key: labtyp
Two values. The spatial label type of the x and y axes.
Minimum match is active. Select from:
"hms" the label is in H M S (e.g. for RA)
"dms" the label is in D M S (e.g. for DEC)
"arcsec" the label is in arcsecond offsets
"arcmin" the label is in arcminute offsets
"absdeg" the label is in degrees
"reldeg" the label is in degree offsets
The above assume the pixel increment is in radians.
"abspix" the label is in pixels
"relpix" the label is in pixel offsets
"abskms" the label is in Km/s
"relkms" the label is in Km/s offsets
"absghz" the label is in GHz
"relghz" the label is in GHz offsets
"absnat" the label is in natural coordinates as defined by
the header.
"relnat" the label is in offset natural coordinates
All offsets are from the reference pixel.
Defaults are "abspix", LABTYP(1) unless LABTYP(1)="hms"
whereupon LABTYP(2) defaults to "dms" (for RA and DEC).
Key: options
Task enrichment options. Minimum match is active.
"abspix" means write the region of interest in absolute integer
pixels instead of arcseconds relative to the reference pixel.
"box" When in "CURSOR" mode, rather than listing the value of
the of the pixel under the cursor, list the peak value in a
5x5 pixel box centred on the pixel under the cursor.
"cgspec" With OPTIONS=CURSOR and LOGFILE, the output log file
is is one with commands appropriate for input to CGSPEC's OLAY
keyword.
"cgdisp" With OPTIONS=CURSOR and LOGFILE, the output log file
is one with commands appropriate for input to CGDISP's OLAY
keyword.
Note that if you specify both CGSPEC and CGDISP then lines
appropriate to both these programs are written into the log
file. You can then copy the log file and retain the CGDISP
lines in one file, and the CGSPEC lines in the other.
"cursor" means that after drawing each sub-plot, a cursor will
be displayed; striking any key or clicking the relevant mouse
button (left) causes the location and value of the pixel under
the cursor to be listed on the terminal. On terminals, enter
"x" to exit the cursor. On workstations, click the relevant
button (generally the right one).
"fiddle" means enter a routine to allow you to interactively
change the display lookup table. You can cycle through b&w
and colour displays, as well as alter the transfer function by
the cursor location, or by selecting predefined transfer
functions such as histogram equalization, logarithmic, and
square root.
"grid" means draw a coordinate grid on the plot rather than just
ticks.
"logfile" When the "cursor" or "stats" are activated, then this
writes the results to log files (cgcurs.curs and cgcurs.stat)
as well as the screen.
"mark" When in "CURSOR" mode, mark the locations selected. If
OPTIONS=STATS is activated, mark the minimum and maximum pixel
locations too.
"nearest" When the cursor is used to select a location, force
that location to be the nearest image pixel, rather than the
default which allows fractional pixel locations.
"noerase" Don't erase a snugly fitting rectangle into which the
"3-axis" value string is written.
region means use the cursor to define a polygonal region that
gets gets written to a log file as the REGION keyword. The
cursor behaves as described above for the "stats" option. You
can the use this in other programs as "region=@filename"
"stats" means that after drawing each sub-plot, you get the
opportunity to define a polygonal region with the cursor (A to
add a vertex, D to delete the previous vertex, X to exit; or
use the three mouse buttons) inside of which image statistics
are evaluated.
"trlab" means label the top and right axes as well as the bottom
and left ones. This can be useful when non-linear coordinate
variation across the field makes the ticks misaligned
"unequal" means draw plots with unequal scales in x and y. The
default is that the scales are equal.
"wedge" means that if you are drawing a pixel map, also draw
and label a wedge to the right of the plot, showing the map
of intensity to colour
"3value" means label each sub-plot with the appropriate value
of the third axis (e.g. velocity or frequency for an xyv
ordered cube, position for a vxy ordered cube).
"3pixel" means label each sub-plot with the pixel value of the
the third axis. Both "3pixel" and "3value" can appear, and
both will be written on the plot. They are the average values
when the third axis is binned up with CHAN. If the third axis
is not velocity or frequency, the units type for "3VALUE" will
be chosen to be the complement of any like axis in the first
two. E.g., the cube is in vxy order and LABTYP=ABSKMS,ARCSEC
the units for the "3VALUE" label will be arcsec. If
LABTYP=ABSKMS,HMS the "3VALUE" label will be DMS (if the third
[y] axis is declination).
Key: 3format
If you ask for "3value" labelling, this keyword allows you
specify the FORTRAN format of the labelling. I have given
up trying to invent a decent algorithm to choose this. Examples
are "1pe12.6", or "f5.2" etc If you leave this blank cgdisp
will try something that you probably won't like.
Key: csize
Two values. Character sizes in units of the PGPLOT default
(which is ~ 1/40 of the view surface height) for the plot axis
labels and the velocity/channel labels.
Defaults choose something sensible.