RPLOT: Radial Intensity Plot of an Object in an Image

Form: RPLOT imbuf [RAD=r[,c]] [CEN=r0,c0] [SCALE=s] [HARD]
[MIN=ymin] [MAX=ymax] [COLOR=c] [NOERASE] [LOG]
imbuf
Specify the image buffer. If no image buffer is given, the currently displayed image is assumed.
RAD=r[,c]
Set the radius of the box in pixels in both rows and columns. A second argument sets a rectangular box with the radius in Rows and Columns separately defined. (Default: RAD=5)
CEN=r0,c0
Define the central pixel for the radial intensity plot.
SCALE=s
Define the pixel scale in Arcsec/Pixel for the plot (does not apply to the RAD= keyword values)
HARD
Make a hardcopy of the radial intensity plot
MIN=, MAX=
Sets y-axis limits for plot
COLOR=
Set the color to be used for the plot
NOERASE
Do not erase between plots
LOG
Plot intensities on a logarithmic scale
This program makes a simple radial intensity plot of a section of an image. If the object is a star, it shows a mean point-spread function profile. An interactive version that works off the TV display is available via the TVRPLOT command.

The radial intensity plot is formed by finding the radius to all points within a given box around the specified location and plotting intensity versus radius. Each point making up the plot is from a single pixel; no interpolation is done. The effect is to produce an azimuthally wrapped (not averaged) plot of intensity. For example, if doing RPLOT on the image of a star, if that star is round, then a fairly clean radial point-spread function profile, will be plotted. If the star is elliptical (due to bad guiding or focus), the radial brightness profile will be a fuzzy cloud of points.

The center of the radial plot may be specified in one of two ways:

1.
The center is as defined in the AXES common block. You must have run the AXES command on the image before invoking RPLOT.
2.
The center is specified on the command line using the CEN= keyword.

Centers may be integer or fractional pixel values, but the size of the search region will be truncated to integer pixel intervals.

The interactive routine, TVRPLOT, allows the user to select the center of the radial plot with the interactive display cursor on the currently displayed image (see TVRPLOT). A hardcopy plot may be generated using the HARD keyword.

NOERASE suppresses erasing of the plotting window, allowing you to superimpose subsequent radial plots on top of each other.

LOG will plot the logarithm of the intensity as a function of radius.

COLOR=c changes the color of the points plotted. The default color is white (1). At present only the 7 "primary" graphics colors are available:

Color Codes
Code Color Code Color
  background 4 Blue
1 foreground 5 Yellow
2 Red 6 Magenta
3 Green 7 Cyan

Colors may be used in conjunction with NOERASE to overlay two different radial profiles, using the colors to distinguish them.

Examples:

RPLOT 1 RAD=10 CEN=51,25
Makes a radial intensity profile of the image in buffer 1 centered on the pixel at Row=51, Column=25, using all pixels within a 21x21 pixel wide box surrounding the center pixel.
RPLOT 1 RAD=10 CEN=51.5,25.2
Same as above, but the center of the plot is now at fractional pixel location (51.5,25.2)
RPLOT
Makes a radial intensity plot of the currently displayed image using the center computed by the previous AXES command (AXR and AXC variables). The box is 11x11 pixels (RAD=5) centered on (AXR,AXC).
RPLOT SCALE=0.54 HARD
Same as above, but scales the radii plotted to the pixel scale of 0.54 arcseconds/pixel, and sends the plot to the hardcopy device. The size of the box is still 11x11 pixels.