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:
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:
| Code | Color | Code | Color |
| 0 | 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: