Create a contour plot of a PSF kernel
contour_kernel([id,] [replot=False,] [overcontour=False]])
The contour_kernel command creates a contour plot of the kernel image. To plot multiple contour components at the same time (e.g. fit, source, and residuals), use the contour command ("ahelp contour"). To view the full, unfiltered PSF, use the image_psf command.
- id - the id of the dataset to use; if not given, uses the default dataset id (id=1 by default, see "ahelp get_default_id")
- replot - should the cached arrays be used in the plot? False (default)=do the calculation, True=redisplay the existing values
- overcontour - overplot the contour? default=False (clear the window before plotting)
The plot is displayed in a ChIPS plotting window. If there is no plotting window open, one is created. If a plotting window exists, the overcontour parameter value determines whether the new plot is overlaid on any existing plots in the window or if the window is cleared before the plot is drawn.
ChIPS commands may be used within Sherpa to modify plot characteristics and create hardcopies; refer to the ChIPS website for information.
What is the difference between the PSF and the kernel?
The point spread function (PSF) is defined by the full (unfiltered) PSF image loaded into Sherpa or the PSF model expression evaluated over the full range of the dataset; both types of PSFs are established with the load_psf() command. The kernel is the subsection of the PSF image or model which is used to convolve the data. This subsection is created from the PSF when the size and center of the kernel are defined by the command set_psf(). While the kernel and PSF might be congruent, defining a smaller kernel helps speed the convolution process by restricting the number of points within the PSF that Sherpa must evaluate.
Create a contour plot of the PSF kernel for the default dataset, using the default settings.
sherpa> contour_kernel("src", overcontour=True)
Make a contour plot of the PSF kernel for dataset "src", overplotting if there is an existing ChIPS window.