The following ''PSF tools'', in addition to their imaging functions, are also used to access the grating LSF's. Hence, in this section PSF and LSF are used interchangeably. These exist both as user callable programs and as subroutines that can be called from within other programs (eg. the ARFtool).
PSF_model requires the position of the zero order, energy, order, grating, and projection direction to determine which lsf in the library files to retrieve. If no lsf image is available at that particular position then the tool will interpolate between images in the library to obtain the best lsf to return. The order of the interpolation is to first linearly interpolate in position the four images which enclose the requested postion to obtain images at the two energies that bracket the input energy. Then these images are linearly interpolated in energy to the requested energy to obtain the final image. The final image is then resampled to the bin size requested or it can be returned with the original sampling of the library. The lsf is passed back to the calling program as a FITS image.
PSF_Frac integrates a LSF image, supplied by psf_model, within a given radius or region to obtain the fraction of the PSF within that radius. The inputs for psf_frac are the same as psf_model, since it calls psf_model to obtain the input image, with the addition of an input radius or a region mask. If a radius is given the the PSF will be integrated out to and including that radius, and if a region mask is input the the PSF fraction is the total counts within the mask divided by the total counts in the PSF/LSF image.
PSF_SIZE uses the encircled energy tables to provide an estimate of the size of the psf. The inputs are the same as those for psf_model with the addition of an EE fraction. This program uses the EE tables, instead of calling psf_model, and interpolates the EE tables in the same manner, linear interpolation in the same order as psf_model interpolates the images. This interpolated EE table is then read to determine at what radius the input EE fraction is obtained.