NAME: jitterk PURPOSE: (one line only) Convert pointing jitter data into a convolution kernel. DESCRIPTION: This routine is intended to take time-tagged pointing history data and convert this to a convolution kernel that can be used to help model imaging data. The natural units of this routine is "pixels". The kernel is generated at this exact scale if SUBSAMPLE=1 (default). The units do NOT change if you set SUBSAMPLE to something other than 1. In that case you will get a kernel with higher spatial resoltion. Note that the units of dx,dy will be in pixels and will should not change with SUBSAMPLE. You should be able to take a model image at a matching sub-sampling factor, and convolve with the kernel returned from this routine to get a model image that matches the jitter history. CATEGORY: CCD data processing CALLING SEQUENCE: jitterk,dt,dx,dy,exptime,kernel INPUTS: dt - Vector, time from start of exposure. If first element is not dt=0 then (dt,dx,dy)=0 is assumed for the start. Units are in seconds. dx - Vector (same length as dt), pointing offset in pixels. dy - Vector (same length as dt), pointing offset in pixels. exptime - Exposure time for kernel, in seconds. The dt,dx,dy vectors should include exptime but is not enforced. Times outside dt will be extrapolated. OPTIONAL INPUT PARAMETERS: KEYWORD INPUT PARAMETERS: EXPCENTER - Flag, if set, the reference for the center of the jitter kernel is the mid-time of the exposure. The default is to use the mean dx,dy over the exposure. For true jitter kernels the default is best. For non-linear smearing due to parallax (with HST) it is better to set this flag. DTSAMPLE - time sampling interval (default=0.1 seconds) MOVING - Flag, if set takes out the mean velocity of the dx,dy trend with time. This is rarely used but would be relevant for a jitter-ball that is provided that includes jitter AND the target motion. Setting this will take out the mean motion and leave just the jitter. SUBSAMPLE - sub-sampling factor for kernel. Default=1 OUTPUTS: kernel - convolution kernel, will be square and will be normalized. KEYWORD OUTPUT PARAMETERS: COMMON BLOCKS: SIDE EFFECTS: RESTRICTIONS: The values of dx and dy are limited to "reasonable" values. Anything entry greater than 1000 is removed from the input vector. PROCEDURE: MODIFICATION HISTORY: Written by Marc W. Buie, Lowell Observatory, 2007/10/23 2014/09/23, MWB, updated documentation and added EXPCENTER option