JITTERK

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.

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