Tracing fringes

Frank Valdes wrote on May 04, 1999

Q:  I have been working on some data from a Shearing interferometer  (a bit
different to the usual data I gave) - tracing the fringes to examine the
wavefront. The aptrace task in twodspec.apextract seems the ideal thing
for this. But it would be much more useful to be able to write the pixel
positions along the peak of each traced `aperture' (ie interference
fringe) to a database rather than fitting a curve to them as the task
does. I have not found a way to do this - can you tell me if it is
possible.


A:  There has been several requests for a tool that lets one use the trace
in various ways such as making plots or getting lists of points.  This
is not currently possible.  You can evaluate the trace function as
described in "help aptrace" but you would need to write your own program
or use a calculator.

However, from what you describe I would suggest you look at the tasks
IDENTIFY and REIDENTIFY.  You would use IDENTIFY to mark postions of
the fringe or fringes in one cut across the image (you can cut in either
direction depending on the section parameter).  You can then use REIDENTIFY
to "trace" the fringe features across the detector.  The resulting output
is a database file, similar to the APEXTRACT database, that contains
the measured positions of the features at each point traced.  These
tasks were intended for tracing arc lines in 2D arc spectra and for
tracing the positions of objects on a slit (much as is done in APEXTRACT);
i.e. as part of measuring the geometry and dispersion function of long
slit exposures.  Your fringe data should be fairly similar.  The "features"
in the database file instead of being arc lines will be the fringes.
In your case there is no need to do the dispersion function fitting.

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Last post on May 04, 1999