PISA demonstration

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PISA demonstration

This page displays various snapshots and explanations of the PISA rolling demonstration "pisa_demo". PISA is a group of applications (a package) that deal with the location and parameterisation of objects on an image. The core of this package is an application called PISAFIND. This analyses 2-D images searching for groups of connected pixels above a given threshold. It extracts these pixels and parameterises them into various measures of position, intensity and ellipticity. In crowded fields merged objects can be deblended. PISAFIND is based on the APM IMAGES program that was written by Mike Irwin of the University of Cambridge. PISA is documented in SUN/109.

A run of PISAFIND on the image displayed above produces a results file, that can be plotted as below.

Note the object "deblending" that has occurred in the crowded central regions.

PISA can use an analytic stellar profile to fit stars.

The parameters produced by the fit can subsequently be used to fit all the stars on a frame (useful if they are low-intensity).

The results from PISAFIND can also be used to generate model data to which noise can be added.

PISA can help in the classification of objects. This uses a peakedness measure (that essentially tells you how stellar an object is) together with other parameters that are intensity invariant (at least in principle). The example shown here simply uses a cut in peakedness to separate out stellar (red) from non-stellar (green) objects.

Questions or comments to: p.w.draper@durham.ac.uk.

Copyright © 2005 Central Laboratory of the Research Councils
Copyright © 2006 Particle Physics and Astronomy Research Council
Copyright © 2008-2009 Science and Technlogy Facilities Council
Copyright © 2009-2013 Peter W. Draper
Last modified: 02-Jun-2016
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