| Free SAR Geocoding Software [message #19856] |
Tue, 18 April 2000 00:00 |
Andy Sowter
Messages: 4
Registered: February 1999
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Junior Member |
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Free SAR geocoding software, Ellipse 1.1, is available via the following
website:
http://www.synopticsga.freeserve.co.uk/geocode/ellipse.htm
The reason for free distribution to the public follows trials held within
sister companies and the Joint Research Centre, Italy and the agreement that
there is a need to promote a more automated approach to spaceborne SAR
Geocoding. SAR is unique in that automated geocoding is possible, unlike,
for example, most optical sensors.
This release has not been funded in any way and is, therefore, a little
rough around the edges! However, it works. If it stimulates enough
interest, there may be further releases (perhaps even terrain correction).
Technical Overview
---------------------------
This software allows the automated ellipsoid correction of an ERS SAR PRI
image using a full range doppler solution. Such a solution is more accurate
than warping using corner coordinates and is fully automated. The results
should be within 25m (2 pixels) of error.
The software will select the UTM Zone dictated by the centre coordinates of
the image and will output a 16-bit integer array at 12.5m pixel spacing in
those coordinates, using the WGS-84 ellipsoid as reference. The resampling
method used is Nearest Neighbour.
The Software
------------------
The software is provided as an IDL executable (.SAV) and was developed under
IDL 5.2. Information about IDL may be found at:
http://www.rsinc.com
The software is installed using the RESTORE function and executed by the
single command
go_ellipse
at the IDL command line
It is based on some in-house terrain correction software and has not been
optimised for speed. Furthermore, it reads the whole PRI image into memory
(some 130MB).
On a P450, 256MB RAM, it takes about 2 hours to complete a full scene.
The output files are as follows:
- A text file containing a dump of the PRI image header.
- A generic binary data file containing the geocoded image in 16-bit integer
format.
Assumptions
-----------------
The input file is assumed to be fully compliant with the ESA CEOS Harmonised
format described in:
"ERS SAR.PRI CCT and EXABYTE", European Space Agency document:
ER-IS-EPO-GS-5902.4, Issue: 2.1, Date: October 2, 1995, Prepared by: Ola
Grabek, Checked by: H Laur.
Any deviation from this format (such as a variable length Platform Position
Data Record, which is common outside of Europe) will result in errors. The
author is confident that the software will work using PRI data output by any
of the ESA Processing and Archiving Facilities in Europe.
The Author
---------------
Andy Sowter has been designing SAR ortho-rectification requirements since
1988 and has been pioneering tiepoint-free methods for spaceborne SAR
sensors, such as ERS and Radarsat. Recently, he has designed and
implemented a method for generating DEMs from Radarsat stereo pairs without
ground control.
Andy does NOT describe himself as a programmer!!
Further information may be found at:
http://www.synopticsga.freeserve.co.uk
(c) Synoptics Geo Applications Limited, 2000. All rights reserved.
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