Subject: Viewing Fits Files: Bill and Tom

From: Gordon <dgb at doplar.wa.astro.gov.au>
Date: Mon, 11 May 1998 12:55:21 +0800

Success at last.  

Bill and Tom thanks for your help, now I am able to view FITS files
downloaded from the Skyview site.   

Bill, I tried the address you gave me for the exe file but I coudn't get
a response so I went to the NRAO Home Page and searched around until I
found one.  The address of that file is:

ftp://ftps.cv.nrao.edu/fits/os-support/ms-windows/fitsview/win16/

In an e-mail, I was told that the data from stdatu.stsci.edu/dss/ has
problems with coordinates but image quality was good.  How inaccurate
are they?  Should I use the Skyview site knowing its images are poor in
comparison but coordinates OK.  I guess it depends on what I want to use
the data for.  

Thanks again guys.

Gordon

---

From: Tom McGlynn <tam at silk.gsfc.nasa.gov>
Date: Mon, 11 May 1998 10:19:00 -0400

> comparison but coordinates OK.  I guess it depends on what I want to use

The two sites do different things:  ST's page gives you the data directly
as scanned from the plates -- though the image compression algorithm has been
applied. Thus the coordinate system for the image is a fragment of a Schmidt plate and
not one of the simple projections that most software understands.

SkyView resamples the image into the coordinate system you specify so that
it can provide the data in more standard coordinate frames and you can also
rescale the image or mosaic different plates.  However,
the DSS images have 1.7" pixels which is really a bit undersampled, so that
when it is resampled by SkyView there can be artifacts from the process
(i.e., occasionally an object will be distorted when a pixel is skipped or
hit twice in the resampling).  This is discussed  a bit on the SkyView, What's New
page entry from 19 Oct, 1994.  You can minimize this by using the linear
interpolation resampling, but that will blur things a little bit.

This has strayed a ways from FITS.  If you're interested in further information
about SkyView please let me know.

		Yours,
		Tom McGlynn
		tam at silk.gsfc.nasa.gov