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<title>Virtual Observatory</title>
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<h3><img alt="" src="../sun.gif" align="middle" width="100" height="98">
Virtual Observatory Reference</h3>
<blockquote>
<p><b>Summary</b></p>
<p>Use the Web proxy connection if your firewall does not allow your
computer to connect directly to external computers. In this case, you
also must use DS9's internal browser.</p>
<p><b>Details</b></p>
<p>When you click on one of the Virtual Observatory servers in the VO
list, DS9 will attempt to connect to that server and (if the internal
Web display is enabled) display its Web page. The square box to the left
of the server name turns yellow while the connection is being
established and then green to signal success. </p>
<p>A direct connection is fast and flexible. Among other things, it
allows
you to perform analysis on your own local data (the VO server will
retrieve the image from DS9) and also allows you to use an
external browser to load images. </p>
<p>Some system managers configure their firewall explicitly to
prevent
computers in their care from making a direct connection to an external
host. Instead, they only allow external access through a Web proxy<br>
server (such as SOCKS). If you are using a computer behind a restricted
firewall of this sort, then DS9 will not be able to connect directly to
a VO server. The yellow box will not turn green and
eventually DS9 will display an error message. </p>
<p>In this case, you can choose to have DS9 communicate with the VO
servers through your Web proxy server. DS9 will use your proxy to send
its commands and retrieve its data and analysis results, rather than
doing this directly. Note that the following restrictions apply:<br>
</p>
<blockquote> <i>The transfer of data is slower.<br>
You must use the internal Web browser for loading images, etc.<br>
You cannot perform analysis on local data.<br>
There is a (large but finite) restriction on the number of
annuli, and number of polygon points you can specify in a region, as
well as the total number of regions allowed.</i><br>
</blockquote>
<p>If your computer and firewall have been configured to require use
of a
Web proxy server, you will have to tell DS9 about this server.
Click the <b>Configure Web Proxy</b> button and type the relevant
information into the boxes. (Your systems administrator will be able to
tell you the details.) At this point,
you should be able to connect to a VO server successfully. Please let
us know if you have problems! </p>
<blockquote>
<p> <i>A final note: you may, of course, choose to use the Web
proxy
even
if your computer and firewall are configured to allow direct
connections. In this case, there is no need to configure the proxy
server.<br>
</i></p>
</blockquote>
</blockquote>
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