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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>
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