Updates to the installation guide as requested from reviewers.

-->

  <h2>Overview</h2>

  <h3>ISIS3 Installation With Conda</h3>

    <p>The instructions for this are still being worked out.</p>

  <h3>Operating System Requirements</h3>

  <p>ISIS runs on many UNIX variants. ISIS does not run on MS Windows. The UNIX variants supported are listed here:</p>

  <p>ISIS3 runs on many UNIX variants. ISIS does not run natively on MS Windows,

     although it has been successfully run on Windows 10 using the Windows

     Subsystem for Linux (WSL).  Instructions for doing this can be found

     <a href="#RunningOnWindows">here.</a>

    The UNIX variants ISIS3 has been successfully built on are:</p>

    <ul>

      <li>Ubuntu 18.04 LTS</li>

      <li>Mac OS X 10.13.6 High Sierra</li>

      <li>Fedora 28</li>

    </ul>

    <p>ISIS3 is also build and tested nightly on the following operating systems.</p>

    <ul>

      <li>Ubuntu 14.04.3 LTS</li>

      <li>Debian Linux 8 (jessie)</li>

      <li>CentOS Linux 7.2.1511</li>

      <li>Fedora 25</li>

      <li>Mac OS X 10.11.6</li>

    </ul>

<p>

    ISIS3 maybe run on other operating systems then those listed above,

    but it has not been tested.

</p>

   <h3>Hardware Requirements</h3>

   <p>Here are the minimum hardware requirements</p>

    <ul>

      <li>64-bit (x86) processors</li>

      <li>2 GB memory</li>

      <li>10 GB to 180 GB disk space for ISIS installation</li>

      <li>2 GB RAM</li>

      <li>2.5 GB for ISIS3 binaries</li>

      <li>10 GB to 510 GB disk space for ISIS3 data</li>

      <li>10 GB to many TB disk space for processing images</li>

      <li>A quality graphics card</li>

    </ul>

<p>Note: More processors, memory, disk storage, and an additional graphcis card (to support the use of two monitors at

one time) may be useful depending on the complexity of your processing requirements

<p>Note: More processors, memory, disk storage, and an additional graphcis card

  (to support the use of two monitors at one time) may be useful depending on

  the complexity of your processing requirements.

</p>

<A NAME="RunningOnWindows"> </A>

<h3>Running ISIS3 on Windows 10</h3>

  <ul>

    <li><a href="https://docs.microsoft.com/en-us/windows/wsl/install-win10">Installing the Windows Subsystem for Linux</a></li>

    <li><a href="http://planetarygis.blogspot.com/2017/07/isis3-on-windows-10-bash.html">Instructions for using the Windows

      Subsystem for Linux (WSL) to run ISIS3</a></li>

  </ul>

  <p>

  While the ISIS3 development team has not examined these

  instructions for correctness or completeness, they appear to have

  successfully worked for a number of ISIS3 users within the USGS who run Windows.

  Thanks for these instructions are directed towards Trent Hare who maintains an

  excellent and thoughtful blog on <a href="http://planetarygis.blogspot.com/">Planetary GIS Science.</a>

  </p>

<A NAME="RunningOnWindowsWithSSH"> </A>

<h3>Setting Up X11 forwarding on Windows with Putty and XMing</h3>

<p>

Some ISIS3 users prefer to run ISIS3 in Windows, but SSH into a computer

that is running ISIS3 and has enabled X11 forwarding.  This requires the

installation of an X server on Windows.  Below are links to two popular choices

in Astrogeology.

</p>

  <ul>

    <li><a href="https://sourceforge.net/projects/xming/">Xming X server for Windows</a></li>

    <li><a href="https://sourceforge.net/projects/vcxsrv/">VcXsrv Windows X Server</a></li>

  </ul>

<p>

Additionally, a Windows SSH client is required to create an SSH connection.  PuTTY

is a popular choice and may be downloaded below.

</p>

<ul>

    <li><a href="https://www.putty.org/">PuTTY - an SSH and telnet client for the Windows platform.</a></li>

</ul>

   <h3>Mission Requirements</h3>

   <p>ISIS3 supports many planetary missions; in fact, over 40 different instruments including some

   flown as early as the 1960s.  Ancillary data are required to process images from these instruments.  For example, translation

   </p>

   <h3>DTM Requirements</h3>

   <p>The strength of ISIS 3 strength lies in its capabilities for planetary cartography.

   <p>The strength of ISIS3 lies in its capabilities for planetary cartography.

   The image orthorectification process is improved if a digital

   terrain model (DTM) is used.  The DTMs can be quite large and take some time to download.  They exist for

   many planetary bodies (e.g., the Moon, Mars, etc.). Therefore, there are options for selecting which DTMs to download

  <ul>

    <li><a href="https://github.com/USGS-Astrogeology/ISIS3/wiki/Developer-Checklists">ISIS3 Developer Checklist</a></li>

    <li><a href="https://github.com/USGS-Astrogeology/ISIS3/wiki/Jenkins-CI">Jenkins Continuous Integration Testing</a></li>

    <li><a href="https://github.com/USGS-Astrogeology/ISIS3/wiki/Managing-Custom-ISIS-Dependencies-(WIP)">Managing Custom ISIS3 Dependencies</a></li>

  </ul>

      </pre>

<p>

 Note:  The above command downloads all ISIS data including the required base data area and all of the optional mission

 data areas.  After completing this step, skip to the <a href="#UnixEnvironment">Unix Environment Setup</a>.  If you chose

 not to download everything at once then continue below.

 data areas.

</p>

        Guide</a> for instructions on downloading and installing ISIS3, version 3.5.2 or earlier.

    </p>

<A NAME="UnixEnvironment"> </A>

    <h2>UNIX Environment Setup</h2>

    <p>

        Still working on this part...

    </p>

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