XWindows

The operation thus requires the following:

• running software (called the XWindow server) on your local machine that will enable the local machine to receive output from the remote machine (this is only necessary if you are NOT sitting at a UNIX machine running XWindows already!);
• logging onto the remote machine from the local machine, and telling remote the name of local (so that remote knows where to send its output);
• and then running the (remote) software and getting the output on local.

1. At the University of Michigan, we use a commercial XWindow server called eXceed. If you have eXceed, then fire it up. This is a Windows operation (at UMich: Start -> Programs -> Terminal Emulators -> Exceed -> Exceed). If you don't see eXceed, do a find on your entire disk, and you may come up with it. eXceed will pop up a little window, which you can close.

   If you don't have eXceed, then there is a demo version of X-Win32 available, which you can install. It works pretty well for me! Alternatively, here is a weaker free server, but one which comes in Windows and Mac varieties!

2. Find the name of the machine at which you are sitting using the who command in your telnet session, looking for your username (which I will denote by my_username):
   

   who
   who |more
   who | grep my_username
   

   (try all three). The first command will probably spew out more info than you need; the second will page the output, so that none of it streams off the page before you have time to read it; while the third actually saves you the trouble of scanning, and just lists the lines that contain your username (grep is one of the UNIX pattern scanners - you know that someone is a UNIX person when they use "grep" as a verb: "Yeah, I grepped your meaning, there, buckeroo...").

3. set the DISPLAY variable, and export it so that other software invoked know it: first, find out what kind of shell you're using:

   echo $SHELL

   if you see the name "csh" or "tcsh" in the output of that command (most of you), then you will type

   setenv DISPLAY machine.name:0.0

   If you see the name "ksh", type

   DISPLAY=machine.name:0.0; export DISPLAY

   where machine.name is the machine name from the last who/grep line above. This should look like xerxes.sph.umich.edu, or perhaps like this: 198.108.20.8. At any rate, tack the :0.0 onto it and you've got a DISPLAY.

4. Before we do any damage, we'll want you to check that you've got enough space to play with: to do that at UMich (which uses AFS), you need to type

   fs lq

   once you get onto your machine, and check how many of your megs you have left. If you're at 90% or more of % Used, you're in space trouble and you'll have to be careful.

   Other places have other means of checking your quota. Check with your system administrator if you're worried.

5. Now we'll try some XWindow software (xv), which is extremely useful for image conversion. If you don't already have the file snow.gif, then you should download it to your computer and into your Unix account (right click on the link to save it to your computer). Type the following in your telnet session:

   xv snow.gif

   (Right click on the image to bring up a menu of operations.) Try using the Save button: save this image as a jpeg to your home directory.

   xv might prove useful in a variety of ways in this course, and is a handy piece of software in general. For example

   • you can "crop" an image (that is, cut out a portion of it): to do so, simply use your mouse to select a rectangular portion of the image, and then use the Crop button to eliminate all but that rectangle.
   • if you have an image that you want to digitize (that is, create an electronic map of it), you may have that image as in gif format, but need ppm format for import into your GIS.
   • gif and jpg are usually good formats for saving space. If you scan in an image that you want to save to your web site, it may be a tif (very large!). You can load it into xv and save it as a gif, thereby saving megs of space, and increasing access speed.
   • there is a limited amount of image processing that you can do with xv. If you want, try rotating the image slightly using the algorithm menu (the image is slightly askew), or try some edge detection....
   On the Windows side, there are applications like Adobe Photoshop for doing some of the same things; but for quick format transformation, nothing could be simpler.