Logging in

Your account should already be set up on the Spatlab UNIX cluster. You need a university UNIX account to use an X-terminal to log into our cluster. If you don't yet have an active University UNIX account hie thee to Smith hall, activate your account and select a username.

The class servers can only be accessed from Copland.  Open a Copland window on an X-terminal or PC Exceed.  First, use the xhost command to open your graphics display to the class server; then telnet to aesop:

> xhost +aesop.ags.udel.edu
aesop.ags.udel.edu being added to access control list
> telnet aesop.ags.udel.edu

Enter your Aesop login and password.  Now have Aesop open a separate graphics-capable X-window on your display:

> xterm -display $DISPLAY

You should see a new X-terminal window pop up on your screen.

Starting a GRASS session

To begin a GRASS session in your X-window, type grass at the prompt in this X-terminal window.

If you are a first-time GRASS user you will see a welcome screen. Hit ENTER. You will then see the usual GRASS start-up screen. You need to fill in the three fields highlighted in green in the image below: start with the "spearfish" location, your login name as your mapset (or specify another name you want to use), and home/grass.data as the database path (don't forget the leading "/" character).

Note that on this screen, as in most GRASS set-up screens, the Enter key advances you through the screen items. The ESC-Enter key sequence terminates screen entry and executes the parameters. This takes a little getting used to.

Unless you have some particular reason to resize your command window, it is generally best not to do so. Some GRASS menu screens are defined for a standard X window, and look confusing in re-sized windows.

After you close the start-up screen with ESC, you will see the GRASS prompt, telling you your current location (Spearfish) and mapset name.

Display monitors

The Aesop GRASS server supports graphic display monitor windows named X0 through X16. You should generally only use one monitor process at a time: you can always split a large display window into separate frames with d.frame if you want to display multiple maps at once.

Open a display "monitor" window with the d.mon module:

• d.mon -L lists the status of the monitors
• d.mon start=x2 starts monitor x2 on your screen (assuming someone else isn't already using it).
• d.mon stop=x2 terminates x2. (Remember to stop your display monitor before exiting GRASS; otherwise you are likely to leave monitor lock files in place which will make the monitor unavailable for any other users.)

Now you're ready to start playing with some maps.  First, you should set your region with the g.region module.  Here we use the region parameters from an existing map:

GRASS > g.region rast=elevation.dem

After changing your region, you must refresh your monitor; then you can display some stuff:

GRASS > d.erase
GRASS > d.rast elevation.dem
GRASS > d.vect roads color=black
GRASS > d.vect streams c=blue

GRASS modules

Note that GRASS modules are sorted into general categories:

• Display module names begin with "d." e.g. d.mon, d.erase, d.rast, d.vect
• General utility modules begin with "g."
• Image processing modules begin with "i."
• Data processing modules begin with "m."
• Hardcopy generation modules begin with "p." or "ps." (Postscript)
• Raster processing modules begin with "r."
• Sites (point feature) processing modules begin with "s."
• Vector processing modules begin with "v."

Now you are ready to start trying out some basic modules.  First check out the on-line help utilities:

• UNIX man pages are available for any UNIX command.  To see the documentation for the ls command, for example, type man ls at the prompt.
• GRASS command help for syntax.  You can get a quick summary of any command's syntax and options by typing the command followed by "help"
• g.manual access the on-line version of the manual providing complete documentation of GRASS modules.
• g.help offers detailed descriptions of standard GIS operations in GRASS, organized by topic
  
  Try exploring the following modules:

• g.list rast/vect/sites
  
  
• Display modules:
• d.rast map
• d.vect map color=
• d.sites map type= color=
• d.3d   Try draping raster map spot.image over elevation.dem. Work with a somewhat coarse grid which paints quickly until you get the best view, then display the final version as a fine-resolution drape.
  
  
• regions:
• g.region: check out the options.
• d.zoom, d.rast.zoom
  Zooming resets your current region. Use g.region to un-zoom.)

• Location Queries:
• d.what.rast map1,map2,... > outfile
• You can query multiple maps at once, outputting the results to a text file for statistical analysis or whatever.)
• d.where
  
  
• Distance Queries:
• d.measure
• d.geodesic (only works on lat-long; try it in the "global" location)
• d.rhumbline
• d.profile
• d.histogram

If you want to switch locations, you have to exit GRASS and restart in the new location. In this case you can leave your GRASS monitor running, and simply select it with d.mon after restarting.

When terminating your work session, after exiting GRASS type "exit" again to log off the Spatlab server. Its X-window should disappear.  If you are working on an X-terminal, you must terminate your X-terminal session by choosing "Quit and Logout" from the X-terminal menu (left mouse button anywhere on blue screen). Make sure the X-terminal login window reappears on the screen so you are certain you are fully logged off.