[GRASS-user] Re: getting started (stuck) with GRASS 2.

[LeeDaniel]

Hi Ruvy,

Don't worry, setting up the location is something that can even be difficult
for geographers that aren't familiar with GRASS. The concept is:

1. Geodata (data connected with locational information) consists of
descriptive information as well as data describing the object's position,
normally on the Earth's surface. That means coordinates. But because there
are multiple ways to describe positions on the Earth's surface, meaning
various coordinate systems, GRASS has to know what coordinate system your
data uses in order to be able to analyze your data in a spatial context.
2. In order to be more organized once a coordinate system has been defined
GRASS analyzes the data you import into various sub-categories that you can
organize as you like.

Practically, that means that you need to first define the coordinate system
you're working with. That's what you do in the "Location" GUI. In the first
GUI that pops up when you start GRASS, you tell GRASS where it should put
its database (the GIS Data Directory, field at the top) - that's a directory
that GRASS works with, where it will put all its data - including any data
you import and any data you produce. It sounds like you've already done
this.

After that you need to define a location that you'll be working in.
Locations can hold your data. All the data in a single location needs to use
the same coordinate system. If you have data with different coordinate
systems and want to be able to analyze or view them together in GRASS, it's
no problem, but you'll need to transform the data so that it all has a
single coordinate system. We won't worry about that. Let's worry about
getting you a working location first.

So the first step is to open the location wizard to create a new location.
If you click on that button it'll ask you what your new location should be
called - you can name it as you like - and after clicking "Next" you'll be
asked how you'd like to create your new location. As you're a landscape
architect I'm assuming you don't have too much experience with coordinate
systems and etc., which could make the next menu somewhat confusing. If you
know more information about the coordinate system you're working with, you
can enter that info. I'll assume you want to just take the coordinate system
of the data you've been given. Your first post sounded like you might have
already tried it, but I'll go through that quickly by describing two methods
that both work just as well:
- Select "Read projection and datum terms from a georeferenced data file"
and click next. Then enter one of your shapefiles (that's an Arc file with
the extension .shp). You could probably just as easily use the DWG file, but
since I've never tried that before we'll stick with the shapefile.
Alternatively, you can
- Select "Read projection and datum terms from a WKT or PRJ file" and click
next. Then take one of your *.prj files from the Arc data.

Now you should see a summary of the info you've entered. Click Finish and
you've got your location. In the interest of simplicity, don't set the
default region extents and resolution yet.

That's just step one, now you need a mapset to work in. Mapsets are inside
locations and contain data. You can have several datasets inside one mapset.
Mapsets can also interact with each other, as long as all the data's inside
the same location. Most users find it helpful to put data in mapsets that
either covers the same geographic area or is thematically related, but it's
really a matter of taste and effectiveness and must be decided from project
to project.

Normally I would always suggest making a new mapset to hold your data, but
since you don't have experience with GRASS and need your stuff quickly, we
can skip that and you can start working more "cleanly" later, after you've
gotten the GRASS book :) Once your location is made, you've got a mapset
automatically. It's called PERMANENT. Every location has a permanent mapset;
all other mapsets are added manually by the user. Let's use that one, so go
ahead and open it by clicking "Start GRASS".

Now you're in GRASS, and this is where I was talking about as I mentioned
"v.in.ogr" and "v.in.dwg". You'll have two windows, one is your layer
manager and the other is the map display, and if you type in "v.in.ogr"
without quotation marks in the "Cmd" field at the bottom of the layer
manager, you'll get the GUI for that module. It should let you import almost
any vector data format you want. I mentioned "v.in.dwg" after seeing your
data format and glancing over the results of a Google search, but I can't
find it either and in the documentation it seems to perhaps not exist any
more. I'm not sure what other options you have for that kind of data since I
don't know that format - it's for CAD data, right? There's probably a way of
importing it into GRASS, or of converting it into a format that can be
imported to GRASS, but I unfortunately can't help you much further in that
area.

Entering the commands in the command field is a great way to access them if
you know what commands you're looking for. But if you don't know them, you
can explore the menus in the layer manager - you'll find just about
everything you need there, plus descriptions. About your slope analysis:

GRASS does slope and viewshed analyses using rasters. For land use analyses
it depends a lot on what you want to do. If you've only got vector data, you
should import it into GRASS (v.in.ogr is the command), then convert it to a
raster (v.to.rast), then perform the analyses you need - you'll find the
commands you need in the "Raster" menu at the top of the layer manager.
Terrain analysis will be interesting for you (particularly r.slope.aspect),
as well as r.los for viewshed analyses.

Hope that helps! I know it's a lot of info at once, but I wanted to give you
something of a jump start if you need to have the analysis done within a few
days :)

Best regards,
Daniel
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