I sympathize because I went through this.
Here's the answers:
(Q) How do I come up with all of that information
necessary to creating a database?
(A) Check the Metadata for the data set. The Metadata
should contain the projection, datum and ellipsoid
data. See examples at bottom.
(Q) Back when I first set my GRASS database up, I read
somewhere that I should use the wgs84 ellipsoid.
How do you know which to use, and what happens if
you use the wrong one?
(A) The meta data may have the ellipsoid data. However,
the ellipsoid is tied to the datum. For a given datum,
a certain ellipsoid is used. In the US, NAD83 datum
uses GRS80 ellipsoid and NAD27 uses Clarke66 (as in
1866). Search the web and read about Datum and
Ellipsoid. If you get it wrong, nothing happens.
Grass shows everything in its display as X,Y data.
The importance of getting it correct is if you
transform from one datum or projection to another
or if you try to display 2 different datum or
projections in the same mapset and expect them to
line up.
(Q) Since I don't have a database setup yet, I can't
run the GRASS commands to get information from the map data.
(A) Doesn't matter too much. Just set up a location.
Let's say you have sdts data you want to import.
use m.sdts.read to read the files. Poke around and
you will find the metadata you need. If your location
isn't correct, stop grass and restart creating the
location you need. No harm done.
The nice thing about the spearfish data set is that you can
start with something and play till your hearts content. I
loaded in all kinds of stuff: geotiff, bil, shape files, DRG,
DLG till I figured out what I was doing. It won't break
anything. You can erase it later if you want.
---------------------
EXAMPLES:
Spatial_Reference_Information:
Horizontal_Coordinate_System_Definition:
Horizontal_Coordinate_System: Grid
Grid_Coordinate_System_Name: UTM
Planar_Distance_Units: METERS
one_Number: 19
Horizontal_Datum_Name: NAD83
Ellipsoid_Name: GRS1980
X-Shift: 0.0000000000
Y-Shift: 0.0000000000
Spatial_Reference_Information:
Horizontal_Coordinate_System_Definition:
Planar:
Map_Projection:
Map_Projection_Name: Albers Conical Equal Area
Albers_Conical_Equal_Area:
Standard_Parallel: 55
Standard_Parallel: 65
Longitude_of_Central_Meridian: -154
Latitude_of_Projection_Origin: 50
False_Easting: 0.00000
False_Northing: 0.00000
Planar_Coordinate_Information:
Planar_Coordinate_Encoding_Method: coordinate pair
Coordinate_Representation:
Abscissa_Resolution: 1.0
Ordinate_Resolution: 1.0
Planar_Distance_Units: METERS
Geodetic_Model:
Horizontal_Datum_Name: NAD27
Ellipsoid_Name: Clarke 1866
Semi-major_Axis: 6378206.4
Denominator_of_Flattening_Ratio: 294.98
