HELP

[Irina Kosinovsky]

In info.grass.user you write:

>GRASS-netters,

>I hate to be a pain about this, but I really am stuck and *nobody* has
>replied to my earlier posts, so I'll try one more time.  Would anyone
>who has created GRASS databases on the hemispheric scale please contact
>me.  Here is the problem:

>I need to digitize a map of North and Central America that was produced
>by the USGS in 1982.  In order to do so, I have created a $LOCATION
>north_america.  The map is a transverse Mercator projection of the
>globe from 90N to 5N, 1:10,000,000 scale.  The central parallel is 45N
>and the central meridian is 100W with a scaling factor of 0.926.

>When I create the $LOCATION, how do I determine the corners of the
>region, e.g. at the DEFAULT_WIND input screen?  The tmerc projection
>demands that the corners be specified in meters, rather than lat-lon,
>so I measured the map edges, converted the measurements into meters on
>the ground, and entered the information as:

>N=8510000  S=0
>E=8770000  W=0


The way to do it is to take four corner points in lat/lon , convert
them to merc using m.proj or proj and enter the coordinates you
get (in meters) as your default region.(same thing when you define region
in v.digit)
The corner shouldn't be (0,0). You should gice the coordinates of all 4 corners.
m.proj asks you for latitude, longtitude and for all the parameters of
your projection and returns x and y in meters.
Please write me (irina at zorro.cecer.army.mil) if you have any question
I hope this helps.

Irina

>My guess is that the region definition is wrong, that the (0,0) point
>is actually at some fixed point on the globe (?) and that I need to
>define my DEFAULT_WIND relative to that fixed point, as would be the
>case if I were able to enter my initial coordinates in lat-lon.  If so,
>WHERE is that point?

Your guess is right. I am not sure where (0,0) is but m.proj will give you
the right coordinates.

>Alternatively, am I doing something else wrong?

I don't think so

>Would ANYONE who has successfully created a $LOCATION covering North
>America please contact me so I can find out how you did it.  Is it
>*possible* that no one has ever done this (hence the silence after my
>previous requests for help)?

>Thanks (hopefully...).

>%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

>Michael Camann                          camann at dial.pick.uga.edu
>Department of Entomology                camann at phoenix.cs.uga.edu
>University of Georgia                   (706) 542-1388
>Athens, GA 30602                        (706) 542-2276

>%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%