On 03/31/2010 12:09 AM, Randy Bradley wrote:
All,
I need to create 6 regional maps of the continental U.S., north
and south by west, central, and east. My first thought was to create
7 locations (one for the entire continental US) but my second thought
was to create just one location with the default region as the entire
continental US and 6 other regions. Is this sound logic?
First I downloaded the States data from the National Atlas. I
then created a latitude - longitude location and imported the shape
file excluding Alaska, Hawaii, Puerto Rico, and the Virgin Islands.
> g.proj -p
-PROJ_INFO-------------------------------------------------
name : Latitude-Longitude
datum : wgs84
towgs84 : 0.000,0.000,0.000
proj : ll
ellps : wgs84
-PROJ_UNITS------------------------------------------------
unit : degree
units : degrees
meters : 1.0
> g.region -p
projection: 3 (Latitude-Longitude)
zone: 0
datum: wgs84
ellipsoid: wgs84
north: 49N
south: 25N
west: 125W
east: 67W
nsres: 0:00:30
ewres: 0:00:30
rows: 2880
cols: 6960
cells: 20044800
The map displays fine but I want to change the projection to
Albers Equal Area or Lambert Conformal Conical since it is such a
large area. So I created a new location: aeaConUS with one caveat.
It said the eastern value had to be larger than the western value so
I (perhaps wrongly) used –125 for the western boundary and –67 for the
eastern. Using the GUI selected the “Vector>Develop map>Reproject
vector” menu item and selected the vector from the above location.
Here is what the new location and default region looks like:
> g.proj -p
-PROJ_INFO-------------------------------------------------
name : Albers Equal Area
datum : wgs84
towgs84 : 0.000,0.000,0.000
proj : aea
ellps : wgs84
a : 6378137.0000000000
es : 0.0066943800
f : 298.2572235630
lat_0 : 23.0000000000
lat_1 : 29.5000000000
lat_2 : 45.5000000000
lon_0 : -96.0000000000
x_0 : 0.0000000000
y_0 : 0.0000000000
-PROJ_UNITS------------------------------------------------
unit : mile
units : miles
meters : 1609.3440000000
> g.region -p
projection: 99 (Albers Equal Area)
zone: 0
datum: wgs84
ellipsoid: wgs84
north: 49
south: 25
west: -125
east: -67
nsres: 0.05
ewres: 0.05
rows: 480
cols: 1160
cells: 556800
When I first try to display this map, nothing is displayed unless
I select “Zoom display to selected map” at which point my nice Albers
map gets displayed. Or I can “zoom out” about 20 times to make the
Albers map start showing up near the top of the screen. Obviously I’m
doing something wrong here but I’m not sure if its the units (meters
vs miles) or something more fundamental.
It looks like you're off to a good start. All you need to do, in the
aeaConUs location, is save a few regions. Begin with:
g.region vect=<states_vect> save=ConUS
You might want to save this Continental zoom as the default with
g.region -s ConUS
Then zoom to each of the E,Central,W etc areas and save an additional
region, i.e. (after zooming to central region):
g.region save=Central
You can alternatively specify the region bounds with something like:
g.region save=Central west=-120 east=-110 ...
This all can be done in the GUI with Config->Region.
Now you "jump" to each of the saved regions with
g.region reg=Central
etc...
Drowning in a sea of GRASS and loving it!
Thanks for any
suggestions,
Randy
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--
Micha Silver
http://www.surfaces.co.il/
Arava Development Co. +972-52-3665918
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