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On 03/31/2010 12:09 AM, Randy Bradley wrote:
<blockquote cite="mid:C7D7D2CD.9EA9%25Randy.Bradley@ars.usda.gov"
type="cite">
<title>Newbie... Locations, Projections, Regions, choices? (long)</title>
<font face="Calibri, Verdana, Helvetica, Arial"><span
style="font-size: 11pt;">All,<br>
<br>
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?<br>
<br>
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.<br>
> g.proj -p<br>
-PROJ_INFO-------------------------------------------------<br>
name : Latitude-Longitude<br>
datum : wgs84<br>
towgs84 : 0.000,0.000,0.000<br>
proj : ll<br>
ellps : wgs84<br>
-PROJ_UNITS------------------------------------------------<br>
unit : degree<br>
units : degrees<br>
meters : 1.0<br>
<br>
> g.region -p<br>
projection: 3 (Latitude-Longitude)<br>
zone: 0<br>
datum: wgs84<br>
ellipsoid: wgs84<br>
north: 49N<br>
south: 25N<br>
west: 125W<br>
east: 67W<br>
nsres: 0:00:30<br>
ewres: 0:00:30<br>
rows: 2880<br>
cols: 6960<br>
cells: 20044800<br>
<br>
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:<br>
<br>
> g.proj -p<br>
-PROJ_INFO-------------------------------------------------<br>
name : Albers Equal Area<br>
datum : wgs84<br>
towgs84 : 0.000,0.000,0.000<br>
proj : aea<br>
ellps : wgs84<br>
a : 6378137.0000000000<br>
es : 0.0066943800<br>
f : 298.2572235630<br>
lat_0 : 23.0000000000<br>
lat_1 : 29.5000000000<br>
lat_2 : 45.5000000000<br>
lon_0 : -96.0000000000<br>
x_0 : 0.0000000000<br>
y_0 : 0.0000000000<br>
-PROJ_UNITS------------------------------------------------<br>
unit : mile<br>
units : miles<br>
meters : 1609.3440000000<br>
<br>
> g.region -p<br>
projection: 99 (Albers Equal Area)<br>
zone: 0<br>
datum: wgs84<br>
ellipsoid: wgs84<br>
north: 49<br>
south: 25<br>
west: -125<br>
east: -67<br>
nsres: 0.05<br>
ewres: 0.05<br>
rows: 480<br>
cols: 1160<br>
cells: 556800<br>
<br>
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.<br>
<br>
</span></font></blockquote>
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:<br>
g.region vect=<states_vect> save=ConUS<br>
You might want to save this Continental zoom as the default with<br>
g.region -s ConUS <br>
Then zoom to each of the E,Central,W etc areas and save an additional
region, i.e. (after zooming to central region):<br>
g.region save=Central<br>
You can alternatively specify the region bounds with something like:<br>
g.region save=Central west=-120 east=-110 ...<br>
This all can be done in the GUI with Config->Region.<br>
<br>
Now you "jump" to each of the saved regions with<br>
g.region reg=Central <br>
etc...<br>
<br>
<br>
<blockquote cite="mid:C7D7D2CD.9EA9%25Randy.Bradley@ars.usda.gov"
type="cite"><font face="Calibri, Verdana, Helvetica, Arial"><span
style="font-size: 11pt;"><br>
Drowning in a sea of GRASS and loving it!<br>
<br>
Thanks for any<br>
suggestions,<br>
<br>
Randy</span></font>
<br>
<br>
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</blockquote>
<br>
<br>
<pre class="moz-signature" cols="72">--
Micha Silver
<a class="moz-txt-link-freetext" href="http://www.surfaces.co.il/">http://www.surfaces.co.il/</a>
Arava Development Co. +972-52-3665918</pre>
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