[GRASS-user] Newbie... Locations, Projections, Regions, choices? (long)

Randy_Bradley · March 30, 2010, 9:09pm

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.

Drowning in a sea of GRASS and loving it!

Thanks for any
suggestions,

Randy

Achim_Kisseler · March 31, 2010, 7:16am

Hi Randy,

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?

Just a personal suggestion:
Here I suggest to create one location with 6 mapsets if you have huge vector maps. You can store the basic data in PERMANENT. Otherwise just create one mapset, make your map and zoom to the areas of interest. Here you can store combination of layers and how they are displayed as "workspaces".

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.

done well

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

This is a problem I have, too.

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.

I don't know why this happens. Its not the meters-miles thing. Exporting and importing helps, but that's not a real solution.

Achim

Achim_Kisseler · March 31, 2010, 7:23am

Hi Randy,

> 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?

Just a personal suggestion:
Here I suggest to create one location with 6 mapsets if you have huge vector maps. You can store the basic data in PERMANENT. Otherwise just create one mapset, make your map and zoom to the areas of interest. Here you can store combination of layers and how they are displayed as "workspaces".

>
> 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.

done well

>
> 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

This is a problem I have, too.

> 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.
>

I don't know why this happens. Its not the meters-miles thing. Exporting and importing helps, but that's not a real solution.

Achim

Micha_Silver · March 31, 2010, 7:57am

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…

···

-- 
Micha Silver
[http://www.surfaces.co.il/](http://www.surfaces.co.il/)
Arava Development Co.  +972-52-3665918

Randy_Bradley · March 31, 2010, 6:30pm

On 03/31/10 2:57 AM, “Micha Silver” micha@arava.co.il wrote:

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…

Thanks Micha. Good to know I’m on the right course. After the first step: “g.region vect=States save=ConUS” I can indeed “zoom to saved region” in the display to view the map. However, g.region region=ConUS shows:

projection: 99 (Albers Equal Area)
zone: 0
datum: wgs84
ellipsoid: wgs84
north: 1838.08985202
south: 34.12860299
west: -1467.66023444
east: 1403.23869107
nsres: 0.05000031
ewres: 0.04999998
rows: 36079
cols: 57418
cells: 2071584022

Unfortunately, the bounds are all offset from the central axis so I can’t use the lat. & lon. values for the boundaries as you suggest. (ie west=-120 east=-110) I can overlay a grid and get a good estimate of values that will work to define my regions.

Glynn_Clements1 · March 31, 2010, 7:15pm

Randy Bradley wrote:

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
³Vector>Develop map>Reproject vector² menu item and selected the vector from
the above location. Here is what the new location and default region looks
like:

> g.region -p
projection: 99 (Albers Equal Area)

north: 49
south: 25
west: -125
east: -67

For a projected location, the bounds must be specified in projected
coordinates (metres, feet, etc), not lat/lon degrees.

--
Glynn Clements <glynn@gclements.plus.com>