[GRASS-user] Help with reprojection

[José María Michia]

2009/1/2 Alex Bernstein <pofig37 en gmail.com>:
> Hi,

Hello Alex!

> I'm new to GRASS, and am having trouble with reprojection. I've spent
> two days trying to figure this out, and I feel that I'm close, but
> reprojection is still failing. Could anyone clue me in what I'm
> missing?

I will try to give a bit of help here. I'm very limited by idiomatic issues.

> The input data set is Natural Earth II map of the world
> <http://www.nacis.org/data/NE2/NE2_WDB1.jpg> 16200x8100 JPG in plate
> carrée projection. I need to reproject it into Lambert azimuthal
> equal-area projection centered on N0 E15. I'm using WinGRASS 6.3.0.
>
> First, I've created GRASS location "geographic" with following region
> and projection:
>
>> g.region -p
> projection: 99 (Equidistant Cylindrical (Plate Caree))
> zone:       0
> datum:      wgs84
> ellipsoid:  wgs84
> north:      8100
> south:      0
> west:       0
> east:       16200
> nsres:      1
> ewres:      1
> rows:       8100
> cols:       16200
> cells:      131220000

I think thath you have problems in projection and region definition.

You must check your region parameters. Geographic coordinates must be
in the following ranges:

north, south: [-90, 90]
west, east:  [-180, 180]

Fix your region with something like:

> g.region -p n=90 s=90 w=-180 e=180

But ... There is another problem. Your "Location" was created badly.

A "Location" in geographic coordinates, must :

> g.region-p
projection: 3 (Latitude-Longitude)
....

(I don't know which projection is "projection: 99 ...". If someone
knows, please, tell me.)

You must begin again. Start "grass", and click "EPSG Codes". In the
next window, enter the code 4326, which is the correct value to use
geographical coordinates. Import your JPG image in this location.
(see images attached)

>> g.proj -p datumtrans=0
> PROJ_INFO-------------------------------------------------
> name       : Equidistant Cylindrical (Plate Caree)
> datum      : wgs84
> towgs84    : 0.000,0.000,0.000
> proj       : eqc
> ellps      : wgs84
> a          : 6378137.0000000000
> es         : 0.0066943800
> f          : 298.2572235630
> lat_0      : 0.0000000000
> lat_ts     : 0.0000000000
> lon_0      : 0.0000000000
> -PROJ_UNITS------------------------------------------------
> unit       : meter
> units      : meters
> meters     : 1.0
>
> I then imported the JPG map, which got split into color channels and
> composed the channels together into single map.
>
> After, I created a new location "lambert":
>> g.region -p
> projection: 99 (Lambert Azimuthal Equal Area)
> zone:       0
> datum:      wgs84
> ellipsoid:  wgs84
> north:      8100
> south:      0
> west:       0
> east:       16200
> nsres:      1
> ewres:      1
> rows:       8100
> cols:       16200
> cells:      131220000
>
>> g.proj -p datumtrans=0
> -PROJ_INFO-------------------------------------------------
> name       : Lambert Azimuthal Equal Area
> datum      : wgs84
> towgs84    : 0.000,0.000,0.000
> proj       : laea
> ellps      : wgs84
> a          : 6378137.0000000000
> es         : 0.0066943800
> f          : 298.2572235630
> lat_0      : 0.0000000000
> lon_0      : 15.0000000000
> x_0        : 0.0000000000
> y_0        : 0.0000000000
> -PROJ_UNITS------------------------------------------------
> unit       : meter
> units      : meters
> meters     : 1.0
>
> Finally, when I try reprojection I get "Input raster map is outside
> current region" error:
>> r.proj input=NE2 location=geographic mapset=PERMANENT method=cubic
> Input Projection Parameters:  +proj=eqc +lat_0=0.0000000000
> +lat_ts=0.0000000000 +lon_0=0.0000000000 +a=6378137 +rf=298.257223563
> +no_defs +towgs84=0.000,0.000,0.000
> Input Unit Factor: 1
> Output Projection Parameters:  +proj=laea +lat_0=0.0000000000
> +lon_0=15.0000000000 +x_0=0.0000000000 +y_0=0.0000000000 +a=6378137
> +rf=298.257223563 +no_defs +towgs84=0.000,0.000,0.000
> Output Unit Factor: 1
> Input raster map is outside current region
>
> How can I make this work?
> Thanks,
> Alex

If this helps you, maybe i can try to give a bit more of help.

Saludos
José María
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