Defining the Area of Intervention

The Project AI (Area of Intervention) is defined by four of the Standard Topo Sheets "East Africa 1:50.000 (United Republic of Tanzania)":

• 55/1 Oldonyo Sambu
• 55/2 Engare Nanyuki
• 55/3 Arusha
• 55/4 Usa River.

These maps (geotiff) are georeferenced in Standard Arc 1960 UTM (EPSG:21037).

To obtain a single raster mosaic covering all the area:

1. ls -1 *.tif > tiff_list.txt
2. gdal_merge.py -v -o mosaic.tif --optfile tiff_list.txt

Then with:

• gdalinfo mosaic.tif

You can obtain:

Driver: GTiff/GeoTIFF
Files: mosaic.tif
Size is 13109, 13042
Coordinate System is:
PROJCS[" Projection Name = Arc_1960_UTM_Zone_37S Units = meters GeoTIFF Units = meters",
    GEOGCS["Arc 1960",
        DATUM["Arc_1960",
            SPHEROID["Clarke 1880 (RGS)",6378249.145,293.4649999999983,
                AUTHORITY["EPSG","7012"]],
            AUTHORITY["EPSG","6210"]],
        PRIMEM["Greenwich",0],
        UNIT["degree",0.0174532925199433],
        AUTHORITY["EPSG","4210"]],
    PROJECTION["Transverse_Mercator"],
    PARAMETER["latitude_of_origin",0],
    PARAMETER["central_meridian",39],
    PARAMETER["scale_factor",0.9996],
    PARAMETER["false_easting",500000],
    PARAMETER["false_northing",10000000],
    UNIT["metre",1,
        AUTHORITY["EPSG","9001"]]]
Origin = (222098.049999999988358,9668234.250000000000000)
Pixel Size = (4.250000000000000,-4.250000000000000)
Metadata:
  AREA_OR_POINT=Area
Image Structure Metadata:
  INTERLEAVE=PIXEL
Corner Coordinates:
Upper Left  (  222098.050, 9668234.250) ( 36d30'0.01"E,  2d59'56.28"S)
Lower Left  (  222098.050, 9612805.750) ( 36d29'55.57"E,  3d29'59.98"S)
Upper Right (  277811.300, 9668234.250) ( 37d 0'3.48"E,  3d 0'0.01"S)
Lower Right (  277811.300, 9612805.750) ( 36d59'59.92"E,  3d30'4.33"S)
Center      (  249954.675, 9640520.000) ( 36d44'59.74"E,  3d15'0.26"S)
Band 1 Block=13109x1 Type=Byte, ColorInterp=Red
Band 2 Block=13109x1 Type=Byte, ColorInterp=Green
Band 3 Block=13109x1 Type=Byte, ColorInterp=Blue

These are the limits (and other useful information) of the AI in Arc60, UTM and LatLong.

You can obtain a shapefile covering AI (EPSG:21037)with:

• gdaltindex mosaic.shp mosaic.tif

Now you can add a *.prj file to the shape with:

• ogr2ogr mosaic2.shp mosaic.shp -a_srs EPSG:21037

And read parameters with:

• ogrinfo -al -so mosaic2.shp
  

Links:

GDAL:

• http://www.gdal.org/
• http://www.gdal.org/gdal_utilities.html
• http://trac.osgeo.org/gdal/wiki/UserDocs

OGR:

• http://www.gdal.org/ogr/index.html
• http://www.gdal.org/ogr_utilities.html
  

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