[Gdal-dev] changing EPSG >> pixel resolution -- more clearly

[Ed McNierney]

Mattia -

Generally, no, it¹s not doable, at least not while maintaining unprojected
data.  A degree of latitude and a degree of longitude are not the same size,
and their sizes vary depending on where on the Earth they are located.  One
degree of longitude is a different size (in meters) at the northern edge of
your image than it is on the southern edge.

If you need to measure in meters you should project your image from
geographic coordinates to a projected coordinate system.  Your image covers
a fairly large area so you should think carefully about what projection is
best for your needs.

Or you could revisit your requirement; why you need an image with units in
meters?

     - Ed

-- 
Ed McNierney
President and Chief Mapmaker
Maps a la carte, Inc. / TopoZone.com
73 Princeton Street, Suite 305
North Chelmsford, MA  01863
Phone: (978) 251-4242
Fax: (978) 251-1396
ed at topozone.com


From: mattia <mattia.parigiani at gmail.com>
Date: Fri, 4 May 2007 17:51:41 +0200
To: gdal-dev <gdal-dev at lists.maptools.org>
Subject: [Gdal-dev] changing EPSG >> pixel resolution -- more clearly

Maybe I wasnt clear enough in my previous email:

My gdalinfo output on the new geotiff is:

rasdaman at mattia-desktop:/opt/rasdaman/local$ gdalinfo
250mGrey20070115065625.tif
Driver: GTiff/GeoTIFF
Size is 886, 883
Coordinate System is:
GEOGCS["WGS 84",
    DATUM["WGS_1984",
        SPHEROID["WGS 84",6378137,298.2572235629972,
            AUTHORITY["EPSG","7030"]],
        AUTHORITY["EPSG","6326"]],
    PRIMEM["Greenwich",0],
    UNIT["degree",0.0174532925199433],
    AUTHORITY["EPSG","4326"]]
Origin = (75.968700 ,53.448282)
Pixel Size = (0.03237320,-0.03237320)
Metadata:
  TIFFTAG_XRESOLUTION=100
  TIFFTAG_YRESOLUTION=100
Corner Coordinates:
Upper Left  (  75.9686998,  53.4482818) ( 75d58'7.32"E, 53d26' 53.81"N)
Lower Left  (  75.9686998,  24.8627462) ( 75d58'7.32"E, 24d51'45.89"N)
Upper Right ( 104.6513550,  53.4482818) (104d39'4.88"E, 53d26'53.81"N)
Lower Right ( 104.6513550 ,  24.8627462) (104d39'4.88"E, 24d51'45.89"N)
Center      (  90.3100274,  39.1555140) ( 90d18'36.10"E, 39d 9'19.85"N)
Band 1 Block=886x1 Type=Byte, ColorInterp=Gray
rasdaman at mattia-desktop :/opt/rasdaman/local$


I dont want degrees in Pixel Size = (0.03237320,-0.03237320) but I require
meters... Is this possibly doable??

Thanks again

-- 
Mattia

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