[gdal-dev] gdalwarp resampling

[laura0]

Hi all,
I am going to use gdalwarp to resample a 800x800 wgs84 image but I did not
understand how to set output file resolution: gdalwarp description page says
to use the option -tr , but what does it mean with "in target georeferenced
units"?
This is my input image:

Size is 800, 800
Coordinate System is:
GEOGCS["WGS 84",
    DATUM["WGS_1984",
        SPHEROID["WGS 84",6378137,298.257223563,
            AUTHORITY["EPSG","7030"]],
        AUTHORITY["EPSG","6326"]],
    PRIMEM["Greenwich",0],
    UNIT["degree",0.0174532925199433],
    AUTHORITY["EPSG","4326"]]
Origin = (-115.730941999999999,-47.002102000000001)
Pixel Size = (0.039353161250000,-0.018197036250000)
Metadata:
  AREA_OR_POINT=Area
Image Structure Metadata:
  INTERLEAVE=BAND
Corner Coordinates:
Upper Left  (-115.7309420, -47.0021020) (115d43'51.39"W, 47d 0' 7.57"S)
Lower Left  (-115.7309420, -61.5597310) (115d43'51.39"W, 61d33'35.03"S)
Upper Right ( -84.2484130, -47.0021020) ( 84d14'54.29"W, 47d 0' 7.57"S)
Lower Right ( -84.2484130, -61.5597310) ( 84d14'54.29"W, 61d33'35.03"S)
Center      ( -99.9896775, -54.2809165) ( 99d59'22.84"W, 54d16'51.30"S)
Band 1 Block=800x2 Type=Float32, ColorInterp=Gray

I would like to resample it to a grid 12.5 km resolution and then (or in the
same time?) reproject into UTM (zone depending from coordinates), can anyone
help me? How should I express 12.5 km in the -tr option?
(the default resampling method nearest neighbor is fine for me).
Many thanks
Laura




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