[gdal-dev] how can a Geotiff occupy three times the disk space of an ASCII Grid?

[G. Allegri]

I've converted a Float32 ASCII Grid of 8861 x 9457 cells to Geotiff (with
deflate compression, predicor=1).
The original file was 577 MB, the resulting Geotiff is about 1.897 MB.

Here is gdalinfo run on the ASCII:

Driver: AAIGrid/Arc/Info ASCII Grid
Files: DTM\dtm.asc
       DTM\dtm.asc.aux.xml
Size is 8861, 9457
Coordinate System is `'
Origin = (1634712.000000000000000,4904391.000000000000000)
Pixel Size = (10.000000000000000,-10.000000000000000)
Corner Coordinates:
Upper Left  ( 1634712.000, 4904391.000)
Lower Left  ( 1634712.000, 4809821.000)
Upper Right ( 1723322.000, 4904391.000)
Lower Right ( 1723322.000, 4809821.000)
Center      ( 1679017.000, 4857106.000)
Band 1 Block=8861x1 Type=Float32, ColorInterp=Undefined
  Min=5.810 Max=1932.780
  Minimum=5.810, Maximum=1932.780, Mean=393.467, StdDev=316.141
  NoData Value=-99
  Metadata:
    STATISTICS_MAXIMUM=1932,78
    STATISTICS_MEAN=393,46740210782
    STATISTICS_MINIMUM=5,81
    STATISTICS_STDDEV=316,14065359461

And here the Geotiff:

Driver: GTiff/GeoTIFF
Files: dtm.tif
Size is 8861, 9457
Coordinate System is:
PROJCS["Monte Mario / Italy zone 1",
    GEOGCS["Monte Mario",
        DATUM["Monte_Mario",
            SPHEROID["International 1924",6378388,297.0000000000014,
                AUTHORITY["EPSG","7022"]],
            AUTHORITY["EPSG","6265"]],
        PRIMEM["Greenwich",0],
        UNIT["degree",0.0174532925199433],
        AUTHORITY["EPSG","4265"]],
    PROJECTION["Transverse_Mercator"],
    PARAMETER["latitude_of_origin",0],
    PARAMETER["central_meridian",9],
    PARAMETER["scale_factor",0.9996],
    PARAMETER["false_easting",1500000],
    PARAMETER["false_northing",0],
    UNIT["metre",1,
        AUTHORITY["EPSG","9001"]],
    AUTHORITY["EPSG","3003"]]
Origin = (1634712.000000000000000,4904391.000000000000000)
Pixel Size = (10.000000000000000,-10.000000000000000)
Metadata:
  AREA_OR_POINT=Area
Image Structure Metadata:
  COMPRESSION=DEFLATE
  INTERLEAVE=BAND
Corner Coordinates:
Upper Left  ( 1634712.000, 4904391.000) ( 10d41'17.17"E, 44d16'46.14"N)
Lower Left  ( 1634712.000, 4809821.000) ( 10d39'51.33"E, 43d25'42.21"N)
Upper Right ( 1723322.000, 4904391.000) ( 11d47'50.78"E, 44d15'27.69"N)
Lower Right ( 1723322.000, 4809821.000) ( 11d45'28.67"E, 43d24'26.04"N)
Center      ( 1679017.000, 4857106.000) ( 11d13'36.91"E, 43d50'40.36"N)
Band 1 Block=8861x1 Type=Float64, ColorInterp=Gray
  NoData Value=-99

giovanni

-- 
Giovanni Allegri
http://about.me/giovanniallegri
Twitter: https://twitter.com/_giohappy_
blog: http://blog.spaziogis.it
GEO+ geomatica in Italia http://bit.ly/GEOplus
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