[gdal-dev] Downsample with averaging?

[Jay Jennings]

Unfortunately I can’t provide the file (it’s about 2.1 GB and not releasable), but below is the ‘gdalinfo’ dump for it.

The problem may be related to size of the input, because the same command worked OK on a GeoTiff that is “only” 975 MB.

BTW   For the 975 GB run that succeeded, the created overview was named *.ovr rather than *.tif.   Is this expected ?   The guidance for ‘gdaladdo’ hints that the created *.ovr is actually a TIFF, but that’s not true here (I tried renaming it *.tif, but no TIFF reader could open it).


Driver: GTiff/GeoTIFF
Files: XXXXXX.tif
Size is 25733, 27840
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 = (-100.375165330488004,29.624901844319002)
Pixel Size = (0.000004869286704,-0.000004495684143)
Metadata:
  TIFFTAG_DATETIME=2009:07:17 06:16:07
  TIFFTAG_ARTIST=GeoEye
  TIFFTAG_COPYRIGHT=(C) COPYRIGHT GeoEye, All Rights Reserved
  TIFFTAG_MINSAMPLEVALUE=0
  TIFFTAG_MAXSAMPLEVALUE=255
  AREA_OR_POINT=Area
Image Structure Metadata:
  INTERLEAVE=PIXEL
Corner Coordinates:
Upper Left  (  -100.3751653,  29.6249018) ( 100d22'30.60"W, 29d37'29.65"N)
Lower Left  (  -100.3751653,  29.4997420) ( 100d22'30.60"W, 29d29'59.07"N)
Upper Right (  -100.2498639,  29.6249018) ( 100d14'59.51"W, 29d37'29.65"N)
Lower Right (  -100.2498639,  29.4997420) ( 100d14'59.51"W, 29d29'59.07"N)
Center      (  -100.3125146,  29.5623219) ( 100d18'45.05"W, 29d33'44.36"N)
Band 1 Block=512x512 Type=Byte, ColorInterp=Red
Band 2 Block=512x512 Type=Byte, ColorInterp=Green
Band 3 Block=512x512 Type=Byte, ColorInterp=Blue

From: Chaitanya kumar CH [mailto:chaitanya.ch at gmail.com]
Sent: Monday, February 21, 2011 4:19 PM
To: Jay Jennings
Cc: gdal-dev at lists.osgeo.org
Subject: Re: [gdal-dev] Downsample with averaging?

Jay,

Can you provide a sample file that gives this error?
On Tue, Feb 22, 2011 at 1:56 AM, Jay Jennings <Jennings.Jay at geoeye.com<mailto:Jennings.Jay at geoeye.com>> wrote:
Hello list,
(using GDAL 1.8.0) I am trying to create a 32:1 down-sampled overview of a GeoTiff satellite image.  My first thought was gdal_translate, with args such as “-outsize 3.125% 3.125%”… which produces surprisingly high quality given the absence of a resampling option.   However I’m looking for a downsampling scheme that creates a result pixel by averaging all relevant source pixels (I know, for 32:1 downsample, that means 1024 source pixels for each result pixel !) with the hope of an output that is not “speckled” or “grainy” insofar as possible.

I also looked at gdaladdo, which does have the “-r average” resampling option… the guidance at gdal.org<http://gdal.org> seems to suggest that it can produce a 32:1 GeoTIFF external overview with a command like this:

gdaladdo  -r  average  -ro  XXXXX.tif  32

But that produces a surprising error message, namely:
ERROR 4: `XXXXX.tif.ovr' does not exist in the file system, and is not recognised as a supported dataset name.

Am I barking up the wrong tree with gdaladdo for this purpose ?  Anybody have any suggestions for highest-quality down-sampling ? Thanks in advance.

--Jay Jennings

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--
Best regards,
Chaitanya kumar CH.
/tʃaɪθənjə/ /kʊmɑr/
+91-9494447584
17.2416N 80.1426E
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