[gdal-dev] What decides zoom-levels

[Per Ohlson]

Hi,
I have two different geotiff-charts which have the same number of pixels, and similar information when viewing in gdalinfo,
but one misbehaves while tiling. 
For the problem chart, only the zoom levels 0-6 are tiled, but for the correctly handled chart, zoom levels 4-11 are tiled.
Both are around 23000x15000 pixels and 72 dpi.
So, what decides the zoom levels? I thought it was pixels and dpi..

gdalinfo on the working chart gives:

Coordinate System is:
Size is 15108, 23181
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 = (167.635052101782918,-27.435225354710909)
Pixel Size = (0.000619744987014,-0.000517525434692)
Metadata:
  AREA_OR_POINT=Area
Image Structure Metadata:
  COMPRESSION=LZW
  INTERLEAVE=PIXEL
Corner Coordinates:
Upper Left  ( 167.6350521, -27.4352254) (167d38' 6.19"E, 27d26' 6.81"S)
Lower Left  ( 167.6350521, -39.4319825) (167d38' 6.19"E, 39d25'55.14"S)
Upper Right ( 176.9981594, -27.4352254) (176d59'53.37"E, 27d26' 6.81"S)
Lower Right ( 176.9981594, -39.4319825) (176d59'53.37"E, 39d25'55.14"S)
Center      ( 172.3166057, -33.4336039) (172d18'59.78"E, 33d26' 0.97"S)
Band 1 Block=15108x1 Type=Byte, ColorInterp=Red
  Mask Flags: PER_DATASET ALPHA 
Band 2 Block=15108x1 Type=Byte, ColorInterp=Green
  Mask Flags: PER_DATASET ALPHA 
Band 3 Block=15108x1 Type=Byte, ColorInterp=Blue
  Mask Flags: PER_DATASET ALPHA 
Band 4 Block=15108x1 Type=Byte, ColorInterp=Alpha

gdalinfo on the problem chart gives:
Size is 15319, 23593
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 = (176.502369113268770,-25.635284667174400)
Pixel Size = (0.000619910224237,-0.000526829594898)
Metadata:
  AREA_OR_POINT=Area
Image Structure Metadata:
  COMPRESSION=LZW
  INTERLEAVE=PIXEL
Corner Coordinates:
Upper Left  ( 176.5023691, -25.6352847) (176d30' 8.53"E, 25d38' 7.02"S)
Lower Left  ( 176.5023691, -38.0647753) (176d30' 8.53"E, 38d 3'53.19"S)
Upper Right (     185.999,     -25.635) (185d59'55.59"E, 25d38' 7.02"S)
Lower Right (     185.999,     -38.065) (185d59'55.59"E, 38d 3'53.19"S)
Center      (     181.251,     -31.850) (181d15' 2.06"E, 31d51' 0.11"S)
Band 1 Block=15319x1 Type=Byte, ColorInterp=Red
  Mask Flags: PER_DATASET ALPHA 
Band 2 Block=15319x1 Type=Byte, ColorInterp=Green
  Mask Flags: PER_DATASET ALPHA 
Band 3 Block=15319x1 Type=Byte, ColorInterp=Blue
  Mask Flags: PER_DATASET ALPHA 
Band 4 Block=15319x1 Type=Byte, ColorInterp=Alpha

Regards
/Per



Per Ohlson, M.Sc. E.E.
Nanight AB - http://www.nanight.se
Stockholm/Gothenburg, Sweden
per.ohlson at nanight-tech.com

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