[gdal-dev] What decides zoom-levels

[Even Rouault]

Le lundi 21 janvier 2013 20:15:42, Per Ohlson a écrit :
> 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..

You probably don't give the whole context. From the gdalinfo output, I can 
tell that none of your geotiffs are tiled, or have overviews (precomputed zoom 
levels). So this may depend on the application that make use of them.

> 
> 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