[gdal-dev] gdal2tiles: tiles in wrong hemisphere,
and/or Openlayers problem
geep999
geep999 at yahoo.co.uk
Thu Nov 10 15:58:01 EST 2011
Hi,
I'm having big problems understanding what's happening with tiles created
by gdal2tiles.py --version GDAL 1.8.1, released 2011/07/09
Running on Slackware 13.37 64 bit.
The results of tiling a colour relief look OK:
http://pgg999.freehostingcloud.com/tiles4_srtm/openlayers.html
http://pgg999.freehostingcloud.com/tiles4_srtm/openlayers.html
(The file openlayers.html was also created by gdal2tiles.py)
But I can't understand the naming of the tiles created by gdal2tiles.py.
For example - consider a couple of tiles created by other folk for Harlow,
Essex,UK at zoom 11
http://tile.openstreetmap.org/11/1024/678.png
http://tile.openstreetmap.org/11/1024/678.png
http://steve8.dev.openstreetmap.org/railway_tiles/11/1024/678.png
http://steve8.dev.openstreetmap.org/railway_tiles/11/1024/678.png
For these I can understand the z/x/y of 11/1024/678
and http://almien.co.uk/OSM/Tools/Coord/?x=1024&y=678&z=11
gives:
Latitude: 51.726959 to 51.835708 Longitude: 0.000000 to 0.175781
Size: 0.175781 x 0.108749 Centre: 51.781333, 0.087891
But my gdal2tiles.py has named the same area 11/1024/1369
http://pgg999.freehostingcloud.com/tiles4_srtm/11/1024/1369.png
http://pgg999.freehostingcloud.com/tiles4_srtm/11/1024/1369.png
I attach, below at the bottom, the gdal2tiles.py command I used and details
of the source geotiff image.
For z/x/y of 11/1024/1369
http://almien.co.uk/OSM/Tools/Coord/?x=1024&y=1369&z=11
http://almien.co.uk/OSM/Tools/Coord/?x=1024&y=1369&z=11
gives:
Latitude: -51.835708 to -51.726959 Longitude: 0.000000 to 0.175781
Size: 0.175781 x 0.108749 Centre: -51.781333, 0.087891
Seems the tile is being created in the southern hemisphere in the South
Atlantic.
The geotiff image used to create the tiles is definitely in the Northen
Hemisphere - Eastern England.
Yet as you can see everything looks OK in
http://pgg999.freehostingcloud.com/tiles4_srtm/openlayers.html
I created a stripped down version of the tile pyramid that only contains one
tile.
http://pgg999.freehostingcloud.com/tiles4_srtm_1tile/openlayers.zoom11.html
http://pgg999.freehostingcloud.com/tiles4_srtm_1tile/openlayers.zoom11.html
http://pgg999.freehostingcloud.com/tiles4_srtm_1tile/11/1024/1369.png
http://pgg999.freehostingcloud.com/tiles4_srtm_1tile/11/1024/1369.png
/Can anybody help me to understand:
1/ Why is gdalstiles.py apparently creating tiles in the Southern Hemisphere
which should be in the Northern?
Specificially - 11/1024/1369.png should be 11/1024/678.png
2/ Why is a tile that, according to its name, should be displayed in the
South Atlantic appearing in Essex, England?
Or should I ask this question to the Openlayers folks?/
This is causing me lots of problems when I try to use my tiles along with
other tiles.
Then my tiles are appearing in the "wrong" place - i.e. the Southern
Atlantic.
I don't have a presentable example of this yet. It's taken me long enough to
get this far!
At the moment I'm wondering if there are bugs in both gdal2tiles.py and
http://www.openlayers.org/api/2.7/OpenLayers.js
http://www.openlayers.org/api/2.7/OpenLayers.js
Cheers,
Peter
Command used to create tile:
gdal2tiles.py --zoom=0-14
--url=http://pgg999.freehostingcloud.com/tiles_srtm/ \
-v N5xE000.srtm.colourrelief.tif tiles4_srtm
Details of the colour relief file that was tiled.
(It is actually 9 SRTM tiles stitched together with gdal_merge.py).
gdalinfo -stats
/media/space5/ordnance_survey_data/bdline_gb/data/N5xE000.srtm.colourrelief.tif
Driver: GTiff/GeoTIFF
Files:
/media/space5/ordnance_survey_data/bdline_gb/data/N5xE000.srtm.colourrelief.tif
/media/space5/ordnance_survey_data/bdline_gb/data/N5xE000.srtm.colourrelief.tif.aux.xml
Size is 3601, 3601
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 = (-1.000416666666667,53.000416666666666)
Pixel Size = (0.000833333333333,-0.000833333333333)
Metadata:
AREA_OR_POINT=Area
Image Structure Metadata:
INTERLEAVE=PIXEL
Corner Coordinates:
Upper Left ( -1.0004167, 53.0004167) ( 1d 0' 1.50"W, 53d 0' 1.50"N)
Lower Left ( -1.0004167, 49.9995833) ( 1d 0' 1.50"W, 49d59'58.50"N)
Upper Right ( 2.0004167, 53.0004167) ( 2d 0' 1.50"E, 53d 0' 1.50"N)
Lower Right ( 2.0004167, 49.9995833) ( 2d 0' 1.50"E, 49d59'58.50"N)
Center ( 0.5000000, 51.5000000) ( 0d30' 0.00"E, 51d30' 0.00"N)
Band 1 Block=3601x1 Type=Byte, ColorInterp=Red
Min=46.000 Max=251.000
Minimum=46.000, Maximum=251.000, Mean=111.271, StdDev=75.256
Metadata:
STATISTICS_MINIMUM=46
STATISTICS_MAXIMUM=251
STATISTICS_MEAN=111.2714725406
STATISTICS_STDDEV=75.256273643809
Band 2 Block=3601x1 Type=Byte, ColorInterp=Green
Min=55.000 Max=255.000
Minimum=55.000, Maximum=255.000, Mean=175.914, StdDev=36.022
Metadata:
STATISTICS_MINIMUM=55
STATISTICS_MAXIMUM=255
STATISTICS_MEAN=175.91388581082
STATISTICS_STDDEV=36.021876564052
Band 3 Block=3601x1 Type=Byte, ColorInterp=Blue
Min=31.000 Max=238.000
Minimum=31.000, Maximum=238.000, Mean=94.943, StdDev=16.832
Metadata:
STATISTICS_MINIMUM=31
STATISTICS_MAXIMUM=238
STATISTICS_MEAN=94.942947441009
STATISTICS_STDDEV=16.832038042577
--
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