Low accuracy when using Geotiff and WCS.
----------------------------------------
Key: GEOS-4372
URL: http://jira.codehaus.org/browse/GEOS-4372
Project: GeoServer
Issue Type: Bug
Components: WCS
Affects Versions: 2.0.2
Environment: Ubuntu 10.04, Amazon EC2 Small Instance
Reporter: Ariel Núñez
Assignee: Andrea Aime
Priority: Minor
Attachments: downloaded.tif, original.tif
While writing unit tests for a scientific application using GeoServer we
noticed that it is not possible to obtain a faithful copy of the original when
uploading a geotiff and then requesting it via WCS.
To be specific we have observed that when uploading and downloading a raster
dataset to GeoServer the following is changed:
The bounding box by something in the order of 10%
The number of rows and columns of the array (i.e. the shape) by +/- 1. This
means that the original array cannot be compared directly to the downloaded
array as they are not aligned.
The origin and pixel size by a few % (This means that the georeferencing of the
grid is changed)
The grid values themselves are also not exact showing some quite large spikes
in some places although viewing the TIF files (before and after passing through
GeoServer) shows that they are overall qualitatively similar.
The bottom line is that while the accuracy of data served by GeoServer is
adequate for viewing it is most likely not sufficient for analysis or
calculations
GET
/geoserver/wcs?version=1.0.0&service=wcs&request=getcoverage&identifier=original&format=GeoTIFF&BoundingBox=-5.519000,96.956000,2.289000,104.641000,urn:ogc:def:crs:EPSG::4326&store=false&coverage=original&crs=EPSG:4326&bbox=96.956000,-5.519000,104.641000,2.289000&resx=0.030741064&resy=0.030741064
$ gdalinfo original.tif
Driver: GTiff/GeoTIFF
Files: original.tif
Size is 250, 254
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 = (96.956000000000003,2.289497256000100)
Pixel Size = (0.030741064000000,-0.030741064000000)
Metadata:
AREA_OR_POINT=Area
Image Structure Metadata:
INTERLEAVE=BAND
Corner Coordinates:
Upper Left ( 96.9560000, 2.2894973) ( 96d57'21.60"E, 2d17'22.19"N)
Lower Left ( 96.9560000, -5.5187330) ( 96d57'21.60"E, 5d31'7.44"S)
Upper Right ( 104.6412660, 2.2894973) (104d38'28.56"E, 2d17'22.19"N)
Lower Right ( 104.6412660, -5.5187330) (104d38'28.56"E, 5d31'7.44"S)
Center ( 100.7986330, -1.6146179) (100d47'55.08"E, 1d36'52.62"S)
Band 1 Block=250x4 Type=Float64, ColorInterp=Gray
$ gdalinfo downloaded.tif
Driver: GTiff/GeoTIFF
Files: downloaded.tif
Size is 249, 253
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 = (96.971431726907639,2.273569169960474)
Pixel Size = (0.030863453815261,-0.030861660079051)
Metadata:
TIFFTAG_XRESOLUTION=1
TIFFTAG_YRESOLUTION=1
TIFFTAG_RESOLUTIONUNIT=1 (unitless)
AREA_OR_POINT=Point
Image Structure Metadata:
COMPRESSION=LZW
INTERLEAVE=BAND
Corner Coordinates:
Upper Left ( 96.9714317, 2.2735692) ( 96d58'17.15"E, 2d16'24.85"N)
Lower Left ( 96.9714317, -5.5344308) ( 96d58'17.15"E, 5d32'3.95"S)
Upper Right ( 104.6564317, 2.2735692) (104d39'23.15"E, 2d16'24.85"N)
Lower Right ( 104.6564317, -5.5344308) (104d39'23.15"E, 5d32'3.95"S)
Center ( 100.8139317, -1.6304308) (100d48'50.15"E, 1d37'49.55"S)
Band 1 Block=256x256 Type=Float64, ColorInterp=Gray
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