Changes between Version 50 and Version 51 of NetCDF_exportUpdateChanges


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Timestamp:
Oct 18, 2011, 12:41:51 PM (13 years ago)
Author:
etourigny
Comment:

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  • NetCDF_exportUpdateChanges

    v50 v51  
    139139 * and individual corner coordinates (NN, SS, WE and WW).
    140140
    141 The new implementation does not save the GeoTransform array, with the exception of when the GeoTransform cannot be retrieved from the netcdf file (i.e. only for a geographic CRS, in the specific case that lon/lat values are not written ). This has the effect that in some cases, the computed pixel width and height (GT(1) and GT(5)) differs by a very small amount from the original values in the GDAL raster file, due to various floating-point operations and half-pixel shifts.
    142 
    143 For example,
    144 {{{
    145 Given a landsat file (tmp/melb-small_AEA.nc) generated by the autotest netcdf_cdf_4:
    146 
    147 src:(1232736.8666076646, 30.080459243369152, 0.0, -4118493.9582119514, 0.0, -30.080459243369152)
    148 dst:(1232736.8666076646, 30.080459243369834, 0.0, -4118493.9582119514, 0.0, -30.080459243366494)
    149 
    150 The difference in width/height is less than 10E^-11 (10 pm), while the corners are identical.
    151 
    152 However, when translating the original landsat file (melb-small.tif) in UTM, the pixel width/height of 30m is preserved exactly.
    153 }}}
    154 
    155 We feel that this difference is marginal, however should a strong argument be presented, we could save the GeoTransform as before and compare with the values stored in the CF dimensions variable for conflict.
     141The new implementation does not save the GeoTransform array, with the exception of when the GeoTransform cannot be retrieved from the netcdf file (i.e. only for a geographic CRS, in the specific case that lon/lat values are not written ).
     142
     143This has the effect that in some cases, the computed pixel width and height (GT(1) and GT(5)) differs by a very small amount (e.g. for 30m pixels, <10^11, the order or a picometer) from the original values in the GDAL raster file, due to various floating-point operations and half-pixel shifts. We feel that this difference is marginal, however should a strong argument be presented, we could save the GeoTransform as before and compare with the values stored in the CF dimensions variable for conflict.
     144
    156145The corner coordinates are never saved as they are redundant. When importing a CF file, if GeoTransform cannot be computed from dimension variables, GeoTransform and corner coordinates are consulted if available.
    157146