Changes between Version 2 and Version 3 of rfc33_gtiff_pixelispoint
- Timestamp:
- Nov 15, 2010, 11:47:31 AM (13 years ago)
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rfc33_gtiff_pixelispoint
v2 v3 11 11 == Rationale == 12 12 13 The GeoTIFF specification includes a data item, GTRasterTypeGeoKey, which may be set to either RasterPixelIsArea (the default), or RasterPixelIsPoint. RasterPixelIsArea defines that a pixel represents an area in the real world, whileRasterPixelIsArea defines a pixel to represent a point in the real world. Often this is useful to distinguish the behavior of optical sensors that average light values over an area vs. raster data which is point oriented like an elevation sample at a point.13 The GeoTIFF specification includes a data item, GTRasterTypeGeoKey, which may be set to either !RasterPixelIsArea (the default), or !RasterPixelIsPoint. !RasterPixelIsArea defines that a pixel represents an area in the real world, while !RasterPixelIsArea defines a pixel to represent a point in the real world. Often this is useful to distinguish the behavior of optical sensors that average light values over an area vs. raster data which is point oriented like an elevation sample at a point. 14 14 15 Traditionally GDAL has treated this flag as having no relevance to the georeferencing of the image despite disputes from a variety of other software developers and data producers. This was based on the authors interpretation of something said once by the GeoTIFF author. However, a recent review of section <a href="http://www.remotesensing.org/geotiff/spec/geotiff2.5.html#2.5.2.2">section 2.5.2.2</a> of the GeoTIFF specificaiton has made it clear that GDAL behavior is incorrect and thatPixelIsPoint georeferencing needs to be offset by a half a pixel when transformed to the GDAL georeferencing model. This issue is documented in the following tickets including #3837, #3838, ....15 Traditionally GDAL has treated this flag as having no relevance to the georeferencing of the image despite disputes from a variety of other software developers and data producers. This was based on the authors interpretation of something said once by the GeoTIFF author. However, a recent review of section [[http://www.remotesensing.org/geotiff/spec/geotiff2.5.html#2.5.2.2 section 2.5.2.2]] of the GeoTIFF specificaiton has made it clear that GDAL behavior is incorrect and that !PixelIsPoint georeferencing needs to be offset by a half a pixel when transformed to the GDAL georeferencing model. This issue is documented in the following tickets including #3837, #3838, .... 16 16 17 17 This RFC attempts to manage this transition with a minimum of disruption for the users of GDAL/OGR.
