Pixel-Is-Point or Pixel-Is-Area

The GeoTIFF specification includes a data item, GTRasterTypeGeoKey (#1025), which may be set to either RasterPixelIsArea (maybe the default, but not clear in 7.2.1), or RasterPixelIsPoint.

 RasterPixelIsArea defines that a pixel represents an area in the real world, while RasterPixelIsPoint 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.

This is a real world issue with Key Global Regional DEMs.  For these, some follow the

In "Arc-speak" these are



View of the grid for a 1" geographic grid in Alaska, where the spacing is about 15 m x 30 m.  The black star represents the geographic position of a pixel.

A number of programs (e.g. GDAL, GRASS) turn all DEMs into Pixel-Is-Area, transforming all coordinates by a half pixel.

References:

Much older references


Last revision 5/29/2022