GRASS Pixel Registration

Lee Graham lgraham at
Wed Aug 25 08:43:17 EDT 1993

The older versions of GRASS did seem to use the center pixel as reference
point, but the 4.0 programmer's manual points out that the reference is to
the outer edge instead (p. 25 - Chapter 5 Raster Maps).  To quote:
  Talking about the cellhd file...
        The geographic boundaries of the raster file are described by the
         north,south,east and west fields.  These values describe the lines
         which bound the map at its edges. BOLD - These lines do not pass
         through the center of the grid cells at the edge of the map, but
         along the edge of the map itself.
As for reporting of the values with d.what.rast, I'm not sure how it pivots
a position to report coordinates, but the center would make as much sense
as any other place.
   As far as we can tell, ARC/Info image files, grid, and GRASS files use the
edge of the cell for bounding coordinates and ERDAS uses the center.  

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