9.34.3.Precision of Geometries

The internal precision of geometry operations is 64 bit IEEE floating point. Normally, a geometry index for geography uses can be made with 32 bit floats for space efficiency, as these still give a precision of about 2 meters on the surface of the Earth. A geometry object is stored with all coordinates either as float or double depending on which data type was supplied in creating the object. Note that the object itself can have more precise coordinates than the representation of its bounding box in the R tree index.

Bounding boxes for shapes can be calculated approximately as soon as shape contain any arcs. In any case, bounding box of a shape is a bit bigger than the shape itself in order to tolerate rounding errors. Predicates for spatial relations accept an additional, non-standard, argument for tolerance. If the tolerance is greater than zero, borders of shapes are treated as wide lines with thickness is approximately equal to the specified tolerance. That is useful for dealing with inaccurate data such as amateur GPS/GLONASS tracks, coordinates rounded to minutes when published in Dbpedia and the like.