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Post GIS extended formats are currently superset of OGC one (every valid WKB/WKT is a valid EWKB/EWKT) but this might vary in the future, specifically if OGC comes out with a new format conflicting with our extensions. Post GIS EWKB/EWKT add 3dm,3dz,4d coordinates support and embedded SRID information.Examples of the text representations (EWKT) of the extended spatial objects of the features are as follows.Examples of some simple curved geometries are shown below: The geography type provides native support for spatial features represented on "geographic" coordinates (sometimes called "geodetic" coordinates, or "lat/lon", or "lon/lat").
For the postgis 'geometry' type these are: The SQL Multimedia Applications Spatial specification extends the simple features for SQL spec by defining a number of circularly interpolated curves.
Post GIS extends the standard with support for 3DZ,3DM and 4D coordinates.
The Open GIS specification defines two standard ways of expressing spatial objects: the Well-Known Text (WKT) form and the Well-Known Binary (WKB) form.
For more accurate measurements, the calculations must take the actual spheroidal shape of the world into account, and the mathematics becomes very complicated indeed.
Because the underlying mathematics is much more complicated, there are fewer functions defined for the geography type than for the geometry type.
That means calculations on geometries (areas, distances, lengths, intersections, etc) can be calculated using cartesian mathematics and straight line vectors.