Sunday, 24 December 2017

geometry - WKT: What is the reasoning behind the concept of a POINT EMPTY?


In data formats like WKT and WKB, we have ways of representing "empty" geometries. That all pretty much makes sense: a "LINESTRING EMPTY" is a LINESTRING type with 0 vertices. Same with a MULTIPOINT, POLYGON, etc.



But what about POINT EMPTY? For starters, there is no WKB representation for a POINT EMPTY, only WKT. GeoJSON also doesn't define this case in its specification.


According to the Wikipedia definition of a geometric point, "points do not have any length, area, volume, or any other dimensional attribute". So how can it be empty, and why does the WKT specification allow this?




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