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?

• Why whould a line with zero vertices make sense, while a point with no vertices doesn't? They're all really nil geometries, special cases so that dimensionality can be preserved in a column which is restricted to a single datatype. – Vince Aug 8 '14 at 11:50
• It doesn't make sense because POINTs are the primitive of all the other geometries. The other geometries are just collections of POINTs with some specific semantics. Geometrically speaking, a NULL geometry doesn't really make sense. But within a standard like WKB, it's allowed. The problem is, there is no way to represent a POINT EMPTY in WKB. This is a problem if you try to convert between different data formats. WKT and WKB are used very closely together, but there's an inconsistency. – larsbutler Aug 11 '14 at 9:12
• An Empty Point has as much significance and use, as the number Zero. – Devdatta Tengshe Aug 11 '14 at 11:39
• Which makes this the same question you asked last time. A point isn't a primitive, it's the most common type of data. The lack of an empty point in WKB is a flaw in WKB, not in the point type. – Vince Aug 11 '14 at 11:45

• I do not know if such answer exists. Missing POINT EMPTY in WKB can perhaps be considered as a bug but accepted standards do not change so easily. However, the OGC GeoPackage standard considers this case geopackage.org/spec `Well-Known Binary as defined in ISO 13249-3 [12] does not provide a standardized encoding for an empty point set (i.e., Point Empty in Well-Known Text). In GeoPackages these points SHALL be encoded as a Point where each coordinate value is set to an IEEE-754 quiet NaN value. ` – user30184 Aug 11 '14 at 9:28