[postgis-users] PostGIS and LIDAR Massive Point Sets

[Paul Ramsey]

David Blasby wrote:

> The WKB representation for a 2d point has 5 bytes of overhead (endian 
> flag and a 4-byte type tag) for a total of 21 bytes.  WKB of a 3d point 
> also has 5 bytes of overhead, for a total of 29 bytes.  Postgresql has a 
> further 4 bytes of overhead.

You know, one of the reasons WKB (and PostGIS internals) structures 
carry extra overhead is because they are general structures -- all 
geometry types are represented with the same structure. Which is kind of 
wasteful when you think that PostgreSQL itself is also taking overhead 
to describe the object type.  If we actually had the full 7 geometry 
types in PostgreSQL as full fledged types we could have the optimal 
storage for each (why store a bounding box for a point? it's a 
*point*!). The main argument against this is a code maintenance one -- 
index bindings for each type, instead for just one.

It is a hard call, since the only reasons to do this kind of reworking 
are potential performance increases, and we have no quantification of 
performance gains to expect. The only thing we *do* know for sure is 
that this kind of optimization would save some disk space.

P.

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      | Paul Ramsey
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