[postgis-devel] Question about Postgis serialisation to postgresql varlena

[Sandro Santilli]

On Wed, Aug 26, 2015 at 10:27:25AM +0200, Karel Maesen wrote:
> Hi list,
> 
> I’m the lead developer of Hibernate Spatial. Hibernate Spatial adds support for spatial types and operations to the Hibernate Object-Relation Mapping, which is very popular in the Java world. 
> 
> Recently I started using my own code to perform the deserialisation from Postgis Geometry to Java objects. As reference I used the description in the source file ./postgis/SERIALIZED_FORM and https://trac.osgeo.org/postgis/wiki/DevWikiPostGISCoding. I was under the impression that, at least from version 1.0 of Postgis, this file documents the internal varlena serialisation format of the Geometry type. 
> 
> Now I have received a bug report saying that the deserialization of a geometry failed. Apparently the Geometry returned from the database is encoded in an EWKT text value, not the binary object described in SERIALIZED_FORM.  
>
> Is it possible that a Postgis 1.5.2 database contains geometries serialized as EWKT text? Could any of the Postgis developers confirm that the format in SERIALIZED_FORM is the only format possible?

The object is stored in the database with a theoretically opaque
format, and it gets transformed to a "canonical" format when retrived.

PostgreSQL accounts for two "canonical" forms: binary and text.
Which one is used depends on the cursor you use for fetching the data
(binary or text).

The canonical text output is HEXEWKT, the canonical binary output is EWKB.
This hasn't changed between 1.5 and 2.0.

--strk; 

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