Add Support For EWKT

[hendursaga]

Extended WKT is a simple variant used in PostGIS and related software, in particular, the SRID. Presently trying to parse something like SRID=4326; throws InvalidWKT("Invalid type encountered") as the error.

It appears there already is an issue opened for the up to 4 ordinate values part of the spec.

The BNF spec provided by PostGIS would be a helpful guide.

[zdannar]

• 1

[urschrei]

As ever, @zdannar and @hendursaga, we're severely time-constrained so this is extremely unlikely to get done in the foreseeable future. If you have a requirement for it, we're happy to talk through it with a view to accepting a PR.

[zdannar]

After looking into it more, I am not sure it makes sense to include it into this code base. From what I have read, EWKT is a postgres specific format meaning that it probably should not exist in this domain.