[postgis-devel] [WKT Raster] Plan to add ST_AsBinary

[Mateusz Loskot]

Mark Cave-Ayland wrote:
> Mateusz Loskot wrote:
>> 
>> What I'm looking for is what's the difference between ST_AsBinary 
>> and ST_bytea, in PostGIS. Both functions are based on 
>> WKBFromLWGEOM, so I assume they return object of exactly the same 
>> type. AFAIU, the difference is that ST_AsBinary enables users to 
>> choose endianness of output binary. Am I right? Is that all or 
>> something is missing?
> 
> IIRC the original PostGIS binary send/receive functions used HEXEWKB
>  rather than bytea which is probably why the ST_bytea function is 
> there (in fact, I didn't really notice it was there until you 
> mentioned it!). So in short, ST_bytea is deprecated and really 
> shouldn't be used - just stick with the ST_AsBinary()-type API and I 
> don't think you can go far wrong.

I understand ST_bytea is deprecated, but it doesn't change the fact
that, AFAI can read the code, it returns WKB in the same form (bytea
object) as ST_AsBinary does.

Internally, both functions use WKBFromLWGEOM() and this function
forwards the job to serialized_lwgeom_to_ewkb().
The only (significant) difference I can see is that using ST_AsBinary
I can control endianness of output, but ST_bytea always returns
it as big-endian (network byte order) which is native for PostgreSQL
in binary games.

To summary,:
* existence of ST_bytea does not hurt
* semantic of ST_AsBinary is the same with extra options

Am I correct? If I am, I'd like to follow the same pattern making
ST_AsBinary for WKT Raster.

Best regards,
-- 
Mateusz Loskot, http://mateusz.loskot.net