[postgis-devel] Re: Binary Output Functions

[Paul Ramsey]

Here is what I did to try and enable this idea (I have not tested it 
with ArcMap yet). I did this for PostgreSQL 7.4. For version 8.0 the 
bytea() case would not be required:

create function geometrysend(geometry) returns bytea as 'select 
bytea(asbinary($1))' language sql;
update pg_type set typsend='geometrysend' where oid = (select oid from 
pg_type where typname = 'geometry');

Paul

Paul Ramsey wrote:

> Nevermind, with a little poking into the system catalogues, I found the 
> answer:
> 
> The "binary send format" is controlled by the "typsend" attribute in the 
> "pg_type" catalogue. So for example, for int4, the "typsend" is defined 
> as "int4send" and the C code is:
> 
> Datum
> int4send(PG_FUNCTION_ARGS)
> {
>         int32           arg1 = PG_GETARG_INT32(0);
>         StringInfoData buf;
> 
>         pq_begintypsend(&buf);
>         pq_sendint(&buf, arg1, sizeof(int32));
>         PG_RETURN_BYTEA_P(pq_endtypsend(&buf));
> }
> 
> So the return is a BYTEA. I am not sure what the right return type is 
> for geometry in this case to get interoperability with ESRI, whether it 
> is the OpenGIS WKB format or something else. Probably WKB. The user 
> could probably test this by simply updating the "geometry" entry in 
> pg_type and setting the typsend function to be "asbinary". This returns 
> (in postgis 1.0) a bytea in the OGC WKB format, which is (probably) what 
> ESRI is expecting.
> 
> Paul
> 
> 
>> Shachar,
>> You wrote (in response to a question about PgOleDB and PostGIS):
>>
>>
>> "OleDb, and accordingly, PgOleDb, is a binary interface driver. As such,
>> it gets all data types in binary form from the database. In order for a
>> datatype to be supported, two conditions must be satisfied:
>> 1. The data type must have a binary output function defined in PG itself.
>> 2. PgOleDb must know how to handle this type, to translate it to the
>> binary interface OLE DB is expected to return said type."
>>
>> Could you elabourate on item 1. above? What is the function signature 
>> that PgOleDB expects for the binary output function? It is a typecast 
>> to bytea? Something else? In a binary cursor, if you ask for a column, 
>> you should just get back the backend struct, which would then drop the 
>> system into your problem 2. above. And for that the guy you were 
>> talking to will actually need to start hacking in PgOleDb.  ESRI has 
>> some directions on doing spatial OLEDB, but the documentation is very 
>> very thin...
>>
>> http://arcgisdeveloperonline.esri.com/ArcGISDeveloper/ArcGISDevHelp/TechnicalDocuments/Geodatabase/Arc8_provider.htm 
>>
> 
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