[postgis-devel] Can I call LWGEOM_x_point directly from another stored procedure?

[Paul Ramsey]

Ah, if you don't have postgis headers to compile against you're not going to be able to pass DirectFunctionCall something it understands. 
What I did for pointcloud was, for the functions I needed to interop with PostGIS, emitted and consumed WKB in postgresql bytea format. Then I could pass that to geomfromwkb and that to whatever, and do it all in SQL wrappers. 

The SQL wrappers would have a dependency on the existence of the 'geometry' type in the system catalogs, but the actual code has no compile-time (or even run-time) dependency on postgis code. 

You can see how it works sort of in the the pointcloud repo and the pgsql_postgis directory

P. 

-- 
Paul Ramsey
http://cleverelephant.ca
http://postgis.net


On Sunday, November 17, 2013 at 8:21 AM, Stephen Woodbridge wrote:

> Hi Paul,
> 
> Thanks for that pointer.
> 
> So below is what I came up with (uncompiled and untested), but I have a 
> few questions. Since this code is in another extension (ie: NOT PostGIS) 
> I can not access PostGIS utility functions or headers. Questions:
> 
> 1. Is the external function references below the correct way to define 
> these so DirectFunctionCalls can reference those entry points or do I 
> need to throw an external in front of them?
> 
> 2. I mimiced the array access code in LWGEOM_makeline_garray but don't 
> want to use GSERIALIZED *. Is the pointer returned from ARR_DATA_PTR() a 
> pointer to a Datum? And is this the correct way to work with this:
> Datum geom = PointerGetDatum(ARR_DATA_PTR(pnts)+offset);
> or should I use:
> Datum geom = ARR_DATA_PTR(pnts)+offset;
> or something else all together? All I need is a Datum that I can pass 
> into DirectFunctionCalln().
> 
> I would appreciate it is someone could code review this and correct me 
> if I have it wrong.
> 
> By the way, this is for code that will be wrapping OSRM server into 
> plpgsql functions as part of pgRouting or OSRM project. In essence, you 
> will be able to pass an array of points to a function and get back the 
> OSRM route geometry or a distance matrix. I'll also have to figure out 
> how to construct a polyline object and return that in a similar way.
> 
> Thanks,
> -Steve
> 
> /* external function references */
> Datum LWGEOM_makeline_garray(PG_FUNCTION_ARGS);
> Datum LWGEOM_x_point(PG_FUNCTION_ARGS);
> Datum LWGEOM_y_point(PG_FUNCTION_ARGS);
> 
> static void deconstruct_point(Datum datum, float8 *x, float8 *y, int *srid)
> {
> *x = DatumGetFloat8(DirectFunctionCall1(LWGEOM_x_point, datum);
> *y = DatumGetFloat8(DirectFunctionCall1(LWGEOM_y_point, datum);
> *srid = DatumGetInt32(DirectFunctionCall1(LWGEOM_get_srid, datum);
> }
> 
> And that would be getting called from something like:
> 
> int nelems;
> int len;
> bits8 *bitmap;
> int bitmask;
> size_t offset;
> 
> Datum datum = PG_GETARG_DATUM(0);
> ArrayType pnts = DatumGetArrayTypeP(datum);
> nelems = ArrayGetNItems(ARR_NDIM(pnts), ARR_DIMS(pnts));
> 
> bitmap = ARR_NULLBITMAP(pnts);
> bitmask = 1;
> offset = 0;
> for (i=0; i<nelems; i++) {
> /* Don't do anything for NULL values */
> if ((bitmap && (*bitmap & bitmask) != 0) || !bitmap) {
> Datum geom = PointerGetDatum(ARR_DATA_PTR(pnts)+offset);
> offset += INTALIGN(VARSIZE(geom));
> deconstruct_point(geom, &x, &y, &srid);
> // work with x, y, srid
> }
> /* Advance NULL bitmap */
> if (bitmap) {
> bitmask <<= 1;
> if (bitmask == 0x100) {
> bitmap++;
> bitmask = 1;
> }
> }
> }
> 
> 
> On 11/16/2013 11:44 PM, Paul Ramsey wrote:
> > Have you checked out the DirectFuctionCall PgSQL macros? Might do what you want.
> > 
> > 
> > On Saturday, November 16, 2013 at 8:39 PM, Stephen Woodbridge wrote:
> > > Hi strk,
> > > 
> > > I would like to be able to pass a PostGIS point or point[] to a
> > > pgRouting function and I'm wondering if is it is possible to directly
> > > call LWGEOM_x_point() and somehow pass on of my args to that?
> > > 
> > > Basically, I would like a simple way to get x, y, and srid from a point.
> > > I guess I can clone the code from LWGEOM_x_point into a function to
> > > extract those.
> > > 
> > > Do I need to do anything to initialize stuff for postgis in my function?
> 
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