[Libpqxx-general] Polygon data type in postgres

[Mark Gabriel Paylaga]

Corrections in the vertices reference from r[0][0] to r[1][0]....

On Mon, Jul 6, 2009 at 4:08 PM, Mark Gabriel Paylaga <mpaylaga at gmail.com>wrote:

> Hello all,
>
> I'm trying to retrieve the points of a polygon that are stored in the
> postgres db.
> The contents of the db are:
>  polygonid |
> vertices
>
> -----------+---------------------------------------------------------------------
>          2 |
> ((1,0),(1.5,-1),(2,-1),(2,1),(1,1),(0,0),(0,2),(3,2),(3,-2),(1,-2))
>          3 | ((3,3),(4,4))
>          4 | ((3,3),(4,4),(5,5))
>          5 | ((0,1))
>
> The vertices column is of type Polygon.
>
> I'm using libpqxx library for C++.
>
> Suppose I want to retrieve and access the points in the vertices column,
> I would execute these statements in C++:
>
>         result R = W.exec ("select * from polygon_tbl");
>         for (result::const_iterator r = R.begin();
>              r != R.end();
>              ++r)
>         {
>            int x = 0;
>            cout << "Polygon ID: " << r[0].to(x) << endl;
>
>            //Suppose i would like to print the first point of every
> polygon,
>            //how would i access it?
>            cout << "First vertex: " << r[1][0] << endl;    ???
>
>            //Or suppose i would like to print the first x coordinate of
> every polygon,
>            //how would i access it?
>            cout << "First x coordinate: " << r[1][0][0] << endl; ???? (am
> just guessing here..)
>
>         }
>
> Sorry I'm very new to libpqxx. I've pretty much understood how the libpqxx
> works but I'm stuck with the Polygon types. We actually just need a simple
> storage for our polygons in Postgres but I'm not sure how to access them
> using libpqxx.
>
> A little help would be nice... :)
>
> Best regards,
> Mark
>
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