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<h1>x03_d_soci_example.cpp</h1>Example showing how to get polygons from PostGIS using SOCI and use them in GGL through WKB<p>
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<div class="fragment"><pre class="fragment"><span class="comment">// Boost.Geometry (aka GGL, Generic Geometry Library)</span>
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<span class="comment">//</span>
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<span class="comment">// Copyright Mateusz Loskot 2009, mateusz@loskot.net</span>
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<span class="comment">//</span>
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<span class="comment">// Use, modification and distribution is subject to the Boost Software License,</span>
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<span class="comment">// Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at</span>
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<span class="comment">// http://www.boost.org/LICENSE_1_0.txt)</span>
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<span class="comment">// Boost.Geometry (aka GGL, Generic Geometry Library)</span>
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<span class="comment">// SOCI example</span>
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<span class="comment">// d: using WKB to retrieve geometries</span>
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<span class="comment">// SOCI is a generic C++ template interface to access relational databases</span>
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<span class="comment">// To build and run this example, see comments in example a</span>
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<span class="comment">// Alternatively compile composing and executing compiler command directoy in examples directory,</span>
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<span class="comment">// for example using GCC compiler:</span>
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<span class="comment">// g++ -I../../../boost -I/home/mloskot/usr/include/soci \</span>
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<span class="comment">// -I /home/mloskot/usr/include/soci/postgresql -I/usr/include/postgresql \</span>
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<span class="comment">// -L/home/mloskot/usr/lib -lsoci_core-gcc-3_0 -lsoci_postgresql-gcc-3_0 x03_c_soci_example.cpp</span>
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<span class="preprocessor">#include <soci.h></span>
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<span class="preprocessor">#include <soci-postgresql.h></span>
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<span class="preprocessor">#include <exception></span>
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<span class="preprocessor">#include <iostream></span>
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<span class="preprocessor">#include <iterator></span>
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<span class="preprocessor">#include <string></span>
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<span class="preprocessor">#include <vector></span>
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<span class="preprocessor">#include <boost/geometry/geometry.hpp></span>
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<span class="preprocessor">#include <<a class="code" href="algorithms_2area_8hpp.html">boost/geometry/algorithms/area.hpp</a>></span>
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<span class="preprocessor">#include <<a class="code" href="cartesian2d_8hpp.html">boost/geometry/geometries/cartesian2d.hpp</a>></span>
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<span class="preprocessor">#include <<a class="code" href="geometries_8hpp.html">boost/geometry/geometries/geometries.hpp</a>></span>
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<span class="preprocessor">#include <boost/geometry/extensions/gis/io/wkb/read_wkb.hpp></span>
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<span class="preprocessor">#include <boost/geometry/extensions/gis/io/wkb/utility.hpp></span>
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<span class="preprocessor">#include <boost/geometry/extensions/gis/io/wkt/wkt.hpp></span>
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<span class="keywordtype">int</span> main()
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{
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<span class="keywordflow">try</span>
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{
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<span class="comment">// establish database connection</span>
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soci::session sql(soci::postgresql, <span class="stringliteral">"dbname=ggl user=ggl password=ggl"</span>);
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<span class="comment">// construct schema of table for trees (point geometries)</span>
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sql << <span class="stringliteral">"DELETE FROM geometry_columns WHERE f_table_name = 'parcels'"</span>;
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sql << <span class="stringliteral">"DROP TABLE IF EXISTS parcels CASCADE"</span>;
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sql << <span class="stringliteral">"CREATE TABLE parcels (id INTEGER)"</span>;
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sql << <span class="stringliteral">"SELECT AddGeometryColumn('parcels', 'geom', -1, 'GEOMETRY', 2)"</span>;
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<span class="comment">// insert sample data using plain WKT input</span>
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sql << <span class="stringliteral">"INSERT INTO parcels VALUES(1, ST_GeomFromText('POLYGON ((10 10, 10 20, 20 20, 20 15, 10 10))', -1))"</span>;
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sql << <span class="stringliteral">"INSERT INTO parcels VALUES(2, ST_GeomFromText('POLYGON ((0 0, 4 0, 4 4, 0 4, 0 0))', -1))"</span>;
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sql << <span class="stringliteral">"INSERT INTO parcels VALUES(3, ST_GeomFromText('POLYGON((1 1,2 1,2 2,1 2,1 1))', -1))"</span>;
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<span class="comment">// query data in WKB form and read to geometry object</span>
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soci::rowset<std::string> rows = (sql.prepare << <span class="stringliteral">"SELECT encode(ST_AsBinary(geom), 'hex') AS wkb FROM parcels"</span>);
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<span class="comment">// calculate area of each parcel</span>
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<span class="keywordflow">for</span> (soci::rowset<std::string>::iterator it = rows.begin(); it != rows.end(); ++it)
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{
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<span class="comment">// parse WKB and construct geometry object</span>
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std::string <span class="keyword">const</span>& hex = *it;
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std::vector<unsigned char> wkb;
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<span class="keywordflow">if</span> (!boost::geometry::hex2wkb(*it, std::back_inserter(wkb)))
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<span class="keywordflow">throw</span> std::runtime_error(<span class="stringliteral">"hex2wkb translation failed"</span>);
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<a name="_a0"></a><a class="code" href="classboost_1_1geometry_1_1polygon.html" title="The polygon contains an outer ring and zero or more inner rings.">boost::geometry::polygon_2d</a> parcel;
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<span class="keywordflow">if</span> (!boost::geometry::read_wkb(wkb.begin(), wkb.end(), parcel))
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<span class="keywordflow">throw</span> std::runtime_error(<span class="stringliteral">"read_wkb failed"</span>);
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<span class="keywordtype">double</span> a = <a name="a1"></a><a class="code" href="group__area.html#gd0e9e99685a9d45895162bd1fd96a136" title="Calculate area of a geometry.">boost::geometry::area</a>(parcel);
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std::cout << <span class="stringliteral">"Parcel geometry: "</span> << boost::geometry::wkt(parcel) << std::endl
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<< <span class="stringliteral">"\thas area is "</span> << a << <span class="stringliteral">" in coordinate units"</span> << std::endl;
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}
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}
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<span class="keywordflow">catch</span> (std::exception <span class="keyword">const</span> &e)
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{
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std::cerr << <span class="stringliteral">"Error: "</span> << e.what() << <span class="charliteral">'\n'</span>;
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}
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<span class="keywordflow">return</span> 0;
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}
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</pre></div> </div>
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<td align="left"><small>
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<p>December 1, 2009</p>
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</small></td>
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<small>Copyright © 1995-2009 Barend Gehrels, Geodan, Amsterdam<br>
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Copyright © 2008-2009 Bruno Lalande, Paris<br>
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Copyright © 2009 Mateusz Loskot, Cadcorp, London<br>
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