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  26 <div class="titlepage"><div><div><h5 class="title">
  27 <a name="geometry.reference.algorithms.difference.difference_3"></a><a class="link" href="difference_3.html" title="difference">difference</a>
  28 </h5></div></div></div>
  29 <p>
  30             <a class="indexterm" name="idm46187003403424"></a>
  31           </p>
  32 <h6>
  33 <a name="geometry.reference.algorithms.difference.difference_3.h0"></a>
  34             <span class="phrase"><a name="geometry.reference.algorithms.difference.difference_3.description"></a></span><a class="link" href="difference_3.html#geometry.reference.algorithms.difference.difference_3.description">Description</a>
  35           </h6>
  36 <p>
  37             Calculate the difference of two geometries
  38           </p>
  39 <p>
  40             The free function difference calculates the spatial set theoretic difference
  41             of two geometries.
  42           </p>
  43 <h6>
  44 <a name="geometry.reference.algorithms.difference.difference_3.h1"></a>
  45             <span class="phrase"><a name="geometry.reference.algorithms.difference.difference_3.synopsis"></a></span><a class="link" href="difference_3.html#geometry.reference.algorithms.difference.difference_3.synopsis">Synopsis</a>
  46           </h6>
  47 <p>
  48 </p>
  49 <pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Geometry1</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Geometry2</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Collection</span><span class="special">&gt;</span>
  50 <span class="keyword">void</span> <span class="identifier">difference</span><span class="special">(</span><span class="identifier">Geometry1</span> <span class="keyword">const</span> <span class="special">&amp;</span> <span class="identifier">geometry1</span><span class="special">,</span> <span class="identifier">Geometry2</span> <span class="keyword">const</span> <span class="special">&amp;</span> <span class="identifier">geometry2</span><span class="special">,</span> <span class="identifier">Collection</span> <span class="special">&amp;</span> <span class="identifier">output_collection</span><span class="special">)</span></pre>
  51 <p>
  52           </p>
  53 <h6>
  54 <a name="geometry.reference.algorithms.difference.difference_3.h2"></a>
  55             <span class="phrase"><a name="geometry.reference.algorithms.difference.difference_3.parameters"></a></span><a class="link" href="difference_3.html#geometry.reference.algorithms.difference.difference_3.parameters">Parameters</a>
  56           </h6>
  57 <div class="informaltable"><table class="table">
  58 <colgroup>
  59 <col>
  60 <col>
  61 <col>
  62 <col>
  63 </colgroup>
  64 <thead><tr>
  65 <th>
  66                     <p>
  67                       Type
  68                     </p>
  69                   </th>
  70 <th>
  71                     <p>
  72                       Concept
  73                     </p>
  74                   </th>
  75 <th>
  76                     <p>
  77                       Name
  78                     </p>
  79                   </th>
  80 <th>
  81                     <p>
  82                       Description
  83                     </p>
  84                   </th>
  85 </tr></thead>
  86 <tbody>
  87 <tr>
  88 <td>
  89                     <p>
  90                       Geometry1 const &amp;
  91                     </p>
  92                   </td>
  93 <td>
  94                     <p>
  95                       Any type fulfilling a Geometry Concept
  96                     </p>
  97                   </td>
  98 <td>
  99                     <p>
 100                       geometry1
 101                     </p>
 102                   </td>
 103 <td>
 104                     <p>
 105                       A model of the specified concept
 106                     </p>
 107                   </td>
 108 </tr>
 109 <tr>
 110 <td>
 111                     <p>
 112                       Geometry2 const &amp;
 113                     </p>
 114                   </td>
 115 <td>
 116                     <p>
 117                       Any type fulfilling a Geometry Concept
 118                     </p>
 119                   </td>
 120 <td>
 121                     <p>
 122                       geometry2
 123                     </p>
 124                   </td>
 125 <td>
 126                     <p>
 127                       A model of the specified concept
 128                     </p>
 129                   </td>
 130 </tr>
 131 <tr>
 132 <td>
 133                     <p>
 134                       Collection &amp;
 135                     </p>
 136                   </td>
 137 <td>
 138                     <p>
 139                       output collection, either a multi-geometry, or a std::vector&lt;Geometry&gt;
 140                       / std::deque&lt;Geometry&gt; etc
 141                     </p>
 142                   </td>
 143 <td>
 144                     <p>
 145                       output_collection
 146                     </p>
 147                   </td>
 148 <td>
 149                     <p>
 150                       the output collection
 151                     </p>
 152                   </td>
 153 </tr>
 154 </tbody>
 155 </table></div>
 156 <h6>
 157 <a name="geometry.reference.algorithms.difference.difference_3.h3"></a>
 158             <span class="phrase"><a name="geometry.reference.algorithms.difference.difference_3.header"></a></span><a class="link" href="difference_3.html#geometry.reference.algorithms.difference.difference_3.header">Header</a>
 159           </h6>
 160 <p>
 161             Either
 162           </p>
 163 <p>
 164             <code class="computeroutput"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">geometry</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
 165           </p>
 166 <p>
 167             Or
 168           </p>
 169 <p>
 170             <code class="computeroutput"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">geometry</span><span class="special">/</span><span class="identifier">algorithms</span><span class="special">/</span><span class="identifier">difference</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
 171           </p>
 172 <h6>
 173 <a name="geometry.reference.algorithms.difference.difference_3.h4"></a>
 174             <span class="phrase"><a name="geometry.reference.algorithms.difference.difference_3.conformance"></a></span><a class="link" href="difference_3.html#geometry.reference.algorithms.difference.difference_3.conformance">Conformance</a>
 175           </h6>
 176 <p>
 177             The function difference implements function Difference from the <a href="http://www.opengeospatial.org/standards/sfa" target="_top">OGC Simple Feature
 178             Specification</a>.
 179           </p>
 180 <h6>
 181 <a name="geometry.reference.algorithms.difference.difference_3.h5"></a>
 182             <span class="phrase"><a name="geometry.reference.algorithms.difference.difference_3.behavior"></a></span><a class="link" href="difference_3.html#geometry.reference.algorithms.difference.difference_3.behavior">Behavior</a>
 183           </h6>
 184 <div class="informaltable"><table class="table">
 185 <colgroup>
 186 <col>
 187 <col>
 188 </colgroup>
 189 <thead><tr>
 190 <th>
 191                     <p>
 192                       Case
 193                     </p>
 194                   </th>
 195 <th>
 196                     <p>
 197                       Behavior
 198                     </p>
 199                   </th>
 200 </tr></thead>
 201 <tbody>
 202 <tr>
 203 <td>
 204                     <p>
 205                       areal (e.g. polygon)
 206                     </p>
 207                   </td>
 208 <td>
 209                     <p>
 210                       All combinations of: box, ring, polygon, multi_polygon
 211                     </p>
 212                   </td>
 213 </tr>
 214 <tr>
 215 <td>
 216                     <p>
 217                       linear (e.g. linestring) / areal (e.g. polygon)
 218                     </p>
 219                   </td>
 220 <td>
 221                     <p>
 222                       A combinations of a (multi) linestring with a (multi) polygon
 223                       results in a collection of linestrings
 224                     </p>
 225                   </td>
 226 </tr>
 227 <tr>
 228 <td>
 229                     <p>
 230                       linear (e.g. linestring)
 231                     </p>
 232                   </td>
 233 <td>
 234                     <p>
 235                       All combinations of: linestring, multi_linestring; results
 236                       in a collection of linestrings
 237                     </p>
 238                   </td>
 239 </tr>
 240 <tr>
 241 <td>
 242                     <p>
 243                       pointlike (e.g. point)
 244                     </p>
 245                   </td>
 246 <td>
 247                     <p>
 248                       All combinations of: point, multi_point; results in a collection
 249                       of points
 250                     </p>
 251                   </td>
 252 </tr>
 253 <tr>
 254 <td>
 255                     <p>
 256                       Other geometries
 257                     </p>
 258                   </td>
 259 <td>
 260                     <p>
 261                       Not yet supported in this version
 262                     </p>
 263                   </td>
 264 </tr>
 265 <tr>
 266 <td>
 267                     <p>
 268                       Spherical
 269                     </p>
 270                   </td>
 271 <td>
 272                     <p>
 273                       Not yet supported in this version
 274                     </p>
 275                   </td>
 276 </tr>
 277 <tr>
 278 <td>
 279                     <p>
 280                       Three dimensional
 281                     </p>
 282                   </td>
 283 <td>
 284                     <p>
 285                       Not yet supported in this version
 286                     </p>
 287                   </td>
 288 </tr>
 289 </tbody>
 290 </table></div>
 291 <div class="note"><table border="0" summary="Note">
 292 <tr>
 293 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../../../doc/src/images/note.png"></td>
 294 <th align="left">Note</th>
 295 </tr>
 296 <tr><td align="left" valign="top"><p>
 297               Check the <a class="link" href="../../concepts/concept_polygon.html" title="Polygon Concept">Polygon
 298               Concept</a> for the rules that polygon input for this algorithm
 299               should fulfill
 300             </p></td></tr>
 301 </table></div>
 302 <h6>
 303 <a name="geometry.reference.algorithms.difference.difference_3.h6"></a>
 304             <span class="phrase"><a name="geometry.reference.algorithms.difference.difference_3.example"></a></span><a class="link" href="difference_3.html#geometry.reference.algorithms.difference.difference_3.example">Example</a>
 305           </h6>
 306 <p>
 307             Shows how to subtract one polygon from another polygon
 308           </p>
 309 <p>
 310 </p>
 311 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
 312 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">list</span><span class="special">&gt;</span>
 313
 314 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">geometry</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 315 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">geometry</span><span class="special">/</span><span class="identifier">geometries</span><span class="special">/</span><span class="identifier">point_xy</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 316 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">geometry</span><span class="special">/</span><span class="identifier">geometries</span><span class="special">/</span><span class="identifier">polygon</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 317
 318 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">foreach</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 319
 320
 321 <span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
 322 <span class="special">{</span>
 323     <span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">model</span><span class="special">::</span><span class="identifier">polygon</span><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">model</span><span class="special">::</span><span class="identifier">d2</span><span class="special">::</span><span class="identifier">point_xy</span><span class="special">&lt;</span><span class="keyword">double</span><span class="special">&gt;</span> <span class="special">&gt;</span> <span class="identifier">polygon</span><span class="special">;</span>
 324
 325     <span class="identifier">polygon</span> <span class="identifier">green</span><span class="special">,</span> <span class="identifier">blue</span><span class="special">;</span>
 326
 327     <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">read_wkt</span><span class="special">(</span>
 328         <span class="string">"POLYGON((2 1.3,2.4 1.7,2.8 1.8,3.4 1.2,3.7 1.6,3.4 2,4.1 3,5.3 2.6,5.4 1.2,4.9 0.8,2.9 0.7,2 1.3)"</span>
 329             <span class="string">"(4.0 2.0, 4.2 1.4, 4.8 1.9, 4.4 2.2, 4.0 2.0))"</span><span class="special">,</span> <span class="identifier">green</span><span class="special">);</span>
 330
 331     <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">read_wkt</span><span class="special">(</span>
 332         <span class="string">"POLYGON((4.0 -0.5 , 3.5 1.0 , 2.0 1.5 , 3.5 2.0 , 4.0 3.5 , 4.5 2.0 , 6.0 1.5 , 4.5 1.0 , 4.0 -0.5))"</span><span class="special">,</span> <span class="identifier">blue</span><span class="special">);</span>
 333
 334     <span class="identifier">std</span><span class="special">::</span><span class="identifier">list</span><span class="special">&lt;</span><span class="identifier">polygon</span><span class="special">&gt;</span> <span class="identifier">output</span><span class="special">;</span>
 335     <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">difference</span><span class="special">(</span><span class="identifier">green</span><span class="special">,</span> <span class="identifier">blue</span><span class="special">,</span> <span class="identifier">output</span><span class="special">);</span>
 336
 337     <span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
 338     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"green - blue:"</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 339     <span class="identifier">BOOST_FOREACH</span><span class="special">(</span><span class="identifier">polygon</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">p</span><span class="special">,</span> <span class="identifier">output</span><span class="special">)</span>
 340     <span class="special">{</span>
 341         <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">i</span><span class="special">++</span> <span class="special">&lt;&lt;</span> <span class="string">": "</span> <span class="special">&lt;&lt;</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">area</span><span class="special">(</span><span class="identifier">p</span><span class="special">)</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 342     <span class="special">}</span>
 343
 344
 345     <span class="identifier">output</span><span class="special">.</span><span class="identifier">clear</span><span class="special">();</span>
 346     <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">difference</span><span class="special">(</span><span class="identifier">blue</span><span class="special">,</span> <span class="identifier">green</span><span class="special">,</span> <span class="identifier">output</span><span class="special">);</span>
 347
 348     <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
 349     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"blue - green:"</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 350     <span class="identifier">BOOST_FOREACH</span><span class="special">(</span><span class="identifier">polygon</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">p</span><span class="special">,</span> <span class="identifier">output</span><span class="special">)</span>
 351     <span class="special">{</span>
 352         <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">i</span><span class="special">++</span> <span class="special">&lt;&lt;</span> <span class="string">": "</span> <span class="special">&lt;&lt;</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">area</span><span class="special">(</span><span class="identifier">p</span><span class="special">)</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 353     <span class="special">}</span>
 354
 355
 356     <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
 357 <span class="special">}</span>
 358 </pre>
 359 <p>
 360           </p>
 361 <p>
 362             Output:
 363           </p>
 364 <pre class="programlisting">green - blue:
 365 0: 0.02375
 366 1: 0.542951
 367 2: 0.0149697
 368 3: 0.226855
 369 4: 0.839424
 370
 371 <img src="../../../../img/algorithms/difference_a.png" alt="difference_a">
 372
 373 blue - green:
 374 0: 0.525154
 375 1: 0.015
 376 2: 0.181136
 377 3: 0.128798
 378 4: 0.340083
 379 5: 0.307778
 380
 381 <img src="../../../../img/algorithms/difference_b.png" alt="difference_b">
 382 </pre>
 383 <h6>
 384 <a name="geometry.reference.algorithms.difference.difference_3.h7"></a>
 385             <span class="phrase"><a name="geometry.reference.algorithms.difference.difference_3.see_also"></a></span><a class="link" href="difference_3.html#geometry.reference.algorithms.difference.difference_3.see_also">See
 386             also</a>
 387           </h6>
 388 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 389 <li class="listitem">
 390                 <a class="link" href="../sym_difference.html" title="sym_difference">sym_difference
 391                 (symmetric difference)</a>
 392               </li>
 393 <li class="listitem">
 394                 <a class="link" href="../intersection.html" title="intersection">intersection</a>
 395               </li>
 396 <li class="listitem">
 397                 <a class="link" href="../union_.html" title="union_">union</a>
 398               </li>
 399 </ul></div>
 400 </div>
 401 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 402 <td align="left"></td>
 403 <td align="right"><div class="copyright-footer">Copyright &#169; 2009-2019 Barend Gehrels, Bruno Lalande, Mateusz Loskot, Adam
 404       Wulkiewicz, Oracle and/or its affiliates<p>
 405         Distributed under the Boost Software License, Version 1.0. (See accompanying
 406         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
 407       </p>
 408 </div></td>
 409 </tr></table>
 410 <hr>
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