libs/geometry/doc/html/geometry/reference/algorithms/centroid/centroid_2.html

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  25 <div class="section">
  26 <div class="titlepage"><div><div><h5 class="title">
  27 <a name="geometry.reference.algorithms.centroid.centroid_2"></a><a class="link" href="centroid_2.html" title="centroid">centroid</a>
  28 </h5></div></div></div>
  29 <p>
  30             <a class="indexterm" name="idm46187007398912"></a>
  31 Calculates the centroid of a geometry.
  32           </p>
  33 <h6>
  34 <a name="geometry.reference.algorithms.centroid.centroid_2.h0"></a>
  35             <span class="phrase"><a name="geometry.reference.algorithms.centroid.centroid_2.description"></a></span><a class="link" href="centroid_2.html#geometry.reference.algorithms.centroid.centroid_2.description">Description</a>
  36           </h6>
  37 <p>
  38             The free function centroid calculates the geometric center (or: center
  39             of mass) of a geometry. It uses the default strategy, based on the coordinate
  40             system of the geometry.
  41           </p>
  42 <h6>
  43 <a name="geometry.reference.algorithms.centroid.centroid_2.h1"></a>
  44             <span class="phrase"><a name="geometry.reference.algorithms.centroid.centroid_2.synopsis"></a></span><a class="link" href="centroid_2.html#geometry.reference.algorithms.centroid.centroid_2.synopsis">Synopsis</a>
  45           </h6>
  46 <p>
  47 </p>
  48 <pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Geometry</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Point</span><span class="special">&gt;</span>
  49 <span class="keyword">void</span> <span class="identifier">centroid</span><span class="special">(</span><span class="identifier">Geometry</span> <span class="keyword">const</span> <span class="special">&amp;</span> <span class="identifier">geometry</span><span class="special">,</span> <span class="identifier">Point</span> <span class="special">&amp;</span> <span class="identifier">c</span><span class="special">)</span></pre>
  50 <p>
  51           </p>
  52 <h6>
  53 <a name="geometry.reference.algorithms.centroid.centroid_2.h2"></a>
  54             <span class="phrase"><a name="geometry.reference.algorithms.centroid.centroid_2.parameters"></a></span><a class="link" href="centroid_2.html#geometry.reference.algorithms.centroid.centroid_2.parameters">Parameters</a>
  55           </h6>
  56 <div class="informaltable"><table class="table">
  57 <colgroup>
  58 <col>
  59 <col>
  60 <col>
  61 <col>
  62 </colgroup>
  63 <thead><tr>
  64 <th>
  65                     <p>
  66                       Type
  67                     </p>
  68                   </th>
  69 <th>
  70                     <p>
  71                       Concept
  72                     </p>
  73                   </th>
  74 <th>
  75                     <p>
  76                       Name
  77                     </p>
  78                   </th>
  79 <th>
  80                     <p>
  81                       Description
  82                     </p>
  83                   </th>
  84 </tr></thead>
  85 <tbody>
  86 <tr>
  87 <td>
  88                     <p>
  89                       Geometry const &amp;
  90                     </p>
  91                   </td>
  92 <td>
  93                     <p>
  94                       Any type fulfilling a Geometry Concept
  95                     </p>
  96                   </td>
  97 <td>
  98                     <p>
  99                       geometry
 100                     </p>
 101                   </td>
 102 <td>
 103                     <p>
 104                       A model of the specified concept
 105                     </p>
 106                   </td>
 107 </tr>
 108 <tr>
 109 <td>
 110                     <p>
 111                       Point &amp;
 112                     </p>
 113                   </td>
 114 <td>
 115                     <p>
 116                       Any type fulfilling a Point Concept
 117                     </p>
 118                   </td>
 119 <td>
 120                     <p>
 121                       c
 122                     </p>
 123                   </td>
 124 <td>
 125                     <p>
 126                       The calculated centroid will be assigned to this point reference
 127                     </p>
 128                   </td>
 129 </tr>
 130 </tbody>
 131 </table></div>
 132 <h6>
 133 <a name="geometry.reference.algorithms.centroid.centroid_2.h3"></a>
 134             <span class="phrase"><a name="geometry.reference.algorithms.centroid.centroid_2.header"></a></span><a class="link" href="centroid_2.html#geometry.reference.algorithms.centroid.centroid_2.header">Header</a>
 135           </h6>
 136 <p>
 137             Either
 138           </p>
 139 <p>
 140             <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>
 141           </p>
 142 <p>
 143             Or
 144           </p>
 145 <p>
 146             <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">centroid</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
 147           </p>
 148 <h6>
 149 <a name="geometry.reference.algorithms.centroid.centroid_2.h4"></a>
 150             <span class="phrase"><a name="geometry.reference.algorithms.centroid.centroid_2.conformance"></a></span><a class="link" href="centroid_2.html#geometry.reference.algorithms.centroid.centroid_2.conformance">Conformance</a>
 151           </h6>
 152 <p>
 153             The function centroid implements function Centroid from the <a href="http://www.opengeospatial.org/standards/sfa" target="_top">OGC
 154             Simple Feature Specification</a>.
 155           </p>
 156 <h6>
 157 <a name="geometry.reference.algorithms.centroid.centroid_2.h5"></a>
 158             <span class="phrase"><a name="geometry.reference.algorithms.centroid.centroid_2.behavior"></a></span><a class="link" href="centroid_2.html#geometry.reference.algorithms.centroid.centroid_2.behavior">Behavior</a>
 159           </h6>
 160 <div class="informaltable"><table class="table">
 161 <colgroup>
 162 <col>
 163 <col>
 164 </colgroup>
 165 <thead><tr>
 166 <th>
 167                     <p>
 168                       Case
 169                     </p>
 170                   </th>
 171 <th>
 172                     <p>
 173                       Behavior
 174                     </p>
 175                   </th>
 176 </tr></thead>
 177 <tbody>
 178 <tr>
 179 <td>
 180                     <p>
 181                       Point
 182                     </p>
 183                   </td>
 184 <td>
 185                     <p>
 186                       Returns the point itself as the centroid
 187                     </p>
 188                   </td>
 189 </tr>
 190 <tr>
 191 <td>
 192                     <p>
 193                       Multi Point
 194                     </p>
 195                   </td>
 196 <td>
 197                     <p>
 198                       Calculates centroid (based on average)
 199                     </p>
 200                   </td>
 201 </tr>
 202 <tr>
 203 <td>
 204                     <p>
 205                       linear (e.g. linestring)
 206                     </p>
 207                   </td>
 208 <td>
 209                     <p>
 210                       Calculates centroid (based on weighted length)
 211                     </p>
 212                   </td>
 213 </tr>
 214 <tr>
 215 <td>
 216                     <p>
 217                       areal (e.g. polygon)
 218                     </p>
 219                   </td>
 220 <td>
 221                     <p>
 222                       Calculates centroid
 223                     </p>
 224                   </td>
 225 </tr>
 226 <tr>
 227 <td>
 228                     <p>
 229                       Empty (e.g. polygon without points)
 230                     </p>
 231                   </td>
 232 <td>
 233                     <p>
 234                       Throws a <a class="link" href="../../exceptions/centroid_exception.html" title="centroid_exception">centroid_exception</a>
 235                     </p>
 236                   </td>
 237 </tr>
 238 <tr>
 239 <td>
 240                     <p>
 241                       Cartesian
 242                     </p>
 243                   </td>
 244 <td>
 245                     <p>
 246                       Implemented
 247                     </p>
 248                   </td>
 249 </tr>
 250 <tr>
 251 <td>
 252                     <p>
 253                       Spherical
 254                     </p>
 255                   </td>
 256 <td>
 257                     <p>
 258                       Calculates the centroid as if based on Cartesian coordinates
 259                     </p>
 260                   </td>
 261 </tr>
 262 </tbody>
 263 </table></div>
 264 <h6>
 265 <a name="geometry.reference.algorithms.centroid.centroid_2.h6"></a>
 266             <span class="phrase"><a name="geometry.reference.algorithms.centroid.centroid_2.supported_geometries"></a></span><a class="link" href="centroid_2.html#geometry.reference.algorithms.centroid.centroid_2.supported_geometries">Supported
 267             geometries</a>
 268           </h6>
 269 <div class="informaltable"><table class="table">
 270 <colgroup>
 271 <col>
 272 <col>
 273 <col>
 274 </colgroup>
 275 <thead><tr>
 276 <th>
 277                   </th>
 278 <th>
 279                     <p>
 280                       2D
 281                     </p>
 282                   </th>
 283 <th>
 284                     <p>
 285                       3D
 286                     </p>
 287                   </th>
 288 </tr></thead>
 289 <tbody>
 290 <tr>
 291 <td>
 292                     <p>
 293                       Point
 294                     </p>
 295                   </td>
 296 <td>
 297                     <p>
 298                       <span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
 299                     </p>
 300                   </td>
 301 <td>
 302                     <p>
 303                       <span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
 304                     </p>
 305                   </td>
 306 </tr>
 307 <tr>
 308 <td>
 309                     <p>
 310                       Segment
 311                     </p>
 312                   </td>
 313 <td>
 314                     <p>
 315                       <span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
 316                     </p>
 317                   </td>
 318 <td>
 319                     <p>
 320                       <span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
 321                     </p>
 322                   </td>
 323 </tr>
 324 <tr>
 325 <td>
 326                     <p>
 327                       Box
 328                     </p>
 329                   </td>
 330 <td>
 331                     <p>
 332                       <span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
 333                     </p>
 334                   </td>
 335 <td>
 336                     <p>
 337                       <span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
 338                     </p>
 339                   </td>
 340 </tr>
 341 <tr>
 342 <td>
 343                     <p>
 344                       Linestring
 345                     </p>
 346                   </td>
 347 <td>
 348                     <p>
 349                       <span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
 350                     </p>
 351                   </td>
 352 <td>
 353                     <p>
 354                       <span class="inlinemediaobject"><img src="../../../../img/nyi.png" alt="nyi"></span>
 355                     </p>
 356                   </td>
 357 </tr>
 358 <tr>
 359 <td>
 360                     <p>
 361                       Ring
 362                     </p>
 363                   </td>
 364 <td>
 365                     <p>
 366                       <span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
 367                     </p>
 368                   </td>
 369 <td>
 370                     <p>
 371                       <span class="inlinemediaobject"><img src="../../../../img/nyi.png" alt="nyi"></span>
 372                     </p>
 373                   </td>
 374 </tr>
 375 <tr>
 376 <td>
 377                     <p>
 378                       Polygon
 379                     </p>
 380                   </td>
 381 <td>
 382                     <p>
 383                       <span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
 384                     </p>
 385                   </td>
 386 <td>
 387                     <p>
 388                       <span class="inlinemediaobject"><img src="../../../../img/nyi.png" alt="nyi"></span>
 389                     </p>
 390                   </td>
 391 </tr>
 392 <tr>
 393 <td>
 394                     <p>
 395                       MultiPoint
 396                     </p>
 397                   </td>
 398 <td>
 399                     <p>
 400                       <span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
 401                     </p>
 402                   </td>
 403 <td>
 404                     <p>
 405                       <span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
 406                     </p>
 407                   </td>
 408 </tr>
 409 <tr>
 410 <td>
 411                     <p>
 412                       MultiLinestring
 413                     </p>
 414                   </td>
 415 <td>
 416                     <p>
 417                       <span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
 418                     </p>
 419                   </td>
 420 <td>
 421                     <p>
 422                       <span class="inlinemediaobject"><img src="../../../../img/nyi.png" alt="nyi"></span>
 423                     </p>
 424                   </td>
 425 </tr>
 426 <tr>
 427 <td>
 428                     <p>
 429                       MultiPolygon
 430                     </p>
 431                   </td>
 432 <td>
 433                     <p>
 434                       <span class="inlinemediaobject"><img src="../../../../img/ok.png" alt="ok"></span>
 435                     </p>
 436                   </td>
 437 <td>
 438                     <p>
 439                       <span class="inlinemediaobject"><img src="../../../../img/nyi.png" alt="nyi"></span>
 440                     </p>
 441                   </td>
 442 </tr>
 443 </tbody>
 444 </table></div>
 445 <h6>
 446 <a name="geometry.reference.algorithms.centroid.centroid_2.h7"></a>
 447             <span class="phrase"><a name="geometry.reference.algorithms.centroid.centroid_2.complexity"></a></span><a class="link" href="centroid_2.html#geometry.reference.algorithms.centroid.centroid_2.complexity">Complexity</a>
 448           </h6>
 449 <p>
 450             Linear
 451           </p>
 452 <h6>
 453 <a name="geometry.reference.algorithms.centroid.centroid_2.h8"></a>
 454             <span class="phrase"><a name="geometry.reference.algorithms.centroid.centroid_2.example"></a></span><a class="link" href="centroid_2.html#geometry.reference.algorithms.centroid.centroid_2.example">Example</a>
 455           </h6>
 456 <p>
 457             Shows calculation of a centroid of a polygon
 458           </p>
 459 <p>
 460 </p>
 461 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
 462 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">list</span><span class="special">&gt;</span>
 463
 464 <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>
 465 <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>
 466 <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>
 467
 468
 469 <span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
 470 <span class="special">{</span>
 471     <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">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="identifier">point_type</span><span class="special">;</span>
 472     <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">point_type</span><span class="special">&gt;</span> <span class="identifier">polygon_type</span><span class="special">;</span>
 473
 474     <span class="identifier">polygon_type</span> <span class="identifier">poly</span><span class="special">;</span>
 475     <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>
 476         <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>
 477             <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">poly</span><span class="special">);</span>
 478
 479     <span class="identifier">point_type</span> <span class="identifier">p</span><span class="special">;</span>
 480     <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">centroid</span><span class="special">(</span><span class="identifier">poly</span><span class="special">,</span> <span class="identifier">p</span><span class="special">);</span>
 481
 482     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"centroid: "</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">dsv</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>
 483
 484     <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
 485 <span class="special">}</span>
 486 </pre>
 487 <p>
 488           </p>
 489 <p>
 490             Output:
 491           </p>
 492 <pre class="programlisting">centroid: (4.04663, 1.6349)
 493 <img src="../../../../img/algorithms/centroid.png" alt="centroid">
 494 </pre>
 495 <p>
 496             Note that the centroid might be located in a hole or outside a polygon,
 497             easily.
 498           </p>
 499 </div>
 500 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 501 <td align="left"></td>
 502 <td align="right"><div class="copyright-footer">Copyright &#169; 2009-2019 Barend Gehrels, Bruno Lalande, Mateusz Loskot, Adam
 503       Wulkiewicz, Oracle and/or its affiliates<p>
 504         Distributed under the Boost Software License, Version 1.0. (See accompanying
 505         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>)
 506       </p>
 507 </div></td>
 508 </tr></table>
 509 <hr>
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