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      <a name="opengis-geometry-model">
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      13.4.2 The OpenGIS Geometry Model
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     <span class="section">
      <a href="gis-geometry-class-hierarchy.html">
       13.4.2.1 The Geometry Class Hierarchy
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      <a href="gis-class-geometry.html">
       13.4.2.2 Geometry Class
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      <a href="gis-class-point.html">
       13.4.2.3 Point Class
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      <a href="gis-class-curve.html">
       13.4.2.4 Curve Class
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      <a href="gis-class-linestring.html">
       13.4.2.5 LineString Class
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      <a href="gis-class-surface.html">
       13.4.2.6 Surface Class
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      <a href="gis-class-polygon.html">
       13.4.2.7 Polygon Class
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      <a href="gis-class-geometrycollection.html">
       13.4.2.8 GeometryCollection Class
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      <a href="gis-class-multipoint.html">
       13.4.2.9 MultiPoint Class
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      <a href="gis-class-multicurve.html">
       13.4.2.10 MultiCurve Class
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      <a href="gis-class-multilinestring.html">
       13.4.2.11 MultiLineString Class
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      <a href="gis-class-multisurface.html">
       13.4.2.12 MultiSurface Class
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      <a href="gis-class-multipolygon.html">
       13.4.2.13 MultiPolygon Class
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  <p>
   The set of geometry types proposed by OGC's
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    <strong>
     SQL with Geometry Types
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   environment is based on the
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    <strong>
     OpenGIS
        Geometry Model
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   . In this model, each geometric object
        has the following general properties:
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      It is associated with a spatial reference system, which
            describes the coordinate space in which the object is
            defined.
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      It belongs to some geometry class.
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