Expose GEOS clip by rect algorithm via QgsGeometry API

Performs a fast, non-robust intersection between the geometry and
a rectangle. The returned geometry may be invalid.

Author: nyalldawson

python/core/geometry/qgsgeometry.sip

@@ -828,6 +828,16 @@ Returns a geometry representing the points shared by this geometry and other.
  :rtype: QgsGeometry
 %End
 
+    QgsGeometry clipped( const QgsRectangle &rectangle );
+%Docstring
+ Clips the geometry using the specified ``rectangle``.
+
+ Performs a fast, non-robust intersection between the geometry and
+ a ``rectangle``. The returned geometry may be invalid.
+.. versionadded:: 3.0
+ :rtype: QgsGeometry
+%End
+
     QgsGeometry combine( const QgsGeometry &geometry ) const;
 %Docstring
  Returns a geometry representing all the points in this geometry and other (a
@@ -1129,7 +1139,6 @@ Ring 0 is outer ring and can't be deleted.
 .. versionadded:: 2.10
 %End
 
-
     void draw( QPainter &p ) const;
 %Docstring
  Draws the geometry onto a QPainter

src/core/geometry/qgsgeometry.cpp

@@ -2089,17 +2089,17 @@ void QgsGeometry::mapToPixel( const QgsMapToPixel &mtp )
   }
 }
 
-#if 0
-void QgsGeometry::clip( const QgsRectangle &rect )
+QgsGeometry QgsGeometry::clipped( const QgsRectangle &rectangle )
 {
-  if ( d->geometry )
+  if ( !d->geometry || rectangle.isNull() || rectangle.isEmpty() )
   {
-    detach();
-    d->geometry->clip( rect );
-    removeWkbGeos();
+    return QgsGeometry();
   }
+
+  QgsGeos geos( d->geometry );
+  QgsAbstractGeometry *resultGeom = geos.clip( rectangle );
+  return QgsGeometry( resultGeom );
 }
-#endif
 
 void QgsGeometry::draw( QPainter &p ) const
 {

src/core/geometry/qgsgeometry.h

@@ -765,6 +765,15 @@ class CORE_EXPORT QgsGeometry
     //! Returns a geometry representing the points shared by this geometry and other.
     QgsGeometry intersection( const QgsGeometry &geometry ) const;
 
+    /**
+     * Clips the geometry using the specified \a rectangle.
+     *
+     * Performs a fast, non-robust intersection between the geometry and
+     * a \a rectangle. The returned geometry may be invalid.
+     * \since QGIS 3.0
+     */
+    QgsGeometry clipped( const QgsRectangle &rectangle );
+
     /** Returns a geometry representing all the points in this geometry and other (a
      * union geometry operation).
      * \note this operation is not called union since its a reserved word in C++.
@@ -999,13 +1008,6 @@ class CORE_EXPORT QgsGeometry
      */
     void mapToPixel( const QgsMapToPixel &mtp );
 
-    // not implemented for 2.10
-    /* Clips the geometry using the specified rectangle
-     * \param rect clip rectangle
-     * \since QGIS 2.10
-     */
-    // void clip( const QgsRectangle& rect );
-
     /** Draws the geometry onto a QPainter
      * \param p destination QPainter
      * \since QGIS 2.10

src/core/geometry/qgsgeos.cpp

@@ -189,6 +189,30 @@ QgsAbstractGeometry *QgsGeos::difference( const QgsAbstractGeometry &geom, QStri
   return overlay( geom, DIFFERENCE, errorMsg );
 }
 
+QgsAbstractGeometry *QgsGeos::clip( const QgsRectangle &rect, QString *errorMsg ) const
+{
+  if ( !mGeos || rect.isNull() || rect.isEmpty() )
+  {
+    return nullptr;
+  }
+
+  try
+  {
+    GEOSGeomScopedPtr opGeom;
+    opGeom.reset( GEOSClipByRect_r( geosinit.ctxt, mGeos, rect.xMinimum(), rect.yMinimum(), rect.xMaximum(), rect.yMaximum() ) );
+    QgsAbstractGeometry *opResult = fromGeos( opGeom.get() );
+    return opResult;
+  }
+  catch ( GEOSException &e )
+  {
+    if ( errorMsg )
+    {
+      *errorMsg = e.what();
+    }
+    return nullptr;
+  }
+}
+
 QgsAbstractGeometry *QgsGeos::combine( const QgsAbstractGeometry &geom, QString *errorMsg ) const
 {
   return overlay( geom, UNION, errorMsg );

src/core/geometry/qgsgeos.h

@@ -45,6 +45,13 @@ class CORE_EXPORT QgsGeos: public QgsGeometryEngine
 
     QgsAbstractGeometry *intersection( const QgsAbstractGeometry &geom, QString *errorMsg = nullptr ) const override;
     QgsAbstractGeometry *difference( const QgsAbstractGeometry &geom, QString *errorMsg = nullptr ) const override;
+
+    /**
+     * Performs a fast, non-robust intersection between the geometry and
+     * a \a rectangle. The returned geometry may be invalid.
+     */
+    QgsAbstractGeometry *clip( const QgsRectangle &rectangle, QString *errorMsg = nullptr ) const;
+
     QgsAbstractGeometry *combine( const QgsAbstractGeometry &geom, QString *errorMsg = nullptr ) const override;
     QgsAbstractGeometry *combine( const QList< QgsAbstractGeometry *> &, QString *errorMsg = nullptr ) const override;
     QgsAbstractGeometry *symDifference( const QgsAbstractGeometry &geom, QString *errorMsg = nullptr ) const override;

tests/src/python/test_qgsgeometry.py

@@ -4165,6 +4165,33 @@ def testPoint(self):
         self.assertEqual(point_zm.z(), 3)
         self.assertEqual(point_zm.m(), 4)
 
+    def testClipped(self):
+        tests = [["LINESTRING (1 1,1 9,9 9,9 1)", QgsRectangle(0, 0, 10, 10), "LINESTRING (1 1,1 9,9 9,9 1)"],
+                 ["LINESTRING (-1 -9,-1 11,9 11)", QgsRectangle(0, 0, 10, 10), "GEOMETRYCOLLECTION ()"],
+                 ["LINESTRING (-1 5,5 5,9 9)", QgsRectangle(0, 0, 10, 10), "LINESTRING (0 5,5 5,9 9)"],
+                 ["LINESTRING (5 5,8 5,12 5)", QgsRectangle(0, 0, 10, 10), "LINESTRING (5 5,8 5,10 5)"],
+                 ["LINESTRING (5 -1,5 5,1 2,-3 2,1 6)", QgsRectangle(0, 0, 10, 10), "MULTILINESTRING ((5 0,5 5,1 2,0 2),(0 5,1 6))"],
+                 ["LINESTRING (0 3,0 5,0 7)", QgsRectangle(0, 0, 10, 10), "GEOMETRYCOLLECTION ()"],
+                 ["LINESTRING (0 3,0 5,-1 7)", QgsRectangle(0, 0, 10, 10), "GEOMETRYCOLLECTION ()"],
+                 ["LINESTRING (0 3,0 5,2 7)", QgsRectangle(0, 0, 10, 10), "LINESTRING (0 5,2 7)"],
+                 ["LINESTRING (2 1,0 0,1 2)", QgsRectangle(0, 0, 10, 10), "LINESTRING (2 1,0 0,1 2)"],
+                 ["LINESTRING (3 3,0 3,0 5,2 7)", QgsRectangle(0, 0, 10, 10), "MULTILINESTRING ((3 3,0 3),(0 5,2 7))"],
+                 ["LINESTRING (5 5,10 5,20 5)", QgsRectangle(0, 0, 10, 10), "LINESTRING (5 5,10 5)"],
+                 ["LINESTRING (3 3,0 6,3 9)", QgsRectangle(0, 0, 10, 10), "LINESTRING (3 3,0 6,3 9)"],
+                 ["POLYGON ((5 5,5 6,6 6,6 5,5 5))", QgsRectangle(0, 0, 10, 10), "POLYGON ((5 5,5 6,6 6,6 5,5 5))"],
+                 ["POLYGON ((15 15,15 16,16 16,16 15,15 15))", QgsRectangle(0, 0, 10, 10), "GEOMETRYCOLLECTION ()"],
+                 ["POLYGON ((-1 -1,-1 11,11 11,11 -1,-1 -1))", QgsRectangle(0, 0, 10, 10), "Polygon ((0 0, 0 10, 10 10, 10 0, 0 0))"],
+                 ["POLYGON ((-1 -1,-1 5,5 5,5 -1,-1 -1))", QgsRectangle(0, 0, 10, 10), "Polygon ((0 0, 0 5, 5 5, 5 0, 0 0))"],
+                 ["POLYGON ((-2 -2,-2 5,5 5,5 -2,-2 -2), (3 3,4 4,4 2,3 3))", QgsRectangle(0, 0, 10, 10), "Polygon ((0 0, 0 5, 5 5, 5 0, 0 0),(3 3, 4 4, 4 2, 3 3))"]
+                 ]
+        for t in tests:
+            input = QgsGeometry.fromWkt(t[0])
+            o = input.clipped(t[1])
+            exp = t[2]
+            result = o.exportToWkt()
+            self.assertTrue(compareWkt(result, exp, 0.00001),
+                            "clipped: mismatch Expected:\n{}\nGot:\n{}\n".format(exp, result))
+
 
 if __name__ == '__main__':
     unittest.main()