Add QgsGeometry::isSimple() - useful for self-intersection checks

python/core/geometry/qgsgeometry.sip

@@ -188,6 +188,19 @@ Returns true if WKB of the geometry is of WKBMulti* type
  :rtype: bool
 %End
 
+    bool isSimple() const;
+%Docstring
+ Determines whether the geometry is simple (according to OGC definition),
+ i.e. it has no anomalous geometric points, such as self-intersection or self-tangency.
+ Uses GEOS library for the test.
+.. note::
+
+   This is useful mainly for linestrings and linear rings. Polygons are simple by definition,
+ for checking anomalies in polygon geometries one can use isGeosValid().
+.. versionadded:: 3.0
+ :rtype: bool
+%End
+
     double area() const;
 %Docstring
  Returns the area of the geometry using GEOS

python/core/geometry/qgsgeometryengine.sip

@@ -155,6 +155,13 @@ class QgsGeometryEngine
  :rtype: bool
 %End
 
+    virtual bool isSimple( QString *errorMsg = 0 ) const = 0;
+%Docstring
+ Determines whether the geometry is simple (according to OGC definition).
+.. versionadded:: 3.0
+ :rtype: bool
+%End
+
     virtual int splitGeometry( const QgsLineString &splitLine,
                                QList<QgsAbstractGeometry *> &newGeometries,
                                bool topological,

src/core/geometry/qgsgeometry.cpp

@@ -1980,6 +1980,15 @@ bool QgsGeometry::isGeosValid() const
   return geos.isValid();
 }
 
+bool QgsGeometry::isSimple() const
+{
+  if ( !d->geometry )
+    return false;
+
+  QgsGeos geos( d->geometry );
+  return geos.isSimple();
+}
+
 bool QgsGeometry::isGeosEqual( const QgsGeometry &g ) const
 {
   if ( !d->geometry || !g.d->geometry )

src/core/geometry/qgsgeometry.h

@@ -213,6 +213,15 @@ class CORE_EXPORT QgsGeometry
      */
     bool isGeosValid() const;
 
+    /** Determines whether the geometry is simple (according to OGC definition),
+     * i.e. it has no anomalous geometric points, such as self-intersection or self-tangency.
+     * Uses GEOS library for the test.
+     * \note This is useful mainly for linestrings and linear rings. Polygons are simple by definition,
+     * for checking anomalies in polygon geometries one can use isGeosValid().
+     * \since QGIS 3.0
+     */
+    bool isSimple() const;
+
     /** Returns the area of the geometry using GEOS
       \since QGIS 1.5
      */

src/core/geometry/qgsgeometryengine.h

@@ -83,6 +83,11 @@ class CORE_EXPORT QgsGeometryEngine
     virtual bool isEqual( const QgsAbstractGeometry &geom, QString *errorMsg = nullptr ) const = 0;
     virtual bool isEmpty( QString *errorMsg ) const = 0;
 
+    /** Determines whether the geometry is simple (according to OGC definition).
+     * \since QGIS 3.0
+     */
+    virtual bool isSimple( QString *errorMsg = nullptr ) const = 0;
+
     virtual int splitGeometry( const QgsLineString &splitLine,
                                QList<QgsAbstractGeometry *> &newGeometries,
                                bool topological,

src/core/geometry/qgsgeos.cpp

@@ -1494,6 +1494,20 @@ bool QgsGeos::isEmpty( QString *errorMsg ) const
   CATCH_GEOS_WITH_ERRMSG( false );
 }
 
+bool QgsGeos::isSimple( QString *errorMsg ) const
+{
+  if ( !mGeos )
+  {
+    return false;
+  }
+
+  try
+  {
+    return GEOSisSimple_r( geosinit.ctxt, mGeos );
+  }
+  CATCH_GEOS_WITH_ERRMSG( false );
+}
+
 GEOSCoordSequence *QgsGeos::createCoordinateSequence( const QgsCurve *curve, double precision, bool forceClose )
 {
   bool segmentize = false;

src/core/geometry/qgsgeos.h

@@ -71,6 +71,7 @@ class CORE_EXPORT QgsGeos: public QgsGeometryEngine
     bool isValid( QString *errorMsg = nullptr ) const override;
     bool isEqual( const QgsAbstractGeometry &geom, QString *errorMsg = nullptr ) const override;
     bool isEmpty( QString *errorMsg = nullptr ) const override;
+    bool isSimple( QString *errorMsg = nullptr ) const override;
 
     /** Splits this geometry according to a given line.
     \param splitLine the line that splits the geometry

tests/src/core/testqgsgeometry.cpp

@@ -124,6 +124,8 @@ class TestQgsGeometry : public QObject
 
     void makeValid();
 
+    void isSimple();
+
   private:
     //! A helper method to do a render check to see if the geometry op is as expected
     bool renderCheck( const QString &testName, const QString &comment = QLatin1String( QLatin1String( "" ) ), int mismatchCount = 0 );
@@ -5423,5 +5425,32 @@ void TestQgsGeometry::makeValid()
   }
 }
 
+void TestQgsGeometry::isSimple()
+{
+  typedef QPair<QString, bool> InputWktAndExpectedResult;
+  QList<InputWktAndExpectedResult> geoms;
+  geoms << qMakePair( QString( "LINESTRING(0 0, 1 0, 1 1)" ), true );
+  geoms << qMakePair( QString( "LINESTRING(0 0, 1 0, 1 1, 0 0)" ), true );  // may be closed (linear ring)
+  geoms << qMakePair( QString( "LINESTRING(0 0, 1 0, 1 1, 0 -1)" ), false ); // self-intersection
+  geoms << qMakePair( QString( "LINESTRING(0 0, 1 0, 1 1, 0.5 0, 0 1)" ), false ); // self-tangency
+  geoms << qMakePair( QString( "POINT(1 1)" ), true ); // points are simple
+  geoms << qMakePair( QString( "POLYGON((0 0, 1 1, 1 1, 0 0))" ), true ); // polygons are always simple, even if they are invalid
+  geoms << qMakePair( QString( "MULTIPOINT((1 1), (2 2))" ), true );
+  geoms << qMakePair( QString( "MULTIPOINT((1 1), (1 1))" ), false );  // must not contain the same point twice
+  geoms << qMakePair( QString( "MULTILINESTRING((0 0, 1 0), (0 1, 1 1))" ), true );
+  geoms << qMakePair( QString( "MULTILINESTRING((0 0, 1 0), (0 0, 1 0))" ), true );  // may be touching at endpoints
+  geoms << qMakePair( QString( "MULTILINESTRING((0 0, 1 1), (0 1, 1 0))" ), false );  // must not intersect each other
+  geoms << qMakePair( QString( "MULTIPOLYGON(((0 0, 1 1, 1 1, 0 0)),((0 0, 1 1, 1 1, 0 0)))" ), true ); // multi-polygons are always simple
+
+  Q_FOREACH ( const InputWktAndExpectedResult &pair, geoms )
+  {
+    QgsGeometry gInput = QgsGeometry::fromWkt( pair.first );
+    QVERIFY( !gInput.isNull() );
+
+    bool res = gInput.isSimple();
+    QCOMPARE( res, pair.second );
+  }
+}
+
 QGSTEST_MAIN( TestQgsGeometry )
 #include "testqgsgeometry.moc"