[FEATURE] pole_of_inaccessibility expression function

Exposes calculation of pole of inaccessiblity to expression engine
qgis · Nov 14, 2016 · 1f81a7c · 1f81a7c · nirvn · Nov 15, 2016
1 parent 880647e
commit 1f81a7c
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diff --git a/resources/function_help/json/pole_of_inaccessibility b/resources/function_help/json/pole_of_inaccessibility
@@ -0,0 +1,8 @@
+{
+  "name": "pole_of_inaccessibility",
+  "type": "function",
+  "description": "Calculates the approximate pole of inaccessibility for a surface, which is the most distant internal point from the boundary of the surface. This function uses the 'polylabel' algorithm (Vladimir Agafonkin, 2016), which is an iterative approach guaranteed to find the true pole of inaccessibility within a specified tolerance. More precise tolerances require more iterations and will take longer to calculate.",
+  "arguments": [ {"arg":"geometry","description":"a geometry"},
+                 {"arg":"tolerance","description":"maximum distance between the returned point and the true pole location"}],
+  "examples": [ { "expression":"geom_to_wkt(pole_of_inaccessibility( geom_from_wkt('POLYGON((0 1,0 9,3 10,3 3, 10 3, 10 1, 0 1))'), 0.1))", "returns":"Point(1.55, 1.55)"}]
+}
diff --git a/src/core/qgsexpression.cpp b/src/core/qgsexpression.cpp
@@ -2582,6 +2582,16 @@ static QVariant fcnPointOnSurface( const QVariantList& values, const QgsExpressi
   QVariant result = !geom.isEmpty() ? QVariant::fromValue( geom ) : QVariant();
   return result;
 }
+
+static QVariant fcnPoleOfInaccessibility( const QVariantList& values, const QgsExpressionContext*, QgsExpression* parent )
+{
+  QgsGeometry fGeom = getGeometry( values.at( 0 ), parent );
+  double tolerance = getDoubleValue( values.at( 1 ), parent );
+  QgsGeometry geom = fGeom.poleOfInaccessibility( tolerance );
+  QVariant result = !geom.isEmpty() ? QVariant::fromValue( geom ) : QVariant();
+  return result;
+}
+
 static QVariant fcnConvexHull( const QVariantList& values, const QgsExpressionContext*, QgsExpression* parent )
 {
   QgsGeometry fGeom = getGeometry( values.at( 0 ), parent );
@@ -3919,6 +3929,8 @@ const QList<QgsExpression::Function*>& QgsExpression::Functions()
                            fcnExtend, QStringLiteral( "GeometryGroup" ) )
     << new StaticFunction( QStringLiteral( "centroid" ), 1, fcnCentroid, QStringLiteral( "GeometryGroup" ) )
     << new StaticFunction( QStringLiteral( "point_on_surface" ), 1, fcnPointOnSurface, QStringLiteral( "GeometryGroup" ) )
+    << new StaticFunction( QStringLiteral( "pole_of_inaccessibility" ), ParameterList() << Parameter( QStringLiteral( "geometry" ) )
+                           << Parameter( QStringLiteral( "tolerance" ) ), fcnPoleOfInaccessibility, QStringLiteral( "GeometryGroup" ) )
     << new StaticFunction( QStringLiteral( "reverse" ), 1, fcnReverse, QStringLiteral( "GeometryGroup" ) )
     << new StaticFunction( QStringLiteral( "exterior_ring" ), 1, fcnExteriorRing, QStringLiteral( "GeometryGroup" ) )
     << new StaticFunction( QStringLiteral( "interior_ring_n" ), 2, fcnInteriorRingN, QStringLiteral( "GeometryGroup" ) )

diff --git a/tests/src/core/testqgsexpression.cpp b/tests/src/core/testqgsexpression.cpp
@@ -733,6 +733,11 @@ class TestQgsExpression: public QObject
       QTest::newRow( "point on surface line" ) << "geom_to_wkt(point_on_surface( geomFromWKT('LINESTRING (-1 2, 9 12)') ))" << false << QVariant( "Point (-1 2)" );
       QTest::newRow( "point on surface not geom" ) << "point_on_surface('g')" << true << QVariant();
       QTest::newRow( "point on surface null" ) << "point_on_surface(NULL)" << false << QVariant();
+      QTest::newRow( "pole_of_inaccessibility polygon" ) << "round(x(pole_of_inaccessibility( geomFromWKT('POLYGON((0 1,0 9,3 10,3 3, 10 3, 10 1, 0 1))'), 0.1))*100)" << false << QVariant( 155 );
+      QTest::newRow( "pole_of_inaccessibility polygon" ) << "round(y(pole_of_inaccessibility( geomFromWKT('POLYGON((0 1,0 9,3 10,3 3, 10 3, 10 1, 0 1))'), 0.1))*100)" << false << QVariant( 255 );
+      QTest::newRow( "pole_of_inaccessibility not poly" ) << "geom_to_wkt(pole_of_inaccessibility( geomFromWKT('POINT (1.5 0.5)'), 0.1 ))" << false << QVariant();
+      QTest::newRow( "pole_of_inaccessibility not geom" ) << "pole_of_inaccessibility('g',0.1)" << true << QVariant();
+      QTest::newRow( "pole_of_inaccessibility null" ) << "pole_of_inaccessibility(NULL,0.1)" << false << QVariant();
       QTest::newRow( "is_closed not geom" ) << "is_closed('g')" << true << QVariant();
       QTest::newRow( "is_closed null" ) << "is_closed(NULL)" << false << QVariant();
       QTest::newRow( "is_closed point" ) << "is_closed(geom_from_wkt('POINT(1 2)'))" << false << QVariant();