[FEATURE] New expression functions for angle/distance interpolation

angle_at_vertex: returns average (bisector) angle to a geometry
at a specified vertex index
distance_to_vertex: returns distance along geometry to a specified
vertex index
line_interpolate_angle: calculates the angle parallel to a geometry
at the specified distance along the geometry

Sponsored by Andreas Neumann

resources/function_help/json/angle_at_vertex

@@ -0,0 +1,8 @@
+{
+  "name": "angle_at_vertex",
+  "type": "function",
+  "description": "Returns the bisector angle (average angle) to the geometry for a specified vertex on a linestring geometry. Angles are in degrees clockwise from north.",
+  "arguments": [ {"arg":"geometry","description":"a linestring geometry"},
+                 {"arg":"vertex","description":"vertex index, starting from 0"}],
+  "examples": [ { "expression":"angle_at_vertex(geometry:=geom_from_wkt('LineString(0 0, 10 0, 10 10)'),vertex:=1)", "returns":"45.0"}]
+}

resources/function_help/json/distance_to_vertex

@@ -0,0 +1,8 @@
+{
+  "name": "distance_to_vertex",
+  "type": "function",
+  "description": "Returns the distance along the geometry to a specified vertex.",
+  "arguments": [ {"arg":"geometry","description":"a linestring geometry"},
+                 {"arg":"vertex","description":"vertex index, starting from 0"}],
+  "examples": [ { "expression":"distance_to_vertex(geometry:=geom_from_wkt('LineString(0 0, 10 0, 10 10)'),vertex:=1)", "returns":"10.0"}]
+}

resources/function_help/json/line_interpolate_angle

@@ -0,0 +1,8 @@
+{
+  "name": "line_interpolate_angle",
+  "type": "function",
+  "description": "Returns the angle parallel to the geometry at a specified distance along a linestring geometry. Angles are in degrees clockwise from north.",
+  "arguments": [ {"arg":"geometry","description":"a linestring geometry"},
+                 {"arg":"distance","description":"distance along line to interpolate angle at"}],
+  "examples": [ { "expression":"line_interpolate_angle(geometry:=geom_from_wkt('LineString(0 0, 10 0)'),distance:=5)", "returns":"90.0"}]
+}

src/core/qgsexpression.cpp

@@ -2559,6 +2559,30 @@ static QVariant fcnLineInterpolatePoint( const QVariantList& values, const QgsEx
   return result;
 }
 
+static QVariant fcnLineInterpolateAngle( const QVariantList& values, const QgsExpressionContext*, QgsExpression* parent )
+{
+  QgsGeometry lineGeom = getGeometry( values.at( 0 ), parent );
+  double distance = getDoubleValue( values.at( 1 ), parent );
+
+  return lineGeom.interpolateAngle( distance ) * 180.0 / M_PI;
+}
+
+static QVariant fcnAngleAtVertex( const QVariantList& values, const QgsExpressionContext*, QgsExpression* parent )
+{
+  QgsGeometry geom = getGeometry( values.at( 0 ), parent );
+  int vertex = getIntValue( values.at( 1 ), parent );
+
+  return geom.angleAtVertex( vertex ) * 180.0 / M_PI;
+}
+
+static QVariant fcnDistanceToVertex( const QVariantList& values, const QgsExpressionContext*, QgsExpression* parent )
+{
+  QgsGeometry geom = getGeometry( values.at( 0 ), parent );
+  int vertex = getIntValue( values.at( 1 ), parent );
+
+  return geom.distanceToVertex( vertex );
+}
+
 static QVariant fcnLineLocatePoint( const QVariantList& values, const QgsExpressionContext*, QgsExpression* parent )
 {
   QgsGeometry lineGeom = getGeometry( values.at( 0 ), parent );
@@ -3148,6 +3172,7 @@ const QStringList& QgsExpression::BuiltinFunctions()
     << "distance" << "intersection" << "sym_difference" << "combine"
     << "extrude" << "azimuth" <<  "project" << "closest_point" << "shortest_line"
     << "line_locate_point" << "line_interpolate_point"
+    << "line_interpolate_angle" << "angle_at_vertex" << "distance_to_vertex"
     << "union" << "geom_to_wkt" << "geomToWKT" << "geometry"
     << "transform" << "get_feature" << "getFeature"
     << "levenshtein" << "longest_common_substring" << "hamming_distance"
@@ -3375,8 +3400,14 @@ const QList<QgsExpression::Function*>& QgsExpression::Functions()
     << new StaticFunction( "shortest_line", 2, fcnShortestLine, "GeometryGroup" )
     << new StaticFunction( "line_interpolate_point", ParameterList() << Parameter( "geometry" )
                            << Parameter( "distance" ), fcnLineInterpolatePoint, "GeometryGroup" )
+    << new StaticFunction( "line_interpolate_angle", ParameterList() << Parameter( "geometry" )
+                           << Parameter( "distance" ), fcnLineInterpolateAngle, "GeometryGroup" )
     << new StaticFunction( "line_locate_point", ParameterList() << Parameter( "geometry" )
                            << Parameter( "point" ), fcnLineLocatePoint, "GeometryGroup" )
+    << new StaticFunction( "angle_at_vertex", ParameterList() << Parameter( "geometry" )
+                           << Parameter( "vertex" ), fcnAngleAtVertex, "GeometryGroup" )
+    << new StaticFunction( "distance_to_vertex", ParameterList() << Parameter( "geometry" )
+                           << Parameter( "vertex" ), fcnDistanceToVertex, "GeometryGroup" )
     << new StaticFunction( "$id", 0, fcnFeatureId, "Record" )
     << new StaticFunction( "$currentfeature", 0, fcnFeature, "Record" )
     << new StaticFunction( "uuid", 0, fcnUuid, "Record", QString(), false, QStringList(), false, QStringList() << "$uuid" )

tests/src/core/testqgsexpression.cpp

@@ -786,6 +786,18 @@ class TestQgsExpression: public QObject
       QTest::newRow( "line_locate_point null" ) << "line_locate_point(NULL, geom_from_wkt('Point 5 0'))" << false << QVariant();
       QTest::newRow( "line_locate_point point" ) << "line_locate_point(geom_from_wkt('POINT(1 2)'),geom_from_wkt('Point 5 0'))" << false << QVariant();
       QTest::newRow( "line_locate_point line" ) << "line_locate_point(geometry:=geom_from_wkt('LineString(0 0, 10 0)'),point:=geom_from_wkt('Point(5 0)'))" << false << QVariant( 5.0 );
+      QTest::newRow( "line_interpolate_angle not geom" ) << "line_interpolate_angle('g', 5)" << true << QVariant();
+      QTest::newRow( "line_interpolate_angle null" ) << "line_interpolate_angle(NULL, 5)" << false << QVariant();
+      QTest::newRow( "line_interpolate_angle point" ) << "line_interpolate_angle(geom_from_wkt('POINT(1 2)'),5)" << false << QVariant( 0.0 );
+      QTest::newRow( "line_interpolate_angle line" ) << "line_interpolate_angle(geometry:=geom_from_wkt('LineString(0 0, 10 0)'),distance:=5)" << false << QVariant( 90.0 );
+      QTest::newRow( "angle_at_vertex not geom" ) << "angle_at_vertex('g', 5)" << true << QVariant();
+      QTest::newRow( "angle_at_vertex null" ) << "angle_at_vertex(NULL, 0)" << false << QVariant();
+      QTest::newRow( "angle_at_vertex point" ) << "angle_at_vertex(geom_from_wkt('POINT(1 2)'),0)" << false << QVariant( 0.0 );
+      QTest::newRow( "angle_at_vertex line" ) << "angle_at_vertex(geometry:=geom_from_wkt('LineString(0 0, 10 0, 10 10)'),vertex:=1)" << false << QVariant( 45.0 );
+      QTest::newRow( "distance_to_vertex not geom" ) << "distance_to_vertex('g', 5)" << true << QVariant();
+      QTest::newRow( "distance_to_vertex null" ) << "distance_to_vertex(NULL, 0)" << false << QVariant();
+      QTest::newRow( "distance_to_vertex point" ) << "distance_to_vertex(geom_from_wkt('POINT(1 2)'),0)" << false << QVariant( 0.0 );
+      QTest::newRow( "distance_to_vertex line" ) << "distance_to_vertex(geometry:=geom_from_wkt('LineString(0 0, 10 0, 10 10)'),vertex:=1)" << false << QVariant( 10.0 );
 
       // string functions
       QTest::newRow( "lower" ) << "lower('HeLLo')" << false << QVariant( "hello" );