nearest point measure in identify tool

Author: blazek

python/core/geometry/qgsgeometryutils.sip

@@ -37,6 +37,12 @@ class QgsGeometryUtils
  :rtype: QgsPoint
 %End
 
+    static double closestPointMeasure( const QgsAbstractGeometry &geom, const QgsPoint &pt );
+%Docstring
+ Returns measure of nearest point on a geometry for a specified point or NaN if geometry does not have measures
+ :rtype: float
+%End
+
     static double distanceToVertex( const QgsAbstractGeometry &geom, QgsVertexId id );
 %Docstring
  Returns the distance along a geometry from its first vertex to the specified vertex.

src/core/geometry/qgsgeometryutils.cpp

@@ -93,6 +93,35 @@ QgsPoint QgsGeometryUtils::closestVertex( const QgsAbstractGeometry &geom, const
   return minDistPoint;
 }
 
+double QgsGeometryUtils::closestPointMeasure( const QgsAbstractGeometry &geom, const QgsPoint &pt )
+{
+  if ( QgsWkbTypes::hasM( geom.wkbType() ) )
+  {
+    QgsPoint closestPoint;
+    QgsVertexId vertexAfter;
+    bool leftOf;
+    geom.closestSegment( pt, closestPoint, vertexAfter, &leftOf, DEFAULT_SEGMENT_EPSILON );
+    if ( vertexAfter.isValid() )
+    {
+      QgsPoint pointAfter = geom.vertexAt( vertexAfter );
+      if ( vertexAfter.vertex > 0 )
+      {
+        QgsVertexId vertexBefore = vertexAfter;
+        vertexBefore.vertex--;
+        QgsPoint pointBefore = geom.vertexAt( vertexBefore );
+        double length = pointBefore.distance( pointAfter );
+        double distance = pointBefore.distance( closestPoint );
+        return pointBefore.m() + ( pointAfter.m() - pointBefore.m() ) * distance / length;
+      }
+      else
+      {
+        return pointAfter.m();
+      }
+    }
+  }
+  return std::numeric_limits<double>::quiet_NaN();
+}
+
 double QgsGeometryUtils::distanceToVertex( const QgsAbstractGeometry &geom, QgsVertexId id )
 {
   double currentDist = 0;

src/core/geometry/qgsgeometryutils.h

@@ -44,6 +44,10 @@ class CORE_EXPORT QgsGeometryUtils
      */
     static QgsPoint closestVertex( const QgsAbstractGeometry &geom, const QgsPoint &pt, QgsVertexId &id SIP_OUT );
 
+    /** Returns measure of nearest point on a geometry for a specified point or NaN if geometry does not have measures
+     */
+    static double closestPointMeasure( const QgsAbstractGeometry &geom, const QgsPoint &pt );
+
     /** Returns the distance along a geometry from its first vertex to the specified vertex.
      * \param geom geometry
      * \param id vertex id to find distance to

src/gui/qgsmaptoolidentify.cpp

@@ -326,6 +326,18 @@ void QgsMapToolIdentify::closestVertexAttributes( const QgsAbstractGeometry &geo
   }
 }
 
+void QgsMapToolIdentify::closestPointAttributes( const QgsAbstractGeometry &geometry, QgsMapLayer *layer, const QgsPointXY &layerPoint, QMap< QString, QString > &derivedAttributes )
+{
+  Q_UNUSED( layer );
+  // measure
+  if ( QgsWkbTypes::hasM( geometry.wkbType() ) )
+  {
+    double measure = QgsGeometryUtils::closestPointMeasure( geometry, QgsPoint( layerPoint.x(), layerPoint.y() ) );
+    QString str = QLocale::system().toString( measure, 'g', 10 );
+    derivedAttributes.insert( QStringLiteral( "Closest point M" ), str );
+  }
+}
+
 QString QgsMapToolIdentify::formatCoordinate( const QgsPointXY &canvasPoint ) const
 {
   return QgsCoordinateUtils::formatCoordinateForProject( canvasPoint, mCanvas->mapSettings().destinationCrs(),
@@ -392,6 +404,7 @@ QMap< QString, QString > QgsMapToolIdentify::featureDerivedAttributes( QgsFeatur
 
       //add details of closest vertex to identify point
       closestVertexAttributes( *curve, vId, layer, derivedAttributes );
+      closestPointAttributes( *curve, layer, layerPoint, derivedAttributes );
 
       // Add the start and end points in as derived attributes
       QgsPointXY pnt = mCanvas->mapSettings().layerToMapCoordinates( layer, QgsPointXY( curve->startPoint().x(), curve->startPoint().y() ) );

src/gui/qgsmaptoolidentify.h

@@ -183,6 +183,10 @@ class GUI_EXPORT QgsMapToolIdentify : public QgsMapTool
      */
     void closestVertexAttributes( const QgsAbstractGeometry &geometry, QgsVertexId vId, QgsMapLayer *layer, QMap< QString, QString > &derivedAttributes );
 
+    /** Adds details of the closest point to derived attributes
+     */
+    void closestPointAttributes( const QgsAbstractGeometry &geometry, QgsMapLayer *layer, const QgsPointXY &layerPoint, QMap< QString, QString > &derivedAttributes );
+
     QString formatCoordinate( const QgsPointXY &canvasPoint ) const;
     QString formatXCoordinate( const QgsPointXY &canvasPoint ) const;
     QString formatYCoordinate( const QgsPointXY &canvasPoint ) const;