Better error location for missing vertex errors

When showing a missing vertex error, the map canvas is now centered on the missing vertex
location and scaled by taking neighbouring vertices into account.

src/analysis/vector/geometry_checker/qgsgeometrymissingvertexcheck.cpp

@@ -135,7 +135,7 @@ void QgsGeometryMissingVertexCheck::processPolygon( const QgsCurvePolygon *polyg
   const int numRings = polygon->numInteriorRings();
   for ( int i = 0; i < numRings; ++i )
   {
-    geomEngine = QgsGeometryCheckerUtils::createGeomEngine( polygon->exteriorRing(), mContext->tolerance );
+    geomEngine = QgsGeometryCheckerUtils::createGeomEngine( polygon->interiorRing( i ), mContext->tolerance );
     boundaries->addGeometry( geomEngine->buffer( mContext->tolerance, 5 ) );
   }
 
@@ -177,14 +177,36 @@ void QgsGeometryMissingVertexCheck::processPolygon( const QgsCurvePolygon *polyg
               }
             }
             if ( !alreadyReported )
-              errors.append( new QgsGeometryCheckError( this, layerFeature, QgsPointXY( pt ) ) );
+            {
+              std::unique_ptr<QgsGeometryMissingVertexCheckError> error = qgis::make_unique<QgsGeometryMissingVertexCheckError>( this, layerFeature, QgsPointXY( pt ) );
+              error->setAffectedAreaBBox( contextBoundingBox( polygon, vertexId, pt ) );
+
+              errors.append( error.release() );
+            }
           }
         }
       }
     }
   }
 }
 
+QgsRectangle QgsGeometryMissingVertexCheck::contextBoundingBox( const QgsCurvePolygon *polygon, const QgsVertexId &vertexId, const QgsPoint &point ) const
+{
+  QgsVertexId vertexBefore;
+  QgsVertexId vertexAfter;
+
+  polygon->adjacentVertices( vertexId, vertexBefore, vertexAfter );
+
+  QgsPoint ptBefore = polygon->vertexAt( vertexBefore );
+  QgsPoint ptAt = polygon->vertexAt( vertexId );
+  QgsPoint ptAfter = polygon->vertexAt( vertexAfter );
+
+  double length = std::abs( ptAt.distance( ptBefore ) ) + std::abs( ptAt.distance( ptAfter ) );
+
+  QgsRectangle rect( point.x() - length / 2, point.y() - length / 2, point.x() + length / 2, point.y() + length / 2 );
+  return rect;
+}
+
 QString QgsGeometryMissingVertexCheck::id() const
 {
   return factoryId();
@@ -236,3 +258,18 @@ QgsGeometryCheck::CheckType QgsGeometryMissingVertexCheck::factoryCheckType()
   return QgsGeometryCheck::LayerCheck;
 }
 ///@endcond private
+
+QgsGeometryMissingVertexCheckError::QgsGeometryMissingVertexCheckError( const QgsGeometryCheck *check, const QgsGeometryCheckerUtils::LayerFeature &layerFeature, const QgsPointXY &errorLocation, QgsVertexId vidx, const QVariant &value, QgsGeometryCheckError::ValueType valueType )
+  : QgsGeometryCheckError( check, layerFeature, errorLocation, vidx, value, valueType )
+{
+}
+
+QgsRectangle QgsGeometryMissingVertexCheckError::affectedAreaBBox() const
+{
+  return mAffectedAreaBBox;
+}
+
+void QgsGeometryMissingVertexCheckError::setAffectedAreaBBox( const QgsRectangle &affectedAreaBBox )
+{
+  mAffectedAreaBBox = affectedAreaBBox;
+}

src/analysis/vector/geometry_checker/qgsgeometrymissingvertexcheck.h

@@ -23,6 +23,43 @@
 
 class QgsCurvePolygon;
 
+/**
+ * \ingroup analysis
+ *
+ * A geometry check error for a missing vertex.
+ * Includes additional details about the bounding box of the error,
+ * centered on the missing error location and scaled by taking neighbouring
+ * vertices into account.
+ *
+ * \since QGIS 3.8
+ */
+class ANALYSIS_EXPORT QgsGeometryMissingVertexCheckError : public QgsGeometryCheckError
+{
+  public:
+
+    /**
+     * Create a new missing vertex check error.
+     */
+    QgsGeometryMissingVertexCheckError( const QgsGeometryCheck *check,
+                                        const QgsGeometryCheckerUtils::LayerFeature &layerFeature,
+                                        const QgsPointXY &errorLocation,
+                                        QgsVertexId vidx = QgsVertexId(),
+                                        const QVariant &value = QVariant(),
+                                        ValueType valueType = ValueOther );
+
+    QgsRectangle affectedAreaBBox() const override;
+
+    /**
+     * Set the bounding box of the affected area.
+     *
+     * \since QGIS 3.8
+     */
+    void setAffectedAreaBBox( const QgsRectangle &affectedAreaBBox );
+
+  private:
+    QgsRectangle mAffectedAreaBBox;
+};
+
 /**
  * \ingroup analysis
  *
@@ -73,6 +110,8 @@ class ANALYSIS_EXPORT QgsGeometryMissingVertexCheck : public QgsGeometryCheck
 
   private:
     void processPolygon( const QgsCurvePolygon *polygon, QgsFeaturePool *featurePool, QList<QgsGeometryCheckError *> &errors, const QgsGeometryCheckerUtils::LayerFeature &layerFeature, QgsFeedback *feedback ) const;
+
+    QgsRectangle contextBoundingBox( const QgsCurvePolygon *polygon, const QgsVertexId &vertexId, const QgsPoint &point ) const;
 };