qgsalgorithmconcavehullbyfeature.cpp

Go to the documentation of this file.

/***************************************************************************
                         qgsalgorithmconcavehullbyfeature.cpp
                         ---------------------
    begin                : May 2025
    copyright            : (C) 2025 by Nyall Dawson
    email                : nyall dot dawson at gmail dot com
 ***************************************************************************/
 
/***************************************************************************
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 ***************************************************************************/
 
#include "qgsalgorithmconcavehullbyfeature.h"
 
#include "qgsgeometrycollection.h"
#include "qgsgeos.h"
 
#include <QString>
 
using namespace Qt::StringLiterals;

 
QString QgsConcaveHullByFeatureAlgorithm::name() const
{
  return u"concavehullbyfeature"_s;
}
 
QString QgsConcaveHullByFeatureAlgorithm::displayName() const
{
  return QObject::tr( "Concave hull (by feature)" );
}
 
QStringList QgsConcaveHullByFeatureAlgorithm::tags() const
{
  return QObject::tr( "concave,hull,bounds,bounding,convex" ).split( ',' );
}
 
QString QgsConcaveHullByFeatureAlgorithm::group() const
{
  return QObject::tr( "Vector geometry" );
}
 
QString QgsConcaveHullByFeatureAlgorithm::groupId() const
{
  return u"vectorgeometry"_s;
}
 
QString QgsConcaveHullByFeatureAlgorithm::outputName() const
{
  return QObject::tr( "Concave hulls" );
}
 
QString QgsConcaveHullByFeatureAlgorithm::shortHelpString() const
{
  return QObject::tr( "This algorithm calculates the concave hull for each feature in an input layer." )
         + u"\n\n"_s
         + QObject::tr( "For point and line layers, a concave hull is a polygon which contains all the vertices of the input geometries, but is a better approximation than the convex hull to the area occupied by the input." )
         + u"\n\n"_s
         + QObject::tr(
           "When the input is a polygon layer, the algorithm operates differently: it computes a concave hull that respects the interior of the input polygons. The concave hull does not intersect "
           "the polygon interiors. The computed hull also fills the empty space between the polygons within a multi-polygon feature."
         )
         + u"\n\n"_s
         + QObject::tr( "See the 'Concave hull (by layer)' algorithm for a concave hull calculation which covers the whole layer or grouped subsets of features." );
}
 
QString QgsConcaveHullByFeatureAlgorithm::shortDescription() const
{
  return QObject::tr( "Calculates the concave hull for each feature in an input layer." );
}
 
QgsConcaveHullByFeatureAlgorithm *QgsConcaveHullByFeatureAlgorithm::createInstance() const
{
  return new QgsConcaveHullByFeatureAlgorithm();
}
 
void QgsConcaveHullByFeatureAlgorithm::initParameters( const QVariantMap & )
{
  auto alphaParam
    = std::make_unique<QgsProcessingParameterNumber>( u"ALPHA"_s, QObject::tr( "Threshold (0-1, where 1 is equivalent with Convex Hull)" ), Qgis::ProcessingNumberParameterType::Double, 0.3, false, 0, 1 );
  alphaParam->setHelp(
    QObject::tr(
      "Controls the concaveness of the computed hull. A value of 1 produces the convex hull, while a value closer to 0 produces a highly concave hull. For point and line layers, this value "
      "represents the target percentage of the convex hull area. For polygon layers, it specifies the maximum edge length as a fraction of the difference between the longest and shortest edge "
      "lengths in the empty space between polygons."
    )
  );
  addParameter( alphaParam.release() );
 
  auto holesParam = std::make_unique<QgsProcessingParameterBoolean>( u"HOLES"_s, QObject::tr( "Allow holes" ), true );
  holesParam->setHelp( QObject::tr( "Controls whether the computed concave hull is allowed to contain holes." ) );
  addParameter( holesParam.release() );
}
 
QList<int> QgsConcaveHullByFeatureAlgorithm::inputLayerTypes() const
{
  return QList<int>() << static_cast<int>( Qgis::ProcessingSourceType::VectorPoint ) << static_cast<int>( Qgis::ProcessingSourceType::VectorLine ) << static_cast<int>( Qgis::ProcessingSourceType::VectorPolygon );
}
 
QgsFields QgsConcaveHullByFeatureAlgorithm::outputFields( const QgsFields &inputFields ) const
{
  QgsFields newFields;
  newFields.append( QgsField( u"area"_s, QMetaType::Type::Double, QString(), 20, 6 ) );
  newFields.append( QgsField( u"perimeter"_s, QMetaType::Type::Double, QString(), 20, 6 ) );
  return QgsProcessingUtils::combineFields( inputFields, newFields );
}
 
bool QgsConcaveHullByFeatureAlgorithm::prepareAlgorithm( const QVariantMap &parameters, QgsProcessingContext &context, QgsProcessingFeedback * )
{
#if GEOS_VERSION_NUM < GEOS_COMPUTE_VERSION( 3, 11, 0 )
  throw QgsProcessingException( QObject::tr( "This algorithm requires a QGIS build based on GEOS 3.11 or later" ) );
#endif
  mPercentage = parameterAsDouble( parameters, u"ALPHA"_s, context );
  mAllowHoles = parameterAsBool( parameters, u"HOLES"_s, context );
  return true;
}
 
QgsFeatureList QgsConcaveHullByFeatureAlgorithm::processFeature( const QgsFeature &feature, QgsProcessingContext &, QgsProcessingFeedback *feedback )
{
  QGS_MARK_ALGORITHM_SOURCE
 
  QgsFeature f = feature;
  if ( f.hasGeometry() )
  {
    QgsGeometry outputGeometry;
    if ( f.geometry().type() == Qgis::GeometryType::Point )
    {
      const QgsAbstractGeometry *inputGeometry = f.geometry().constGet();
      const QgsGeometryCollection *collection = qgsgeometry_cast< const QgsGeometryCollection * >( inputGeometry );
      if ( !collection || collection->numGeometries() == 1 )
      {
        feedback->reportError( QObject::tr( "Cannot calculate concave hull for a single point feature (%1) (try 'Concave hull (by layer)' algorithm instead)." ).arg( f.id() ) );
        f.clearGeometry();
      }
      else
      {
        outputGeometry = f.geometry().concaveHull( mPercentage, mAllowHoles );
        if ( outputGeometry.isNull() && !outputGeometry.lastError().isEmpty() )
          feedback->reportError( outputGeometry.lastError() );
        f.setGeometry( outputGeometry );
      }
    }
    else if ( f.geometry().type() == Qgis::GeometryType::Line )
    {
      outputGeometry = f.geometry().concaveHull( mPercentage, mAllowHoles );
      if ( outputGeometry.isNull() && !outputGeometry.lastError().isEmpty() )
        feedback->reportError( outputGeometry.lastError() );
      f.setGeometry( outputGeometry );
    }
    else if ( f.geometry().type() == Qgis::GeometryType::Polygon )
    {
      outputGeometry = f.geometry().concaveHullOfPolygons( mPercentage, mAllowHoles );
      if ( outputGeometry.isNull() && !outputGeometry.lastError().isEmpty() )
        feedback->reportError( outputGeometry.lastError() );
      f.setGeometry( outputGeometry );
    }
 
    if ( outputGeometry.type() == Qgis::GeometryType::Polygon )
    {
      QgsAttributes attrs = f.attributes();
      attrs << outputGeometry.constGet()->area() << outputGeometry.constGet()->perimeter();
      f.setAttributes( attrs );
    }
    else
    {
      if ( outputGeometry.type() == Qgis::GeometryType::Line )
      {
        feedback->pushWarning( QObject::tr( "Concave hull for feature %1 resulted in a linestring, ignoring" ).arg( f.id() ) );
      }
      else if ( outputGeometry.type() == Qgis::GeometryType::Point )
      {
        feedback->pushWarning( QObject::tr( "Concave hull for feature %1 resulted in a point, ignoring" ).arg( f.id() ) );
      }
      QgsAttributes attrs = f.attributes();
      attrs << QVariant() << QVariant();
      f.setAttributes( attrs );
    }
  }
  return QgsFeatureList() << f;
}