qgsalgorithmcoveragesimplify.cpp

Go to the documentation of this file.

/***************************************************************************
                         qgsalgorithmcoveragesimplify.cpp
                         ---------------------
    begin                : October 2023
    copyright            : (C) 2023 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 "qgsalgorithmcoveragesimplify.h"
#include "qgsgeometrycollection.h"
#include "qgsgeos.h"
 
 
 
QString QgsCoverageSimplifyAlgorithm::name() const
{
  return QStringLiteral( "coveragesimplify" );
}
 
QString QgsCoverageSimplifyAlgorithm::displayName() const
{
  return QObject::tr( "Simplify coverage" );
}
 
QStringList QgsCoverageSimplifyAlgorithm::tags() const
{
  return QObject::tr( "topological,boundary" ).split( ',' );
}
 
QString QgsCoverageSimplifyAlgorithm::group() const
{
  return QObject::tr( "Vector coverage" );
}
 
QString QgsCoverageSimplifyAlgorithm::groupId() const
{
  return QStringLiteral( "vectorcoverage" );
}
 
void QgsCoverageSimplifyAlgorithm::initAlgorithm( const QVariantMap & )
{
  addParameter( new QgsProcessingParameterFeatureSource( QStringLiteral( "INPUT" ), QObject::tr( "Input layer" ), QList<int>() << static_cast<int>( Qgis::ProcessingSourceType::VectorPolygon ) ) );
  addParameter( new QgsProcessingParameterDistance( QStringLiteral( "TOLERANCE" ), QObject::tr( "Tolerance" ), 1.0, QStringLiteral( "INPUT" ), false, 0, 10000000.0 ) );
  auto boundaryParameter = std::make_unique<QgsProcessingParameterBoolean>( QStringLiteral( "PRESERVE_BOUNDARY" ), QObject::tr( "Preserve boundary" ), false );
  boundaryParameter->setHelp( QObject::tr( "When enabled the outside edges of the coverage will be preserved without simplification." ) );
  addParameter( boundaryParameter.release() );
 
  addParameter( new QgsProcessingParameterFeatureSink( QStringLiteral( "OUTPUT" ), QObject::tr( "Simplified" ), Qgis::ProcessingSourceType::VectorPolygon ) );
}
 
QString QgsCoverageSimplifyAlgorithm::shortDescription() const
{
  return QObject::tr( "Simplifies a coverage of polygon features while retaining valid coverage." );
}
 
QString QgsCoverageSimplifyAlgorithm::shortHelpString() const
{
  return QObject::tr( "This algorithm operates on a coverage (represented as a set of polygon features "
                      "with exactly matching edge geometry) to apply a Visvalingam–Whyatt "
                      "simplification to the edges, reducing complexity in proportion with "
                      "the provided tolerance, while retaining a valid coverage (i.e. no edges "
                      "will cross or touch after the simplification).\n\n"
                      "Geometries will never be removed, but they may be simplified down to just "
                      "a triangle. Also, some geometries (such as polygons which have too "
                      "few non-repeated points) will be returned unchanged.\n\n"
                      "If the input dataset is not a valid coverage due to overlaps, "
                      "it will still be simplified, but invalid topology such as crossing "
                      "edges will still be invalid." );
}
 
QgsCoverageSimplifyAlgorithm *QgsCoverageSimplifyAlgorithm::createInstance() const
{
  return new QgsCoverageSimplifyAlgorithm();
}
 
QVariantMap QgsCoverageSimplifyAlgorithm::processAlgorithm( const QVariantMap &parameters, QgsProcessingContext &context, QgsProcessingFeedback *feedback )
{
  std::unique_ptr<QgsProcessingFeatureSource> source( parameterAsSource( parameters, QStringLiteral( "INPUT" ), context ) );
  if ( !source )
    throw QgsProcessingException( invalidSourceError( parameters, QStringLiteral( "INPUT" ) ) );
 
  const bool preserveBoundary = parameterAsBoolean( parameters, QStringLiteral( "PRESERVE_BOUNDARY" ), context );
  const double tolerance = parameterAsDouble( parameters, QStringLiteral( "TOLERANCE" ), context );
 
  QString sinkId;
  std::unique_ptr<QgsFeatureSink> sink( parameterAsSink( parameters, QStringLiteral( "OUTPUT" ), context, sinkId, source->fields(), source->wkbType(), source->sourceCrs() ) );
  if ( !sink )
    throw QgsProcessingException( invalidSinkError( parameters, QStringLiteral( "OUTPUT" ) ) );
 
  // we have no choice but to build up a list of features in advance
  QVector<QgsFeature> featuresWithGeom;
  QVector<QgsFeature> featuresWithoutGeom;
  QgsGeometryCollection collection;
 
  const long count = source->featureCount();
  if ( count > 0 )
  {
    featuresWithGeom.reserve( count );
    collection.reserve( count );
  }
 
  const double step = count > 0 ? 100.0 / count : 1;
  int current = 0;
 
  feedback->pushInfo( QObject::tr( "Collecting features" ) );
 
  QgsFeature inFeature;
  QgsFeatureIterator features = source->getFeatures();
  while ( features.nextFeature( inFeature ) )
  {
    if ( feedback->isCanceled() )
    {
      break;
    }
 
    if ( inFeature.hasGeometry() )
    {
      featuresWithGeom.append( inFeature );
      collection.addGeometry( inFeature.geometry().constGet()->clone() );
    }
    else
    {
      featuresWithoutGeom.append( inFeature );
    }
 
 
    feedback->setProgress( current * step * 0.2 );
    current++;
  }
 
  QString error;
  QgsGeos geos( &collection );
  switch ( source->invalidGeometryCheck() )
  {
    case Qgis::InvalidGeometryCheck::NoCheck:
      break;
 
    case Qgis::InvalidGeometryCheck::SkipInvalid:
    case Qgis::InvalidGeometryCheck::AbortOnInvalid:
    {
      if ( geos.validateCoverage( 0, nullptr, &error ) != Qgis::CoverageValidityResult::Valid )
      {
        throw QgsProcessingException( QObject::tr( "Coverage is not valid" ) );
      }
      break;
    }
  }
 
  feedback->pushInfo( QObject::tr( "Simplifying coverage" ) );
 
  std::unique_ptr<QgsAbstractGeometry> simplified;
  try
  {
    simplified = geos.simplifyCoverageVW( tolerance, preserveBoundary, &error );
  }
  catch ( QgsNotSupportedException &e )
  {
    throw QgsProcessingException( e.what() );
  }
 
  if ( !simplified )
  {
    if ( !error.isEmpty() )
      throw QgsProcessingException( error );
    else
      throw QgsProcessingException( QObject::tr( "No geometry was returned for simplified coverage" ) );
  }
 
  feedback->setProgress( 80 );
 
  feedback->pushInfo( QObject::tr( "Storing features" ) );
  long long featureIndex = 0;
  for ( auto partsIt = simplified->const_parts_begin(); partsIt != simplified->const_parts_end(); ++partsIt )
  {
    QgsFeature outFeature = featuresWithGeom.value( featureIndex );
    outFeature.setGeometry( QgsGeometry( *partsIt ? ( *partsIt )->clone() : nullptr ) );
    if ( !sink->addFeature( outFeature, QgsFeatureSink::FastInsert ) )
      throw QgsProcessingException( writeFeatureError( sink.get(), parameters, QStringLiteral( "OUTPUT" ) ) );
 
 
    feedback->setProgress( featureIndex * step * 0.2 + 80 );
    featureIndex++;
  }
  for ( const QgsFeature &feature : featuresWithoutGeom )
  {
    QgsFeature outFeature = feature;
    if ( !sink->addFeature( outFeature, QgsFeatureSink::FastInsert ) )
      throw QgsProcessingException( writeFeatureError( sink.get(), parameters, QStringLiteral( "OUTPUT" ) ) );
  }
 
  sink->finalize();
 
  QVariantMap outputs;
  outputs.insert( QStringLiteral( "OUTPUT" ), sinkId );
  return outputs;
}