qgsmeshcontours.cpp

Go to the documentation of this file.

/***************************************************************************
                          qgsmeshcontours.cpp
                          -------------------
    begin                : September 25th, 2019
    copyright            : (C) 2018 by Peter Petrik
    email                : zilolv 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 "qgsmeshcontours.h"
 
#include <limits>
 
#include "qgsfeature.h"
#include "qgsfeedback.h"
#include "qgsgeometry.h"
#include "qgsgeometryutils.h"
#include "qgslinestring.h"
#include "qgsmapsettings.h"
#include "qgsmeshdataprovider.h"
#include "qgsmeshlayer.h"
#include "qgsmeshlayerutils.h"
#include "qgsmultilinestring.h"
#include "qgspoint.h"
#include "qgspolygon.h"
#include "qgsproject.h"
#include "qgstriangularmesh.h"
 
#include <QPair>
#include <QSet>
 
QgsMeshContours::QgsMeshContours( QgsMeshLayer *layer )
  : mMeshLayer( layer )
{
  if ( !mMeshLayer || !mMeshLayer->dataProvider() || !mMeshLayer->dataProvider()->isValid() )
    return;
 
  // Support for meshes with edges is not implemented
  if ( mMeshLayer->dataProvider()->contains( QgsMesh::ElementType::Edge ) )
    return;
 
  mMeshLayer->dataProvider()->populateMesh( &mNativeMesh );
  mTriangularMesh.update( &mNativeMesh );
}
 
QgsMeshContours::QgsMeshContours( const QgsTriangularMesh &triangularMesh, const QgsMesh &nativeMesh, const QVector<double> &datasetValues, const QgsMeshDataBlock scalarActiveFaceFlagValues )
  : mTriangularMesh( triangularMesh )
  , mNativeMesh( nativeMesh )
  , mDatasetValues( datasetValues )
  , mScalarActiveFaceFlagValues( scalarActiveFaceFlagValues )
{}
 
QgsMeshContours::~QgsMeshContours() = default;
 
QgsGeometry QgsMeshContours::exportPolygons( const QgsMeshDatasetIndex &index, double min_value, double max_value, QgsMeshRendererScalarSettings::DataResamplingMethod method, QgsFeedback *feedback )
{
  if ( !mMeshLayer )
    return QgsGeometry();
 
  populateCache( index, method );
 
  return exportPolygons( min_value, max_value, feedback );
}
 
QgsGeometry QgsMeshContours::exportPolygons( double min_value, double max_value, QgsFeedback *feedback )
{
  if ( min_value > max_value )
  {
    const double tmp = max_value;
    max_value = min_value;
    min_value = tmp;
  }
 
  QVector<QgsGeometry> multiPolygon;
 
  // STEP 1: Get Data
  const QVector<QgsMeshVertex> vertices = mTriangularMesh.vertices();
  const QVector<int> &trianglesToNativeFaces = mTriangularMesh.trianglesToNativeFaces();
 
  // STEP 2: For each triangle get the contour line
  for ( int i = 0; i < mTriangularMesh.triangles().size(); ++i )
  {
    if ( feedback && feedback->isCanceled() )
      break;
 
    const int nativeIndex = trianglesToNativeFaces.at( i );
    if ( !mScalarActiveFaceFlagValues.active( nativeIndex ) )
      continue;
 
    const QgsMeshFace &triangle = mTriangularMesh.triangles().at( i );
    const int indices[3] = { triangle.at( 0 ), triangle.at( 1 ), triangle.at( 2 ) };
 
    const QVector<QgsMeshVertex> coords = { vertices.at( indices[0] ), vertices.at( indices[1] ), vertices.at( indices[2] ) };
 
    const double values[3] = { mDatasetValues.at( indices[0] ), mDatasetValues.at( indices[1] ), mDatasetValues.at( indices[2] ) };
 
    // any value is NaN
    if ( std::isnan( values[0] ) || std::isnan( values[1] ) || std::isnan( values[2] ) )
      continue;
 
    // all values on vertices are outside the range
    if ( ( ( min_value > values[0] ) && ( min_value > values[1] ) && ( min_value > values[2] ) ) || ( ( max_value < values[0] ) && ( max_value < values[1] ) && ( max_value < values[2] ) ) )
      continue;
 
    const bool valueInRange[3]
      = { ( min_value <= values[0] ) && ( max_value >= values[0] ), ( min_value <= values[1] ) && ( max_value >= values[1] ), ( min_value <= values[2] ) && ( max_value >= values[2] ) };
 
    // all values are inside the range == take whole triangle
    if ( valueInRange[0] && valueInRange[1] && valueInRange[2] )
    {
      QVector<QgsMeshVertex> ring = coords;
      ring.push_back( coords[0] );
      auto ext = std::make_unique<QgsLineString>( coords );
      auto poly = std::make_unique<QgsPolygon>();
      poly->setExteriorRing( ext.release() );
      multiPolygon.push_back( QgsGeometry( std::move( poly ) ) );
      continue;
    }
 
    // go through all edges
    QVector<QgsMeshVertex> ring;
    for ( int i = 0; i < 3; ++i )
    {
      const int j = ( i + 1 ) % 3;
 
      if ( valueInRange[i] )
      {
        if ( valueInRange[j] )
        {
          // whole edge is part of resulting contour polygon edge
          if ( !ring.contains( coords[i] ) )
            ring.push_back( coords[i] );
          if ( !ring.contains( coords[j] ) )
            ring.push_back( coords[j] );
        }
        else
        {
          // i is part or the resulting edge
          if ( !ring.contains( coords[i] ) )
            ring.push_back( coords[i] );
          // we need to find the other point
          double value = max_value;
          if ( values[i] > values[j] )
          {
            value = min_value;
          }
          const double fraction = ( value - values[i] ) / ( values[j] - values[i] );
          const QgsPoint xy = QgsGeometryUtils::interpolatePointOnLine( coords[i], coords[j], fraction );
          if ( !ring.contains( xy ) )
            ring.push_back( xy );
        }
      }
      else
      {
        if ( valueInRange[j] )
        {
          // we need to find the other point
          double value = max_value;
          if ( values[i] < values[j] )
          {
            value = min_value;
          }
 
          const double fraction = ( value - values[i] ) / ( values[j] - values[i] );
          const QgsPoint xy = QgsGeometryUtils::interpolatePointOnLine( coords[i], coords[j], fraction );
          if ( !ring.contains( xy ) )
            ring.push_back( xy );
 
          // j is part
          if ( !ring.contains( coords[j] ) )
            ring.push_back( coords[j] );
        }
        else
        {
          // last option we need to consider is that both min and max are between
          // value i and j, and in that case we need to calculate both point
          double value1 = max_value;
          double value2 = max_value;
          if ( values[i] < values[j] )
          {
            if ( ( min_value < values[i] ) || ( max_value > values[j] ) )
            {
              continue;
            }
            value1 = min_value;
          }
          else
          {
            if ( ( min_value < values[j] ) || ( max_value > values[i] ) )
            {
              continue;
            }
            value2 = min_value;
          }
 
          const double fraction1 = ( value1 - values[i] ) / ( values[j] - values[i] );
          const QgsPoint xy1 = QgsGeometryUtils::interpolatePointOnLine( coords[i], coords[j], fraction1 );
          if ( !ring.contains( xy1 ) )
            ring.push_back( xy1 );
 
          const double fraction2 = ( value2 - values[i] ) / ( values[j] - values[i] );
          const QgsPoint xy2 = QgsGeometryUtils::interpolatePointOnLine( coords[i], coords[j], fraction2 );
          if ( !ring.contains( xy2 ) )
            ring.push_back( xy2 );
        }
      }
    }
 
    // add if the polygon is not degraded
    if ( ring.size() > 2 )
    {
      auto ext = std::make_unique<QgsLineString>( ring );
      auto poly = std::make_unique<QgsPolygon>();
      poly->setExteriorRing( ext.release() );
      multiPolygon.push_back( QgsGeometry( std::move( poly ) ) );
    }
  }
 
  // STEP 3: dissolve the individual polygons from triangles if possible
  if ( multiPolygon.isEmpty() )
  {
    return QgsGeometry();
  }
  else
  {
    const QgsGeometry res = QgsGeometry::unaryUnion( multiPolygon, QgsGeometryParameters(), feedback );
    return res;
  }
}
 
QgsGeometry QgsMeshContours::exportLines( const QgsMeshDatasetIndex &index, double value, QgsMeshRendererScalarSettings::DataResamplingMethod method, QgsFeedback *feedback )
{
  // Check if the layer/mesh is valid
  if ( !mMeshLayer )
    return QgsGeometry();
 
  populateCache( index, method );
 
  return exportLines( value, feedback );
}
 
QgsGeometry QgsMeshContours::exportLines( double value, QgsFeedback *feedback )
{
  auto multiLineString = std::make_unique<QgsMultiLineString>();
  QSet<QPair<int, int>> exactEdges;
 
  // STEP 1: Get Data
  const QVector<QgsMeshVertex> vertices = mTriangularMesh.vertices();
  const QVector<int> &trianglesToNativeFaces = mTriangularMesh.trianglesToNativeFaces();
 
  // STEP 2: For each triangle get the contour line
  for ( int i = 0; i < mTriangularMesh.triangles().size(); ++i )
  {
    if ( feedback && feedback->isCanceled() )
      break;
 
    const int nativeIndex = trianglesToNativeFaces.at( i );
    if ( !mScalarActiveFaceFlagValues.active( nativeIndex ) )
      continue;
 
    const QgsMeshFace &triangle = mTriangularMesh.triangles().at( i );
 
    const int indices[3] = { triangle.at( 0 ), triangle.at( 1 ), triangle.at( 2 ) };
 
    const QVector<QgsMeshVertex> coords = { vertices.at( indices[0] ), vertices.at( indices[1] ), vertices.at( indices[2] ) };
 
    const double values[3] = { mDatasetValues.at( indices[0] ), mDatasetValues.at( indices[1] ), mDatasetValues.at( indices[2] ) };
 
    // any value is NaN
    if ( std::isnan( values[0] ) || std::isnan( values[1] ) || std::isnan( values[2] ) )
      continue;
 
    // value is outside the range
    if ( ( ( value > values[0] ) && ( value > values[1] ) && ( value > values[2] ) ) || ( ( value < values[0] ) && ( value < values[1] ) && ( value < values[2] ) ) )
      continue;
 
    // all values are the same
    if ( qgsDoubleNear( values[0], values[1] ) && qgsDoubleNear( values[1], values[2] ) )
      continue;
 
    // go through all edges
    QgsPoint tmp;
 
    for ( int i = 0; i < 3; ++i )
    {
      const int j = ( i + 1 ) % 3;
      // value is outside the range
      if ( ( ( value > values[i] ) && ( value > values[j] ) ) || ( ( value < values[i] ) && ( value < values[j] ) ) )
        continue;
 
      // the whole edge is result and we are done
      if ( qgsDoubleNear( values[i], values[j] ) && qgsDoubleNear( values[i], values[j] ) )
      {
        if ( exactEdges.contains( { indices[i], indices[j] } ) || exactEdges.contains( { indices[j], indices[i] } ) )
        {
          break;
        }
        else
        {
          exactEdges.insert( { indices[i], indices[j] } );
          auto line = std::make_unique<QgsLineString>( coords[i], coords[j] );
          multiLineString->addGeometry( line.release() );
          break;
        }
      }
 
      // only one point matches, we are not interested in this
      if ( qgsDoubleNear( values[i], value ) || qgsDoubleNear( values[j], value ) )
      {
        continue;
      }
 
      // ok part of the result contour line is one point on this edge
      const double fraction = ( value - values[i] ) / ( values[j] - values[i] );
      const QgsPoint xy = QgsGeometryUtils::interpolatePointOnLine( coords[i], coords[j], fraction );
 
      if ( std::isnan( tmp.x() ) )
      {
        // ok we have found start point of the contour line
        tmp = xy;
      }
      else
      {
        // we have found the end point of the contour line, we are done
        auto line = std::make_unique<QgsLineString>( tmp, xy );
        multiLineString->addGeometry( line.release() );
        break;
      }
    }
  }
 
  // STEP 3: merge the contour segments to linestrings
  if ( multiLineString->isEmpty() )
  {
    return QgsGeometry();
  }
  else
  {
    const QgsGeometry in( multiLineString.release() );
    const QgsGeometry res = in.mergeLines();
    return res;
  }
}
 
void QgsMeshContours::populateCache( const QgsMeshDatasetIndex &index, QgsMeshRendererScalarSettings::DataResamplingMethod method )
{
  if ( !mMeshLayer )
    return;
 
  if ( mCachedIndex != index )
  {
    const bool scalarDataOnVertices = mMeshLayer->dataProvider()->datasetGroupMetadata( index ).dataType() == QgsMeshDatasetGroupMetadata::DataOnVertices;
    const int count = scalarDataOnVertices ? mNativeMesh.vertices.count() : mNativeMesh.faces.count();
 
    // populate scalar values
    const QgsMeshDataBlock vals = QgsMeshLayerUtils::datasetValues( mMeshLayer, index, 0, count );
    if ( vals.isValid() )
    {
      // vals could be scalar or vectors, for contour rendering we want always magnitude
      mDatasetValues = QgsMeshLayerUtils::calculateMagnitudes( vals );
    }
    else
    {
      mDatasetValues = QVector<double>( count, std::numeric_limits<double>::quiet_NaN() );
    }
 
    // populate face active flag, always defined on faces
    mScalarActiveFaceFlagValues = mMeshLayer->dataProvider()->areFacesActive( index, 0, mNativeMesh.faces.count() );
 
    // for data on faces, there could be request to interpolate the data to vertices
    if ( ( !scalarDataOnVertices ) )
    {
      mDatasetValues = QgsMeshLayerUtils::interpolateFromFacesData( mDatasetValues, &mNativeMesh, &mTriangularMesh, &mScalarActiveFaceFlagValues, method );
    }
  }
}