qgscircularstring.cpp

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/***************************************************************************
                         qgscircularstring.cpp
                         -----------------------
    begin                : September 2014
    copyright            : (C) 2014 by Marco Hugentobler
    email                : marco at sourcepole dot ch
 ***************************************************************************/
 
/***************************************************************************
 *                                                                         *
 *   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 "qgscircularstring.h"
 
#include <memory>
#include <nlohmann/json.hpp>
 
#include "qgsbox3d.h"
#include "qgscoordinatetransform.h"
#include "qgsgeometryutils.h"
#include "qgsgeometryutils_base.h"
#include "qgslinestring.h"
#include "qgspoint.h"
#include "qgspolygon.h"
#include "qgsrectangle.h"
 
#include <QJsonObject>
#include <QPainter>
#include <QPainterPath>
#include <QString>
 
using namespace Qt::StringLiterals;
 
QgsCircularString::QgsCircularString()
{
  mWkbType = Qgis::WkbType::CircularString;
}
 
QgsCircularString::QgsCircularString( const QgsPoint &p1, const QgsPoint &p2, const QgsPoint &p3 )
{
  //get wkb type from first point
  bool hasZ = p1.is3D();
  bool hasM = p1.isMeasure();
  mWkbType = Qgis::WkbType::CircularString;
 
  mX.resize( 3 );
  mX[0] = p1.x();
  mX[1] = p2.x();
  mX[2] = p3.x();
  mY.resize( 3 );
  mY[0] = p1.y();
  mY[1] = p2.y();
  mY[2] = p3.y();
  if ( hasZ )
  {
    mWkbType = QgsWkbTypes::addZ( mWkbType );
    mZ.resize( 3 );
    mZ[0] = p1.z();
    mZ[1] = p2.z();
    mZ[2] = p3.z();
  }
  if ( hasM )
  {
    mWkbType = QgsWkbTypes::addM( mWkbType );
    mM.resize( 3 );
    mM[0] = p1.m();
    mM[1] = p2.m();
    mM[2] = p3.m();
  }
}
 
QgsCircularString::QgsCircularString( const QVector<double> &x, const QVector<double> &y, const QVector<double> &z, const QVector<double> &m )
{
  mWkbType = Qgis::WkbType::CircularString;
  int pointCount = std::min( x.size(), y.size() );
  if ( x.size() == pointCount )
  {
    mX = x;
  }
  else
  {
    mX = x.mid( 0, pointCount );
  }
  if ( y.size() == pointCount )
  {
    mY = y;
  }
  else
  {
    mY = y.mid( 0, pointCount );
  }
  if ( !z.isEmpty() && z.count() >= pointCount )
  {
    mWkbType = Qgis::WkbType::CircularStringZ;
    if ( z.size() == pointCount )
    {
      mZ = z;
    }
    else
    {
      mZ = z.mid( 0, pointCount );
    }
  }
  if ( !m.isEmpty() && m.count() >= pointCount )
  {
    mWkbType = QgsWkbTypes::addM( mWkbType );
    if ( m.size() == pointCount )
    {
      mM = m;
    }
    else
    {
      mM = m.mid( 0, pointCount );
    }
  }
}
 
QgsCircularString QgsCircularString::fromTwoPointsAndCenter( const QgsPoint &p1, const QgsPoint &p2, const QgsPoint &center, const bool useShortestArc )
{
  const QgsPoint midPoint = QgsGeometryUtils::segmentMidPointFromCenter( p1, p2, center, useShortestArc );
  return QgsCircularString( p1, midPoint, p2 );
}
 
QgsCircularString *QgsCircularString::createEmptyWithSameType() const
{
  auto result = std::make_unique< QgsCircularString >();
  result->mWkbType = mWkbType;
  return result.release();
}
 
QString QgsCircularString::geometryType() const
{
  return u"CircularString"_s;
}
 
QgsCircularString *QgsCircularString::clone() const
{
  return new QgsCircularString( *this );
}
 
void QgsCircularString::clear()
{
  mWkbType = Qgis::WkbType::CircularString;
  QgsSimpleCurve::clear();
}
 
QgsBox3D QgsCircularString::calculateBoundingBox3D() const
{
  QgsBox3D bbox;
  int nPoints = numPoints();
  for ( int i = 0; i < ( nPoints - 2 ); i += 2 )
  {
    QgsRectangle box2d = segmentBoundingBox( QgsPoint( mX[i], mY[i] ), QgsPoint( mX[i + 1], mY[i + 1] ), QgsPoint( mX[i + 2], mY[i + 2] ) );
    double zMin = std::numeric_limits<double>::quiet_NaN();
    double zMax = std::numeric_limits<double>::quiet_NaN();
    if ( is3D() )
    {
      zMin = *std::min_element( mZ.begin() + i, mZ.begin() + i + 3 );
      zMax = *std::max_element( mZ.begin() + i, mZ.begin() + i + 3 );
    }
    if ( i == 0 )
    {
      bbox = QgsBox3D( box2d, zMin, zMax );
    }
    else
    {
      bbox.combineWith( QgsBox3D( box2d, zMin, zMax ) );
    }
  }
 
  if ( nPoints > 0 && nPoints % 2 == 0 )
  {
    double z = std::numeric_limits<double>::quiet_NaN();
    if ( nPoints == 2 )
    {
      if ( is3D() )
      {
        z = mZ[0];
      }
      bbox.combineWith( mX[0], mY[0], z );
    }
    if ( is3D() )
    {
      z = mZ[nPoints - 1];
    }
    bbox.combineWith( mX[nPoints - 1], mY[nPoints - 1], z );
  }
  return bbox;
}
 
QgsRectangle QgsCircularString::segmentBoundingBox( const QgsPoint &pt1, const QgsPoint &pt2, const QgsPoint &pt3 )
{
  double centerX, centerY, radius;
  QgsGeometryUtils::circleCenterRadius( pt1, pt2, pt3, radius, centerX, centerY );
 
  double p1Angle = QgsGeometryUtilsBase::ccwAngle( pt1.y() - centerY, pt1.x() - centerX );
  double p2Angle = QgsGeometryUtilsBase::ccwAngle( pt2.y() - centerY, pt2.x() - centerX );
  double p3Angle = QgsGeometryUtilsBase::ccwAngle( pt3.y() - centerY, pt3.x() - centerX );
 
  //start point, end point and compass points in between can be on bounding box
  QgsRectangle bbox( pt1.x(), pt1.y(), pt1.x(), pt1.y() );
  bbox.combineExtentWith( pt3.x(), pt3.y() );
 
  QgsPointSequence compassPoints = compassPointsOnSegment( p1Angle, p2Angle, p3Angle, centerX, centerY, radius );
  QgsPointSequence::const_iterator cpIt = compassPoints.constBegin();
  for ( ; cpIt != compassPoints.constEnd(); ++cpIt )
  {
    bbox.combineExtentWith( cpIt->x(), cpIt->y() );
  }
  return bbox;
}
 
QgsPointSequence QgsCircularString::compassPointsOnSegment( double p1Angle, double p2Angle, double p3Angle, double centerX, double centerY, double radius )
{
  QgsPointSequence pointList;
 
  QgsPoint nPoint( centerX, centerY + radius );
  QgsPoint ePoint( centerX + radius, centerY );
  QgsPoint sPoint( centerX, centerY - radius );
  QgsPoint wPoint( centerX - radius, centerY );
 
  if ( p3Angle >= p1Angle )
  {
    if ( p2Angle > p1Angle && p2Angle < p3Angle )
    {
      if ( p1Angle <= 90 && p3Angle >= 90 )
      {
        pointList.append( nPoint );
      }
      if ( p1Angle <= 180 && p3Angle >= 180 )
      {
        pointList.append( wPoint );
      }
      if ( p1Angle <= 270 && p3Angle >= 270 )
      {
        pointList.append( sPoint );
      }
    }
    else
    {
      pointList.append( ePoint );
      if ( p1Angle >= 90 || p3Angle <= 90 )
      {
        pointList.append( nPoint );
      }
      if ( p1Angle >= 180 || p3Angle <= 180 )
      {
        pointList.append( wPoint );
      }
      if ( p1Angle >= 270 || p3Angle <= 270 )
      {
        pointList.append( sPoint );
      }
    }
  }
  else
  {
    if ( p2Angle < p1Angle && p2Angle > p3Angle )
    {
      if ( p1Angle >= 270 && p3Angle <= 270 )
      {
        pointList.append( sPoint );
      }
      if ( p1Angle >= 180 && p3Angle <= 180 )
      {
        pointList.append( wPoint );
      }
      if ( p1Angle >= 90 && p3Angle <= 90 )
      {
        pointList.append( nPoint );
      }
    }
    else
    {
      pointList.append( ePoint );
      if ( p1Angle <= 270 || p3Angle >= 270 )
      {
        pointList.append( sPoint );
      }
      if ( p1Angle <= 180 || p3Angle >= 180 )
      {
        pointList.append( wPoint );
      }
      if ( p1Angle <= 90 || p3Angle >= 90 )
      {
        pointList.append( nPoint );
      }
    }
  }
  return pointList;
}
 
QDomElement QgsCircularString::asGml2( QDomDocument &doc, int precision, const QString &ns, const AxisOrder axisOrder ) const
{
  // GML2 does not support curves
  std::unique_ptr< QgsLineString > line( curveToLine() );
  QDomElement gml = line->asGml2( doc, precision, ns, axisOrder );
  return gml;
}
 
QDomElement QgsCircularString::asGml3( QDomDocument &doc, int precision, const QString &ns, const QgsAbstractGeometry::AxisOrder axisOrder ) const
{
  QgsPointSequence pts;
  points( pts );
 
  QDomElement elemCurve = doc.createElementNS( ns, u"Curve"_s );
 
  if ( isEmpty() )
    return elemCurve;
 
  QDomElement elemSegments = doc.createElementNS( ns, u"segments"_s );
  QDomElement elemArcString = doc.createElementNS( ns, u"ArcString"_s );
  elemArcString.appendChild( QgsGeometryUtils::pointsToGML3( pts, doc, precision, ns, is3D(), axisOrder ) );
  elemSegments.appendChild( elemArcString );
  elemCurve.appendChild( elemSegments );
  return elemCurve;
}
 
 
json QgsCircularString::asJsonObject( int precision, Qgis::GeoJsonProfile profile ) const
{
  switch ( profile )
  {
    case Qgis::GeoJsonProfile::Legacy:
    case Qgis::GeoJsonProfile::Rfc7946:
    {
      std::unique_ptr< QgsLineString > line( curveToLine() );
      return line->asJsonObject( precision, profile );
    }
    case Qgis::GeoJsonProfile::JsonFg:
    case Qgis::GeoJsonProfile::JsonFgPlus:
    {
      QgsPointSequence pts;
      points( pts );
      // Work around the 11 points limit
      constexpr int MAX_POINT = 11;
      if ( pts.size() > MAX_POINT )
      {
        json geometries = json::array();
        json subCs = { { "type", "CircularString" } };
        subCs["coordinates"] = json::array();
        for ( int i = 0; i < pts.size(); i++ )
        {
          const json pointCoords = pts[i].asJsonObject( precision, profile )["coordinates"];
          subCs["coordinates"].push_back( pointCoords );
          if ( subCs["coordinates"].size() == MAX_POINT )
          {
            geometries.push_back( subCs );
            // Clear array
            subCs["coordinates"] = json::array();
            subCs["coordinates"].push_back( pointCoords );
          }
        }
        // Last one (if any)
        if ( subCs["coordinates"].size() > 1 )
        {
          geometries.push_back( subCs );
        }
        return { { "type", "CompoundCurve" }, { "geometries", geometries } };
      }
      else
      {
        return { { "type", "CircularString" }, { "coordinates", QgsGeometryUtils::pointsToJson( pts, precision, profile ) } };
      }
    }
  }
  BUILTIN_UNREACHABLE
}
 
bool QgsCircularString::isValid( QString &error, Qgis::GeometryValidityFlags flags ) const
{
  if ( !isEmpty() && ( numPoints() < 3 ) )
  {
    error = QObject::tr( "CircularString has less than 3 points and is not empty." );
    return false;
  }
  return QgsCurve::isValid( error, flags );
}
 
//curve interface
double QgsCircularString::length() const
{
  int nPoints = numPoints();
  double length = 0;
  for ( int i = 0; i < ( nPoints - 2 ); i += 2 )
  {
    length += QgsGeometryUtilsBase::circleLength( mX[i], mY[i], mX[i + 1], mY[i + 1], mX[i + 2], mY[i + 2] );
  }
  return length;
}
 
QgsLineString *QgsCircularString::curveToLine( double tolerance, SegmentationToleranceType toleranceType ) const
{
  QgsLineString *line = new QgsLineString();
  QgsPointSequence points;
  int nPoints = numPoints();
 
  for ( int i = 0; i < ( nPoints - 2 ); i += 2 )
  {
    QgsGeometryUtils::segmentizeArc( pointN( i ), pointN( i + 1 ), pointN( i + 2 ), points, tolerance, toleranceType, is3D(), isMeasure() );
  }
 
  line->setPoints( points );
  return line;
}
 
QgsCircularString *QgsCircularString::snappedToGrid( double hSpacing, double vSpacing, double dSpacing, double mSpacing, bool ) const
{
  // prepare result
  std::unique_ptr<QgsCircularString> result { createEmptyWithSameType() };
 
  // remove redundant not supported for circular strings
  bool res = snapToGridPrivate( hSpacing, vSpacing, dSpacing, mSpacing, mX, mY, mZ, mM, result->mX, result->mY, result->mZ, result->mM, false );
  if ( res )
    return result.release();
  else
    return nullptr;
}
 
QgsAbstractGeometry *QgsCircularString::simplifyByDistance( double tolerance ) const
{
  std::unique_ptr< QgsLineString > line( curveToLine() );
  return line->simplifyByDistance( tolerance );
}
 
bool QgsCircularString::removeDuplicateNodes( double epsilon, bool useZValues )
{
  if ( mX.count() <= 3 )
    return false; // don't create degenerate lines
  bool result = false;
  double prevX = mX.at( 0 );
  double prevY = mY.at( 0 );
  bool hasZ = is3D();
  bool useZ = hasZ && useZValues;
  double prevZ = useZ ? mZ.at( 0 ) : 0;
  int i = 1;
  int remaining = mX.count();
  // we have to consider points in pairs, since a segment can validly have the same start and
  // end if it has a different curve point
  while ( i + 1 < remaining )
  {
    double currentCurveX = mX.at( i );
    double currentCurveY = mY.at( i );
    double currentX = mX.at( i + 1 );
    double currentY = mY.at( i + 1 );
    double currentZ = useZ ? mZ.at( i + 1 ) : 0;
    if ( qgsDoubleNear( currentCurveX, prevX, epsilon )
         && qgsDoubleNear( currentCurveY, prevY, epsilon )
         && qgsDoubleNear( currentX, prevX, epsilon )
         && qgsDoubleNear( currentY, prevY, epsilon )
         && ( !useZ || qgsDoubleNear( currentZ, prevZ, epsilon ) ) )
    {
      result = true;
      // remove point
      mX.removeAt( i );
      mX.removeAt( i );
      mY.removeAt( i );
      mY.removeAt( i );
      if ( hasZ )
      {
        mZ.removeAt( i );
        mZ.removeAt( i );
      }
      remaining -= 2;
    }
    else
    {
      prevX = currentX;
      prevY = currentY;
      prevZ = currentZ;
      i += 2;
    }
  }
  return result;
}
 
int QgsCircularString::indexOf( const QgsPoint &point ) const
{
  const int size = mX.size();
  if ( size == 0 )
    return -1;
 
  const double *x = mX.constData();
  const double *y = mY.constData();
  const bool useZ = is3D();
  const bool useM = isMeasure();
  const double *z = useZ ? mZ.constData() : nullptr;
  const double *m = useM ? mM.constData() : nullptr;
 
  for ( int i = 0; i < size; i += 2 )
  {
    if ( qgsDoubleNear( *x, point.x() ) && qgsDoubleNear( *y, point.y() ) && ( !useZ || qgsDoubleNear( *z, point.z() ) ) && ( !useM || qgsDoubleNear( *m, point.m() ) ) )
      return i;
 
    // we skip over curve points!
    x++;
    x++;
    y++;
    y++;
    if ( useZ )
    {
      z++;
      z++;
    }
    if ( useM )
    {
      m++;
      m++;
    }
  }
  return -1;
}
 
std::tuple<std::unique_ptr<QgsCurve>, std::unique_ptr<QgsCurve> > QgsCircularString::splitCurveAtVertex( int index ) const
{
  QVector< double > x1, y1, z1, m1;
  QVector< double > x2, y2, z2, m2;
  QgsSimpleCurve::splitCurveAtVertexProtected( index, x1, y1, z1, m1, x2, y2, z2, m2 );
 
  std::unique_ptr< QgsCircularString > first;
  if ( x1.isEmpty() || ( x1.size() < 2 && x2.size() >= 2 ) )
    first = std::make_unique< QgsCircularString >();
  else
    first = std::make_unique< QgsCircularString >( x1, y1, z1, m1 );
 
  std::unique_ptr< QgsCircularString > second;
  if ( x2.isEmpty() || x2.size() < 2 )
    second = std::make_unique< QgsCircularString >();
  else
    second = std::make_unique< QgsCircularString >( x2, y2, z2, m2 );
 
  return std::make_tuple( std::move( first ), std::move( second ) );
}
 
void QgsCircularString::draw( QPainter &p ) const
{
  QPainterPath path;
  addToPainterPath( path );
  p.drawPath( path );
}
 
void arcTo( QPainterPath &path, QPointF pt1, QPointF pt2, QPointF pt3 )
{
  double centerX, centerY, radius;
  QgsGeometryUtils::circleCenterRadius( QgsPoint( pt1.x(), pt1.y() ), QgsPoint( pt2.x(), pt2.y() ), QgsPoint( pt3.x(), pt3.y() ), radius, centerX, centerY );
 
  double p1Angle = QgsGeometryUtilsBase::ccwAngle( pt1.y() - centerY, pt1.x() - centerX );
  double sweepAngle = QgsGeometryUtilsBase::sweepAngle( centerX, centerY, pt1.x(), pt1.y(), pt2.x(), pt2.y(), pt3.x(), pt3.y() );
 
  double diameter = 2 * radius;
  path.arcTo( centerX - radius, centerY - radius, diameter, diameter, -p1Angle, -sweepAngle );
}
 
void QgsCircularString::addToPainterPath( QPainterPath &path ) const
{
  int nPoints = numPoints();
  if ( nPoints < 1 )
  {
    return;
  }
 
  if ( path.isEmpty() || path.currentPosition() != QPointF( mX[0], mY[0] ) )
  {
    path.moveTo( QPointF( mX[0], mY[0] ) );
  }
 
  for ( int i = 0; i < ( nPoints - 2 ); i += 2 )
  {
    arcTo( path, QPointF( mX[i], mY[i] ), QPointF( mX[i + 1], mY[i + 1] ), QPointF( mX[i + 2], mY[i + 2] ) );
  }
 
  //if number of points is even, connect to last point with straight line (even though the circular string is not valid)
  if ( nPoints % 2 == 0 )
  {
    path.lineTo( mX[nPoints - 1], mY[nPoints - 1] );
  }
}
 
void QgsCircularString::drawAsPolygon( QPainter &p ) const
{
  draw( p );
}
 
bool QgsCircularString::insertVertex( QgsVertexId position, const QgsPoint &vertex )
{
  if ( position.vertex >= mX.size() || position.vertex < 1 )
  {
    return false;
  }
 
  mX.insert( position.vertex, vertex.x() );
  mY.insert( position.vertex, vertex.y() );
  if ( is3D() )
  {
    mZ.insert( position.vertex, vertex.z() );
  }
  if ( isMeasure() )
  {
    mM.insert( position.vertex, vertex.m() );
  }
 
  bool vertexNrEven = ( position.vertex % 2 == 0 );
  if ( vertexNrEven )
  {
    insertVertexBetween( position.vertex - 2, position.vertex - 1, position.vertex );
  }
  else
  {
    insertVertexBetween( position.vertex, position.vertex + 1, position.vertex - 1 );
  }
  clearCache(); //set bounding box invalid
  return true;
}
 
void QgsCircularString::removeVertexAt( int i )
{
  mX.remove( i );
  mY.remove( i );
  if ( is3D() )
  {
    mZ.remove( i );
  }
  if ( isMeasure() )
  {
    mM.remove( i );
  }
  clearCache();
}
 
bool QgsCircularString::deleteVertices( const QSet<QgsVertexId> &positions )
{
  if ( positions.empty() )
  {
    return false;
  }
 
  for ( QgsVertexId pos : positions )
  {
    if ( !hasVertex( pos ) )
    {
      return false;
    }
  }
 
  int nVertices = this->numPoints();
 
  QList<QgsVertexId> vertices( positions.begin(), positions.end() );
 
  std::sort( vertices.begin(), vertices.end(), []( const QgsVertexId &a, const QgsVertexId &b ) { return a.vertex < b.vertex; } );
 
  // remove adjacent vertices as deleting one will also delete the other
  for ( size_t i = vertices.size() - 1; i >= 1; i-- )
  {
    int vertexNr = vertices[i].vertex;
    int prevVertexNr = vertices[i - 1].vertex;
 
    if ( vertexNr - 1 == prevVertexNr )
    {
      if ( vertexNr < nVertices - 2 )
      {
        vertices.removeAt( i );
      }
      else
      {
        vertices.removeAt( i - 1 );
      }
 
      i--; // adjacent vertices handled, we can skip the next one as well
 
      if ( i == 0 )
        break;
    }
  }
 
  // this check cannot be moved further up, we need to check adjacent vertices first
  if ( nVertices - vertices.size() * 2 < 3 )
  {
    clear();
    return true;
  }
 
  QListIterator<QgsVertexId> positionsIt( vertices );
  positionsIt.toBack();
  while ( positionsIt.hasPrevious() )
  {
    int currentVertexNr = positionsIt.previous().vertex;
 
    if ( currentVertexNr < nVertices - 2 )
    {
      removeVertexAt( currentVertexNr + 1 );
      removeVertexAt( currentVertexNr );
    }
    else
    {
      removeVertexAt( currentVertexNr );
      removeVertexAt( currentVertexNr - 1 );
    }
    nVertices -= 2;
  }
 
  return true;
}
 
double QgsCircularString::closestSegment( const QgsPoint &pt, QgsPoint &segmentPt, QgsVertexId &vertexAfter, int *leftOf, double epsilon ) const
{
  double minDist = std::numeric_limits<double>::max();
  QgsPoint minDistSegmentPoint;
  QgsVertexId minDistVertexAfter;
  int minDistLeftOf = 0;
 
  double currentDist = 0.0;
 
  int nPoints = numPoints();
  for ( int i = 0; i < ( nPoints - 2 ); i += 2 )
  {
    currentDist = closestPointOnArc( mX[i], mY[i], mX[i + 1], mY[i + 1], mX[i + 2], mY[i + 2], pt, segmentPt, vertexAfter, leftOf, epsilon );
    if ( currentDist < minDist )
    {
      minDist = currentDist;
      minDistSegmentPoint = segmentPt;
      minDistVertexAfter.vertex = vertexAfter.vertex + i;
      if ( leftOf )
      {
        minDistLeftOf = *leftOf;
      }
    }
  }
 
  if ( minDist == std::numeric_limits<double>::max() )
    return -1; // error: no segments
 
  segmentPt = minDistSegmentPoint;
  vertexAfter = minDistVertexAfter;
  vertexAfter.part = 0;
  vertexAfter.ring = 0;
  if ( leftOf )
  {
    *leftOf = qgsDoubleNear( minDist, 0.0 ) ? 0 : minDistLeftOf;
  }
  return minDist;
}
 
bool QgsCircularString::pointAt( int node, QgsPoint &point, Qgis::VertexType &type ) const
{
  if ( node < 0 || node >= numPoints() )
  {
    return false;
  }
  point = pointN( node );
  type = ( node % 2 == 0 ) ? Qgis::VertexType::Segment : Qgis::VertexType::Curve;
  return true;
}
 
void QgsCircularString::sumUpArea( double &sum ) const
{
  if ( mHasCachedSummedUpArea )
  {
    sum += mSummedUpArea;
    return;
  }
 
  int maxIndex = numPoints() - 2;
  mSummedUpArea = 0;
  for ( int i = 0; i < maxIndex; i += 2 )
  {
    QgsPoint p1( mX[i], mY[i] );
    QgsPoint p2( mX[i + 1], mY[i + 1] );
    QgsPoint p3( mX[i + 2], mY[i + 2] );
 
    //segment is a full circle, p2 is the center point
    if ( p1 == p3 )
    {
      double r2 = QgsGeometryUtils::sqrDistance2D( p1, p2 ) / 4.0;
      mSummedUpArea += M_PI * r2;
      continue;
    }
 
    mSummedUpArea += 0.5 * ( mX[i] * mY[i + 2] - mY[i] * mX[i + 2] );
 
    //calculate area between circle and chord, then sum / subtract from total area
    double midPointX = ( p1.x() + p3.x() ) / 2.0;
    double midPointY = ( p1.y() + p3.y() ) / 2.0;
 
    double radius, centerX, centerY;
    QgsGeometryUtils::circleCenterRadius( p1, p2, p3, radius, centerX, centerY );
 
    double d = std::sqrt( QgsGeometryUtils::sqrDistance2D( QgsPoint( centerX, centerY ), QgsPoint( midPointX, midPointY ) ) );
    double r2 = radius * radius;
 
    if ( d > radius )
    {
      //d cannot be greater than radius, something must be wrong...
      continue;
    }
 
    bool circlePointLeftOfLine = QgsGeometryUtilsBase::leftOfLine( p2.x(), p2.y(), p1.x(), p1.y(), p3.x(), p3.y() ) < 0;
    bool centerPointLeftOfLine = QgsGeometryUtilsBase::leftOfLine( centerX, centerY, p1.x(), p1.y(), p3.x(), p3.y() ) < 0;
 
    double cov = 0.5 - d * std::sqrt( r2 - d * d ) / ( M_PI * r2 ) - M_1_PI * std::asin( d / radius );
    double circleChordArea = 0;
    if ( circlePointLeftOfLine == centerPointLeftOfLine )
    {
      circleChordArea = M_PI * r2 * ( 1 - cov );
    }
    else
    {
      circleChordArea = M_PI * r2 * cov;
    }
 
    if ( !circlePointLeftOfLine )
    {
      mSummedUpArea += circleChordArea;
    }
    else
    {
      mSummedUpArea -= circleChordArea;
    }
  }
 
  mHasCachedSummedUpArea = true;
  sum += mSummedUpArea;
}
 
void QgsCircularString::sumUpArea3D( double &sum ) const
{
  if ( mHasCachedSummedUpArea3D )
  {
    sum += mSummedUpArea3D;
    return;
  }
 
  // No Z component. Fallback to the 2D version
  if ( mZ.isEmpty() )
  {
    double area2D = 0;
    sumUpArea( area2D );
    mSummedUpArea3D = area2D;
    mHasCachedSummedUpArea3D = true;
    sum += mSummedUpArea3D;
    return;
  }
 
  // FIXME: Implement proper 3D shoelace formula for circular strings
  // workaround: project points to 2D plane and apply standard 2D shoelace formula
  mSummedUpArea3D = 0;
 
  // Build an orthonormal reference frame (ux, uy, uz) from three 3D points
  QgsPoint ptA;
  QgsPoint ptB;
  QgsPoint ptC;
  if ( !QgsGeometryUtils::checkWeaklyFor3DPlane( this, ptA, ptB, ptC ) )
  {
    mHasCachedSummedUpArea3D = true;
    return;
  }
 
  QgsVector3D ux( ptB.x() - ptA.x(), ptB.y() - ptA.y(), ptB.z() - ptA.z() );
  QgsVector3D uz = QgsVector3D::crossProduct( ux, QgsVector3D( ptC.x() - ptA.x(), ptC.y() - ptA.y(), ptC.z() - ptA.z() ) );
  ux.normalize();
  uz.normalize();
  QgsVector3D uy = QgsVector3D::crossProduct( uz, ux );
 
  double normalSign = 1.0;
  // Ensure a consistent orientation: prioritize Z+, then Y+, then X+
  if ( !qgsDoubleNear( uz.z(), 0.0 ) )
  {
    if ( uz.z() < 0 )
      normalSign = -1.0;
  }
  else if ( !qgsDoubleNear( uz.y(), 0.0 ) )
  {
    if ( uz.y() < 0 )
      normalSign = -1.0;
  }
  else
  {
    if ( uz.x() < 0 )
      normalSign = -1.0;
  }
 
  // Project points onto the orthonormal plane (ux, uy) and compute 2D sumUpArea
  const int nrPoints = numPoints();
  QVector<double> projX;
  QVector<double> projY;
  projX.reserve( nrPoints );
  projY.reserve( nrPoints );
  for ( int i = 0; i < nrPoints; i++ )
  {
    const double vecAX = mX[i] - ptA.x();
    const double vecAY = mY[i] - ptA.y();
    const double vecAZ = mZ[i] - ptA.z();
 
    projX.push_back( vecAX * ux.x() + vecAY * ux.y() + vecAZ * ux.z() );
    projY.push_back( vecAX * uy.x() + vecAY * uy.y() + vecAZ * uy.z() );
  }
 
  QgsCircularString projectedCurve( projX, projY );
  projectedCurve.sumUpArea( mSummedUpArea3D );
 
  // take into account normal sign
  mSummedUpArea3D *= normalSign;
  mHasCachedSummedUpArea3D = true;
  sum += mSummedUpArea3D;
}
 
bool QgsCircularString::hasCurvedSegments() const
{
  return true;
}
 
double QgsCircularString::closestPointOnArc( double x1, double y1, double x2, double y2, double x3, double y3, const QgsPoint &pt, QgsPoint &segmentPt, QgsVertexId &vertexAfter, int *leftOf, double epsilon )
{
  double radius, centerX, centerY;
  QgsPoint pt1( x1, y1 );
  QgsPoint pt2( x2, y2 );
  QgsPoint pt3( x3, y3 );
 
  QgsGeometryUtils::circleCenterRadius( pt1, pt2, pt3, radius, centerX, centerY );
  double angle = QgsGeometryUtilsBase::ccwAngle( pt.y() - centerY, pt.x() - centerX );
  double angle1 = QgsGeometryUtilsBase::ccwAngle( pt1.y() - centerY, pt1.x() - centerX );
  double angle2 = QgsGeometryUtilsBase::ccwAngle( pt2.y() - centerY, pt2.x() - centerX );
  double angle3 = QgsGeometryUtilsBase::ccwAngle( pt3.y() - centerY, pt3.x() - centerX );
 
  bool clockwise = QgsGeometryUtilsBase::circleClockwise( angle1, angle2, angle3 );
 
  if ( QgsGeometryUtilsBase::angleOnCircle( angle, angle1, angle2, angle3 ) )
  {
    //get point on line center -> pt with distance radius
    segmentPt = QgsGeometryUtils::pointOnLineWithDistance( QgsPoint( centerX, centerY ), pt, radius );
 
    //vertexAfter
    vertexAfter.vertex = QgsGeometryUtilsBase::circleAngleBetween( angle, angle1, angle2, clockwise ) ? 1 : 2;
  }
  else
  {
    double distPtPt1 = QgsGeometryUtils::sqrDistance2D( pt, pt1 );
    double distPtPt3 = QgsGeometryUtils::sqrDistance2D( pt, pt3 );
    segmentPt = ( distPtPt1 <= distPtPt3 ) ? pt1 : pt3;
    vertexAfter.vertex = ( distPtPt1 <= distPtPt3 ) ? 1 : 2;
  }
 
  double sqrDistance = QgsGeometryUtils::sqrDistance2D( segmentPt, pt );
  //prevent rounding errors if the point is directly on the segment
  if ( qgsDoubleNear( sqrDistance, 0.0, epsilon ) )
  {
    segmentPt.setX( pt.x() );
    segmentPt.setY( pt.y() );
    sqrDistance = 0.0;
  }
 
  if ( leftOf )
  {
    double sqrDistancePointToCenter = pt.distanceSquared( centerX, centerY );
    *leftOf = clockwise ? ( sqrDistancePointToCenter > radius * radius ? -1 : 1 ) : ( sqrDistancePointToCenter < radius * radius ? -1 : 1 );
  }
 
  return sqrDistance;
}
 
void QgsCircularString::insertVertexBetween( int after, int before, int pointOnCircle )
{
  double xAfter = mX.at( after );
  double yAfter = mY.at( after );
  double xBefore = mX.at( before );
  double yBefore = mY.at( before );
  double xOnCircle = mX.at( pointOnCircle );
  double yOnCircle = mY.at( pointOnCircle );
 
  double radius, centerX, centerY;
  QgsGeometryUtils::circleCenterRadius( QgsPoint( xAfter, yAfter ), QgsPoint( xBefore, yBefore ), QgsPoint( xOnCircle, yOnCircle ), radius, centerX, centerY );
 
  double x = ( xAfter + xBefore ) / 2.0;
  double y = ( yAfter + yBefore ) / 2.0;
 
  QgsPoint newVertex = QgsGeometryUtils::pointOnLineWithDistance( QgsPoint( centerX, centerY ), QgsPoint( x, y ), radius );
  mX.insert( before, newVertex.x() );
  mY.insert( before, newVertex.y() );
 
  if ( is3D() )
  {
    mZ.insert( before, ( mZ[after] + mZ[before] ) / 2.0 );
  }
  if ( isMeasure() )
  {
    mM.insert( before, ( mM[after] + mM[before] ) / 2.0 );
  }
  clearCache();
}
 
double QgsCircularString::vertexAngle( QgsVertexId vId ) const
{
  if ( numPoints() < 3 )
  {
    //undefined
    return 0.0;
  }
 
  int before = vId.vertex - 1;
  int vertex = vId.vertex;
  int after = vId.vertex + 1;
 
  if ( vId.vertex % 2 != 0 ) // a curve vertex
  {
    if ( vId.vertex >= 1 && vId.vertex < numPoints() - 1 )
    {
      return QgsGeometryUtils::circleTangentDirection( QgsPoint( mX[vertex], mY[vertex] ), QgsPoint( mX[before], mY[before] ), QgsPoint( mX[vertex], mY[vertex] ), QgsPoint( mX[after], mY[after] ) );
    }
  }
  else //a point vertex
  {
    if ( vId.vertex == 0 )
    {
      return QgsGeometryUtils::circleTangentDirection( QgsPoint( mX[0], mY[0] ), QgsPoint( mX[0], mY[0] ), QgsPoint( mX[1], mY[1] ), QgsPoint( mX[2], mY[2] ) );
    }
    if ( vId.vertex >= numPoints() - 1 )
    {
      int a = numPoints() - 3;
      int b = numPoints() - 2;
      int c = numPoints() - 1;
      return QgsGeometryUtils::circleTangentDirection( QgsPoint( mX[c], mY[c] ), QgsPoint( mX[a], mY[a] ), QgsPoint( mX[b], mY[b] ), QgsPoint( mX[c], mY[c] ) );
    }
    else
    {
      if ( vId.vertex + 2 > numPoints() - 1 )
      {
        return 0.0;
      }
 
      int vertex1 = vId.vertex - 2;
      int vertex2 = vId.vertex - 1;
      int vertex3 = vId.vertex;
      double angle1
        = QgsGeometryUtils::circleTangentDirection( QgsPoint( mX[vertex3], mY[vertex3] ), QgsPoint( mX[vertex1], mY[vertex1] ), QgsPoint( mX[vertex2], mY[vertex2] ), QgsPoint( mX[vertex3], mY[vertex3] ) );
      int vertex4 = vId.vertex + 1;
      int vertex5 = vId.vertex + 2;
      double angle2
        = QgsGeometryUtils::circleTangentDirection( QgsPoint( mX[vertex3], mY[vertex3] ), QgsPoint( mX[vertex3], mY[vertex3] ), QgsPoint( mX[vertex4], mY[vertex4] ), QgsPoint( mX[vertex5], mY[vertex5] ) );
      return QgsGeometryUtilsBase::averageAngle( angle1, angle2 );
    }
  }
  return 0.0;
}
 
double QgsCircularString::segmentLength( QgsVertexId startVertex ) const
{
  if ( startVertex.vertex % 2 == 1 )
    return 0.0; // curve point?
 
  if ( startVertex.vertex < 0 || startVertex.vertex >= mX.count() - 2 )
    return 0.0;
 
  double x1 = mX.at( startVertex.vertex );
  double y1 = mY.at( startVertex.vertex );
  double x2 = mX.at( startVertex.vertex + 1 );
  double y2 = mY.at( startVertex.vertex + 1 );
  double x3 = mX.at( startVertex.vertex + 2 );
  double y3 = mY.at( startVertex.vertex + 2 );
  return QgsGeometryUtilsBase::circleLength( x1, y1, x2, y2, x3, y3 );
}
 
double QgsCircularString::distanceBetweenVertices( QgsVertexId fromVertex, QgsVertexId toVertex ) const
{
  // Ensure fromVertex < toVertex for simplicity
  if ( fromVertex.vertex > toVertex.vertex )
  {
    return distanceBetweenVertices( toVertex, fromVertex );
  }
 
  // Convert QgsVertexId to simple vertex numbers for curves (single ring, single part)
  if ( fromVertex.part != 0 || fromVertex.ring != 0 || toVertex.part != 0 || toVertex.ring != 0 )
    return -1.0;
 
  const int fromVertexNumber = fromVertex.vertex;
  const int toVertexNumber = toVertex.vertex;
 
  const int nPoints = numPoints();
  if ( fromVertexNumber < 0 || fromVertexNumber >= nPoints || toVertexNumber < 0 || toVertexNumber >= nPoints )
    return -1.0;
 
  if ( fromVertexNumber == toVertexNumber )
    return 0.0;
 
  const double *xData = mX.constData();
  const double *yData = mY.constData();
  double totalDistance = 0.0;
 
  // Start iteration from the arc containing fromVertex
  // Each arc starts at an even index (0, 2, 4, ...) and spans 3 vertices
  const int startArc = ( fromVertexNumber / 2 ) * 2;
 
  // Iterate through the arcs, accumulating distance between fromVertex and toVertex
  for ( int i = startArc; i < nPoints - 2; i += 2 )
  {
    // Arc segment from i to i+2, with curve point at i+1
    double x1 = xData[i]; // Start point
    double y1 = yData[i];
    double x2 = xData[i + 1]; // Curve point
    double y2 = yData[i + 1];
    double x3 = xData[i + 2]; // End point
    double y3 = yData[i + 2];
 
    // Check if both vertices are in this arc segment
    if ( fromVertexNumber >= i && toVertexNumber <= i + 2 )
    {
      if ( fromVertexNumber == i && toVertexNumber == i + 2 )
      {
        // Full arc from start to end
        return QgsGeometryUtilsBase::circleLength( x1, y1, x2, y2, x3, y3 );
      }
      else if ( fromVertexNumber == i && toVertexNumber == i + 1 )
      {
        // Arc from start point to curve point
        double centerX, centerY, radius;
        QgsGeometryUtilsBase::circleCenterRadius( x1, y1, x2, y2, x3, y3, radius, centerX, centerY );
        // Calculate arc length from vertex 0 to vertex 1
        return QgsGeometryUtilsBase::calculateArcLength( centerX, centerY, radius, x1, y1, x2, y2, x3, y3, 0, 1 );
      }
      else if ( fromVertexNumber == i + 1 && toVertexNumber == i + 2 )
      {
        // Arc from curve point to end point
        double centerX, centerY, radius;
        QgsGeometryUtilsBase::circleCenterRadius( x1, y1, x2, y2, x3, y3, radius, centerX, centerY );
        // Calculate arc length from vertex 1 to vertex 2
        return QgsGeometryUtilsBase::calculateArcLength( centerX, centerY, radius, x1, y1, x2, y2, x3, y3, 1, 2 );
      }
      else if ( fromVertexNumber == i + 1 && toVertexNumber == i + 1 )
      {
        return 0.0; // Same point
      }
    }
 
    // Handle cases where vertices span multiple segments
    bool startInThisSegment = ( fromVertexNumber >= i && fromVertexNumber <= i + 2 );
    bool endInThisSegment = ( toVertexNumber >= i && toVertexNumber <= i + 2 );
    bool segmentInRange = ( fromVertexNumber < i && toVertexNumber > i + 2 );
 
    if ( startInThisSegment && !endInThisSegment )
    {
      // fromVertex is in this segment, toVertex is beyond
      if ( fromVertexNumber == i )
        totalDistance += QgsGeometryUtilsBase::circleLength( x1, y1, x2, y2, x3, y3 );
      else if ( fromVertexNumber == i + 1 )
      {
        // From curve point to end of segment
        double centerX, centerY, radius;
        QgsGeometryUtilsBase::circleCenterRadius( x1, y1, x2, y2, x3, y3, radius, centerX, centerY );
        totalDistance += QgsGeometryUtilsBase::calculateArcLength( centerX, centerY, radius, x1, y1, x2, y2, x3, y3, 1, 2 );
      }
    }
    else if ( !startInThisSegment && endInThisSegment )
    {
      // fromVertex is before this segment, toVertex is in this segment
      if ( toVertexNumber == i + 1 )
      {
        // From start of segment to curve point
        double centerX, centerY, radius;
        QgsGeometryUtilsBase::circleCenterRadius( x1, y1, x2, y2, x3, y3, radius, centerX, centerY );
        totalDistance += QgsGeometryUtilsBase::calculateArcLength( centerX, centerY, radius, x1, y1, x2, y2, x3, y3, 0, 1 );
      }
      else if ( toVertexNumber == i + 2 )
        totalDistance += QgsGeometryUtilsBase::circleLength( x1, y1, x2, y2, x3, y3 );
      break;
    }
    else if ( segmentInRange )
    {
      // This entire segment is between fromVertex and toVertex
      totalDistance += QgsGeometryUtilsBase::circleLength( x1, y1, x2, y2, x3, y3 );
    }
  }
 
  return totalDistance;
}
 
 
QgsCircularString *QgsCircularString::reversed() const
{
  return qgis::down_cast< QgsCircularString *>( QgsSimpleCurve::reversed() );
}
 
QgsPoint *QgsCircularString::interpolatePoint( const double distance ) const
{
  if ( distance < 0 )
    return nullptr;
 
  double distanceTraversed = 0;
  const int totalPoints = numPoints();
  if ( totalPoints == 0 )
    return nullptr;
 
  Qgis::WkbType pointType = Qgis::WkbType::Point;
  if ( is3D() )
    pointType = Qgis::WkbType::PointZ;
  if ( isMeasure() )
    pointType = QgsWkbTypes::addM( pointType );
 
  const double *x = mX.constData();
  const double *y = mY.constData();
  const double *z = is3D() ? mZ.constData() : nullptr;
  const double *m = isMeasure() ? mM.constData() : nullptr;
 
  double prevX = *x++;
  double prevY = *y++;
  double prevZ = z ? *z++ : 0.0;
  double prevM = m ? *m++ : 0.0;
 
  if ( qgsDoubleNear( distance, 0.0 ) )
  {
    return new QgsPoint( pointType, prevX, prevY, prevZ, prevM );
  }
 
  for ( int i = 0; i < ( totalPoints - 2 ); i += 2 )
  {
    double x1 = prevX;
    double y1 = prevY;
    double z1 = prevZ;
    double m1 = prevM;
 
    double x2 = *x++;
    double y2 = *y++;
    double z2 = z ? *z++ : 0.0;
    double m2 = m ? *m++ : 0.0;
 
    double x3 = *x++;
    double y3 = *y++;
    double z3 = z ? *z++ : 0.0;
    double m3 = m ? *m++ : 0.0;
 
    const double segmentLength = QgsGeometryUtilsBase::circleLength( x1, y1, x2, y2, x3, y3 );
    if ( distance < distanceTraversed + segmentLength || qgsDoubleNear( distance, distanceTraversed + segmentLength ) )
    {
      // point falls on this segment - truncate to segment length if qgsDoubleNear test was actually > segment length
      const double distanceToPoint = std::min( distance - distanceTraversed, segmentLength );
      return new QgsPoint( QgsGeometryUtils::interpolatePointOnArc( QgsPoint( pointType, x1, y1, z1, m1 ), QgsPoint( pointType, x2, y2, z2, m2 ), QgsPoint( pointType, x3, y3, z3, m3 ), distanceToPoint ) );
    }
 
    distanceTraversed += segmentLength;
 
    prevX = x3;
    prevY = y3;
    prevZ = z3;
    prevM = m3;
  }
 
  return nullptr;
}
 
QgsCircularString *QgsCircularString::curveSubstring( double startDistance, double endDistance ) const
{
  if ( startDistance < 0 && endDistance < 0 )
    return createEmptyWithSameType();
 
  endDistance = std::max( startDistance, endDistance );
 
  const int totalPoints = numPoints();
  if ( totalPoints == 0 )
    return clone();
 
  QVector< QgsPoint > substringPoints;
  substringPoints.reserve( totalPoints );
 
  Qgis::WkbType pointType = Qgis::WkbType::Point;
  if ( is3D() )
    pointType = Qgis::WkbType::PointZ;
  if ( isMeasure() )
    pointType = QgsWkbTypes::addM( pointType );
 
  const double *x = mX.constData();
  const double *y = mY.constData();
  const double *z = is3D() ? mZ.constData() : nullptr;
  const double *m = isMeasure() ? mM.constData() : nullptr;
 
  double distanceTraversed = 0;
  double prevX = *x++;
  double prevY = *y++;
  double prevZ = z ? *z++ : 0.0;
  double prevM = m ? *m++ : 0.0;
  bool foundStart = false;
 
  if ( startDistance < 0 )
    startDistance = 0;
 
  for ( int i = 0; i < ( totalPoints - 2 ); i += 2 )
  {
    double x1 = prevX;
    double y1 = prevY;
    double z1 = prevZ;
    double m1 = prevM;
 
    double x2 = *x++;
    double y2 = *y++;
    double z2 = z ? *z++ : 0.0;
    double m2 = m ? *m++ : 0.0;
 
    double x3 = *x++;
    double y3 = *y++;
    double z3 = z ? *z++ : 0.0;
    double m3 = m ? *m++ : 0.0;
 
    bool addedSegmentEnd = false;
    const double segmentLength = QgsGeometryUtilsBase::circleLength( x1, y1, x2, y2, x3, y3 );
    if ( distanceTraversed <= startDistance && startDistance < distanceTraversed + segmentLength )
    {
      // start point falls on this segment
      const double distanceToStart = startDistance - distanceTraversed;
      const QgsPoint startPoint
        = QgsGeometryUtils::interpolatePointOnArc( QgsPoint( pointType, x1, y1, z1, m1 ), QgsPoint( pointType, x2, y2, z2, m2 ), QgsPoint( pointType, x3, y3, z3, m3 ), distanceToStart );
 
      // does end point also fall on this segment?
      const bool endPointOnSegment = distanceTraversed + segmentLength > endDistance;
      if ( endPointOnSegment )
      {
        const double distanceToEnd = endDistance - distanceTraversed;
        const double midPointDistance = ( distanceToEnd - distanceToStart ) * 0.5 + distanceToStart;
        substringPoints
          << startPoint
          << QgsGeometryUtils::interpolatePointOnArc( QgsPoint( pointType, x1, y1, z1, m1 ), QgsPoint( pointType, x2, y2, z2, m2 ), QgsPoint( pointType, x3, y3, z3, m3 ), midPointDistance )
          << QgsGeometryUtils::interpolatePointOnArc( QgsPoint( pointType, x1, y1, z1, m1 ), QgsPoint( pointType, x2, y2, z2, m2 ), QgsPoint( pointType, x3, y3, z3, m3 ), distanceToEnd );
        addedSegmentEnd = true;
      }
      else
      {
        const double midPointDistance = ( segmentLength - distanceToStart ) * 0.5 + distanceToStart;
        substringPoints
          << startPoint
          << QgsGeometryUtils::interpolatePointOnArc( QgsPoint( pointType, x1, y1, z1, m1 ), QgsPoint( pointType, x2, y2, z2, m2 ), QgsPoint( pointType, x3, y3, z3, m3 ), midPointDistance )
          << QgsPoint( pointType, x3, y3, z3, m3 );
        addedSegmentEnd = true;
      }
      foundStart = true;
    }
    if ( !addedSegmentEnd && foundStart && ( distanceTraversed + segmentLength > endDistance ) )
    {
      // end point falls on this segment
      const double distanceToEnd = endDistance - distanceTraversed;
      // add mid point, at half way along this arc, then add the interpolated end point
      substringPoints
        << QgsGeometryUtils::interpolatePointOnArc( QgsPoint( pointType, x1, y1, z1, m1 ), QgsPoint( pointType, x2, y2, z2, m2 ), QgsPoint( pointType, x3, y3, z3, m3 ), distanceToEnd / 2.0 )
 
        << QgsGeometryUtils::interpolatePointOnArc( QgsPoint( pointType, x1, y1, z1, m1 ), QgsPoint( pointType, x2, y2, z2, m2 ), QgsPoint( pointType, x3, y3, z3, m3 ), distanceToEnd );
    }
    else if ( !addedSegmentEnd && foundStart )
    {
      substringPoints << QgsPoint( pointType, x2, y2, z2, m2 ) << QgsPoint( pointType, x3, y3, z3, m3 );
    }
 
    prevX = x3;
    prevY = y3;
    prevZ = z3;
    prevM = m3;
    distanceTraversed += segmentLength;
    if ( distanceTraversed >= endDistance )
      break;
  }
 
  // start point is the last node
  if ( !foundStart && qgsDoubleNear( distanceTraversed, startDistance ) )
  {
    substringPoints << QgsPoint( pointType, prevX, prevY, prevZ, prevM ) << QgsPoint( pointType, prevX, prevY, prevZ, prevM ) << QgsPoint( pointType, prevX, prevY, prevZ, prevM );
  }
 
  auto result = std::make_unique< QgsCircularString >();
  result->setPoints( substringPoints );
  return result.release();
}