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Handle exact distances in curveSubstring
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Fixes #41081

These exact distances may be obtained with distance_to_vertex.

Before this change, the code considered the line segments as open
intervals, so that vertices could not ever be considered as the start
of a substring.  This change considers them as semi-open intervals
(closed at the beginning) instead. (With a special case when starting
the substring at the last vertex)

Before this change, vertices could not be considered as the end of a
substring, so an other loop was required, adding a duplicate node.

Similar behaviour is observed for QgsCircularString and corrected
similarly.

Double equality is performed as exact equality, because it does not
matter on which segment the start of the substring is. Except where
startDistance is -0.0, which is already handled before the for loop,
or when startDistance is at the last vertex.

(cherry picked from commit 5b2685d)
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@alkra @nyalldawson
alkra authored and nyalldawson committed Feb 19, 2021
1 parent 6c5b035 commit 2bf2246
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Showing 3 changed files with 36 additions and 26 deletions.
29 changes: 16 additions & 13 deletions src/core/geometry/qgscircularstring.cpp
View file
Expand Up @@ -1278,12 +1278,12 @@ QgsCircularString *QgsCircularString::curveSubstring( double startDistance, doub


endDistance = std::max( startDistance, endDistance ); endDistance = std::max( startDistance, endDistance );


double distanceTraversed = 0;
const int totalPoints = numPoints(); const int totalPoints = numPoints();
if ( totalPoints == 0 ) if ( totalPoints == 0 )
return clone(); return clone();


QVector< QgsPoint > substringPoints; QVector< QgsPoint > substringPoints;
substringPoints.reserve( totalPoints );


QgsWkbTypes::Type pointType = QgsWkbTypes::Point; QgsWkbTypes::Type pointType = QgsWkbTypes::Point;
if ( is3D() ) if ( is3D() )
Expand All @@ -1296,19 +1296,15 @@ QgsCircularString *QgsCircularString::curveSubstring( double startDistance, doub
const double *z = is3D() ? mZ.constData() : nullptr; const double *z = is3D() ? mZ.constData() : nullptr;
const double *m = isMeasure() ? mM.constData() : nullptr; const double *m = isMeasure() ? mM.constData() : nullptr;


double distanceTraversed = 0;
double prevX = *x++; double prevX = *x++;
double prevY = *y++; double prevY = *y++;
double prevZ = z ? *z++ : 0.0; double prevZ = z ? *z++ : 0.0;
double prevM = m ? *m++ : 0.0; double prevM = m ? *m++ : 0.0;
bool foundStart = false; bool foundStart = false;


if ( qgsDoubleNear( startDistance, 0.0 ) || startDistance < 0 ) if ( startDistance < 0 )
{ startDistance = 0;
substringPoints << QgsPoint( pointType, prevX, prevY, prevZ, prevM );
foundStart = true;
}

substringPoints.reserve( totalPoints );


for ( int i = 0; i < ( totalPoints - 2 ) ; i += 2 ) for ( int i = 0; i < ( totalPoints - 2 ) ; i += 2 )
{ {
Expand All @@ -1329,7 +1325,7 @@ QgsCircularString *QgsCircularString::curveSubstring( double startDistance, doub


bool addedSegmentEnd = false; bool addedSegmentEnd = false;
const double segmentLength = QgsGeometryUtils::circleLength( x1, y1, x2, y2, x3, y3 ); const double segmentLength = QgsGeometryUtils::circleLength( x1, y1, x2, y2, x3, y3 );
if ( distanceTraversed < startDistance && distanceTraversed + segmentLength > startDistance ) if ( distanceTraversed <= startDistance && startDistance < distanceTraversed + segmentLength )
{ {
// start point falls on this segment // start point falls on this segment
const double distanceToStart = startDistance - distanceTraversed; const double distanceToStart = startDistance - distanceTraversed;
Expand Down Expand Up @@ -1383,14 +1379,21 @@ QgsCircularString *QgsCircularString::curveSubstring( double startDistance, doub
<< QgsPoint( pointType, x3, y3, z3, m3 ); << QgsPoint( pointType, x3, y3, z3, m3 );
} }


distanceTraversed += segmentLength;
if ( distanceTraversed > endDistance )
break;

prevX = x3; prevX = x3;
prevY = y3; prevY = y3;
prevZ = z3; prevZ = z3;
prevM = m3; 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 );
} }


std::unique_ptr< QgsCircularString > result = qgis::make_unique< QgsCircularString >(); std::unique_ptr< QgsCircularString > result = qgis::make_unique< QgsCircularString >();
Expand Down
29 changes: 16 additions & 13 deletions src/core/geometry/qgslinestring.cpp
View file
Expand Up @@ -1030,12 +1030,12 @@ QgsLineString *QgsLineString::curveSubstring( double startDistance, double endDi


endDistance = std::max( startDistance, endDistance ); endDistance = std::max( startDistance, endDistance );


double distanceTraversed = 0;
const int totalPoints = numPoints(); const int totalPoints = numPoints();
if ( totalPoints == 0 ) if ( totalPoints == 0 )
return clone(); return clone();


QVector< QgsPoint > substringPoints; QVector< QgsPoint > substringPoints;
substringPoints.reserve( totalPoints );


QgsWkbTypes::Type pointType = QgsWkbTypes::Point; QgsWkbTypes::Type pointType = QgsWkbTypes::Point;
if ( is3D() ) if ( is3D() )
Expand All @@ -1048,19 +1048,15 @@ QgsLineString *QgsLineString::curveSubstring( double startDistance, double endDi
const double *z = is3D() ? mZ.constData() : nullptr; const double *z = is3D() ? mZ.constData() : nullptr;
const double *m = isMeasure() ? mM.constData() : nullptr; const double *m = isMeasure() ? mM.constData() : nullptr;


double distanceTraversed = 0;
double prevX = *x++; double prevX = *x++;
double prevY = *y++; double prevY = *y++;
double prevZ = z ? *z++ : 0.0; double prevZ = z ? *z++ : 0.0;
double prevM = m ? *m++ : 0.0; double prevM = m ? *m++ : 0.0;
bool foundStart = false; bool foundStart = false;


if ( qgsDoubleNear( startDistance, 0.0 ) || startDistance < 0 ) if ( startDistance < 0 )
{ startDistance = 0;
substringPoints << QgsPoint( pointType, prevX, prevY, prevZ, prevM );
foundStart = true;
}

substringPoints.reserve( totalPoints );


for ( int i = 1; i < totalPoints; ++i ) for ( int i = 1; i < totalPoints; ++i )
{ {
Expand All @@ -1070,7 +1066,8 @@ QgsLineString *QgsLineString::curveSubstring( double startDistance, double endDi
double thisM = m ? *m++ : 0.0; double thisM = m ? *m++ : 0.0;


const double segmentLength = std::sqrt( ( thisX - prevX ) * ( thisX - prevX ) + ( thisY - prevY ) * ( thisY - prevY ) ); const double segmentLength = std::sqrt( ( thisX - prevX ) * ( thisX - prevX ) + ( thisY - prevY ) * ( thisY - prevY ) );
if ( distanceTraversed < startDistance && distanceTraversed + segmentLength > startDistance )
if ( distanceTraversed <= startDistance && startDistance < distanceTraversed + segmentLength )
{ {
// start point falls on this segment // start point falls on this segment
const double distanceToStart = startDistance - distanceTraversed; const double distanceToStart = startDistance - distanceTraversed;
Expand Down Expand Up @@ -1100,14 +1097,20 @@ QgsLineString *QgsLineString::curveSubstring( double startDistance, double endDi
substringPoints << QgsPoint( pointType, thisX, thisY, thisZ, thisM ); substringPoints << QgsPoint( pointType, thisX, thisY, thisZ, thisM );
} }


distanceTraversed += segmentLength;
if ( distanceTraversed > endDistance )
break;

prevX = thisX; prevX = thisX;
prevY = thisY; prevY = thisY;
prevZ = thisZ; prevZ = thisZ;
prevM = thisM; prevM = thisM;
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 );
} }


return new QgsLineString( substringPoints ); return new QgsLineString( substringPoints );
Expand Down
4 changes: 4 additions & 0 deletions tests/src/core/testqgsgeometry.cpp
View file
Expand Up @@ -2846,6 +2846,8 @@ void TestQgsGeometry::circularString()
QCOMPARE( substringResult->asWkt( 2 ), QStringLiteral( "CircularStringZM (13.51 -0.98 13 14, 14.01 -1 13.03 14.03, 14.5 -0.9 14.65 15.65)" ) ); QCOMPARE( substringResult->asWkt( 2 ), QStringLiteral( "CircularStringZM (13.51 -0.98 13 14, 14.01 -1 13.03 14.03, 14.5 -0.9 14.65 15.65)" ) );
substringResult.reset( substring.curveSubstring( 5, 1000 ) ); substringResult.reset( substring.curveSubstring( 5, 1000 ) );
QCOMPARE( substringResult->asWkt( 2 ), QStringLiteral( "CircularStringZM (13.51 -0.98 13 14, 15.19 -0.53 17.2 18.2, 16 1 23 24)" ) ); QCOMPARE( substringResult->asWkt( 2 ), QStringLiteral( "CircularStringZM (13.51 -0.98 13 14, 15.19 -0.53 17.2 18.2, 16 1 23 24)" ) );
substringResult.reset( substring.curveSubstring( QgsGeometryUtils::distanceToVertex( substring, QgsVertexId( 0, 0, 2 ) ), QgsGeometryUtils::distanceToVertex( substring, QgsVertexId( 0, 0, 4 ) ) ) );
QCOMPARE( substringResult->asWkt( 2 ), QStringLiteral( "CircularStringZM (12 0 13 14, 14.36 -0.94 14.19 15.19, 16 1 23 24)" ) );


substring.setPoints( QgsPointSequence() << QgsPoint( 10, 0, 1 ) << QgsPoint( 11, 1, 3 ) << QgsPoint( 12, 0, 13 ) substring.setPoints( QgsPointSequence() << QgsPoint( 10, 0, 1 ) << QgsPoint( 11, 1, 3 ) << QgsPoint( 12, 0, 13 )
<< QgsPoint( 14, -1, 13 ) << QgsPoint( 16, 1, 23 ) ); << QgsPoint( 14, -1, 13 ) << QgsPoint( 16, 1, 23 ) );
Expand Down Expand Up @@ -4930,6 +4932,8 @@ void TestQgsGeometry::lineString()
QCOMPARE( substringResult->asWkt( 2 ), QStringLiteral( "LineStringZM (11 3 4 5, 11 12 13 14, 111 12 23 24)" ) ); QCOMPARE( substringResult->asWkt( 2 ), QStringLiteral( "LineStringZM (11 3 4 5, 11 12 13 14, 111 12 23 24)" ) );
substringResult.reset( substring.curveSubstring( 1, 20 ) ); substringResult.reset( substring.curveSubstring( 1, 20 ) );
QCOMPARE( substringResult->asWkt( 2 ), QStringLiteral( "LineStringZM (11 3 4 5, 11 12 13 14, 21 12 14 15)" ) ); QCOMPARE( substringResult->asWkt( 2 ), QStringLiteral( "LineStringZM (11 3 4 5, 11 12 13 14, 21 12 14 15)" ) );
substringResult.reset( substring.curveSubstring( QgsGeometryUtils::distanceToVertex( substring, QgsVertexId( 0, 0, 1 ) ), QgsGeometryUtils::distanceToVertex( substring, QgsVertexId( 0, 0, 2 ) ) ) );
QCOMPARE( substringResult->asWkt( 2 ), QStringLiteral( "LineStringZM (11 12 13 14, 111 12 23 24)" ) );
substring.setPoints( QgsPointSequence() << QgsPoint( 11, 2, 3, 0, QgsWkbTypes::PointZ ) << QgsPoint( 11, 12, 13, 0, QgsWkbTypes::PointZ ) << QgsPoint( 111, 12, 23, 0, QgsWkbTypes::PointZ ) ); substring.setPoints( QgsPointSequence() << QgsPoint( 11, 2, 3, 0, QgsWkbTypes::PointZ ) << QgsPoint( 11, 12, 13, 0, QgsWkbTypes::PointZ ) << QgsPoint( 111, 12, 23, 0, QgsWkbTypes::PointZ ) );
substringResult.reset( substring.curveSubstring( 1, 20 ) ); substringResult.reset( substring.curveSubstring( 1, 20 ) );
QCOMPARE( substringResult->asWkt( 2 ), QStringLiteral( "LineStringZ (11 3 4, 11 12 13, 21 12 14)" ) ); QCOMPARE( substringResult->asWkt( 2 ), QStringLiteral( "LineStringZ (11 3 4, 11 12 13, 21 12 14)" ) );
Expand Down

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