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qgsvectorlayerprofilegenerator: Fix intersection for collinear polygons #66432

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qgsvectorlayerprofilegenerator: Fix intersection for collinear polygons #66432

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19 changes: 14 additions & 5 deletions src/core/vector/qgsvectorlayerprofilegenerator.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1479,7 +1479,7 @@ bool QgsVectorLayerProfileGenerator::generateProfileForPolygons()
if ( triangleIsCollinearInXYPlane( triangle ) )
{
wasCollinear = true;
const QgsLineString *ring = qgsgeometry_cast< const QgsLineString * >( polygon->exteriorRing() );
const QgsLineString *ring = qgsgeometry_cast< const QgsLineString * >( triangle->exteriorRing() );

QString lastError;
if ( const QgsLineString *ls = qgsgeometry_cast< const QgsLineString * >( mProfileCurve.get() ) )
Expand All @@ -1490,24 +1490,33 @@ bool QgsVectorLayerProfileGenerator::generateProfileForPolygons()
const QgsPoint p2 = ls->pointN( curveSegmentIndex + 1 );

QgsPoint intersectionPoint;
bool intersectionFound = false;
double minZ = std::numeric_limits< double >::max();
double maxZ = std::numeric_limits< double >::lowest();

for ( auto vertexPair : std::array<std::pair<int, int>, 3> { { { 0, 1 }, { 1, 2 }, { 2, 0 } } } )
{
bool isIntersection = false;
if ( QgsGeometryUtils::segmentIntersection( ring->pointN( vertexPair.first ), ring->pointN( vertexPair.second ), p1, p2, intersectionPoint, isIntersection ) )
QgsPoint edgeIntersectionPoint;
if ( QgsGeometryUtils::segmentIntersection( ring->pointN( vertexPair.first ), ring->pointN( vertexPair.second ), p1, p2, edgeIntersectionPoint, isIntersection ) )
{
if ( !edgeIntersectionPoint.isEmpty() && !intersectionFound )
{
intersectionPoint = edgeIntersectionPoint;
intersectionFound = true;
}


const double fraction = QgsGeometryUtilsBase::pointFractionAlongLine(
ring->xAt( vertexPair.first ), ring->yAt( vertexPair.first ), ring->xAt( vertexPair.second ), ring->yAt( vertexPair.second ), intersectionPoint.x(), intersectionPoint.y()
ring->xAt( vertexPair.first ), ring->yAt( vertexPair.first ), ring->xAt( vertexPair.second ), ring->yAt( vertexPair.second ), edgeIntersectionPoint.x(), edgeIntersectionPoint.y()
);
const double intersectionZ = ring->zAt( vertexPair.first ) + ( ring->zAt( vertexPair.second ) - ring->zAt( vertexPair.first ) ) * fraction;
double intersectionZ = ring->zAt( vertexPair.first ) + ( ring->zAt( vertexPair.second ) - ring->zAt( vertexPair.first ) ) * fraction;
minZ = std::min( minZ, intersectionZ );
maxZ = std::max( maxZ, intersectionZ );
}
}

if ( !intersectionPoint.isEmpty() )
if ( intersectionFound )
{
// need z?
mResults->mRawPoints.append( intersectionPoint );
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30 changes: 30 additions & 0 deletions tests/src/python/test_qgsvectorlayerprofilegenerator.py
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Expand Up @@ -898,6 +898,36 @@ def testPolygonGenerationAbsolute(self):
self.assertAlmostEqual(results.zRange().lower(), 15.0, 2)
self.assertAlmostEqual(results.zRange().upper(), 22.5000, 2)

def testPolygonGenerationFollowingLinestringZExactly(self):
vl = QgsVectorLayer("PolygonZ?crs=EPSG:3857", "polygon", "memory")
self.assertTrue(vl.isValid())

polygon_wkt = "Polygon Z ((547405.88 6150237.19 0, 547405.88 6150237.19 5, 547413.39 6150203.24 5, 547413.39 6150203.24 0, 547405.88 6150237.19 0))"

@rouault rouault Jun 10, 2026

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those "random" looking coordinates are difficult to reason with. If there was a way of coming with simple looking coordinates, that might help (no strong requirement, just asking in case it is not too difficult)

@ptitjano ptitjano Jun 10, 2026

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No strong opinion. I just tried to stay in line with other unit test which use similar "random" coordinates.

feature = QgsFeature()
feature.setGeometry(QgsGeometry.fromWkt(polygon_wkt))
self.assertTrue(vl.dataProvider().addFeature(feature))

vl.elevationProperties().setClamping(Qgis.AltitudeClamping.Absolute)

curve = QgsLineString()
curve.fromWkt(
"LineString (547394.297515 6150220.613784, 547416.10922 6150225.219982)"
)
req = QgsProfileRequest(curve)
req.setCrs(QgsCoordinateReferenceSystem("EPSG:3857"))

generator = vl.createProfileGenerator(req)
self.assertTrue(generator.generateProfile())
results = generator.takeResults()

self.assertEqual(
self.round_dict(results.distanceToHeightMap(), 1, 1),
{14.9: 5.0},
)

self.assertAlmostEqual(results.zRange().lower(), 0.0, 2)
self.assertAlmostEqual(results.zRange().upper(), 5.0, 2)

def testPolygonGenerationTerrain(self):
vl = QgsVectorLayer("PolygonZ?crs=EPSG:27700", "lines", "memory")
self.assertTrue(vl.isValid())
Expand Down
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