Add method to test whether 3 points are collinear

python/core/auto_generated/geometry/qgsgeometryutils.sip.in

@@ -797,6 +797,14 @@ Returns a weighted point inside the triangle denoted by the points (``aX``, ``aY
          - pointY: y-coordinate of generated point
 
 .. versionadded:: 3.10
+%End
+
+    static bool pointsAreCollinear( double x1, double y1, double x2, double y2, double x3, double y3, double epsilon );
+%Docstring
+Given the points (``x1``, ``y1``), (``x2``, ``y2``) and (``x3``, ``y3``) returns ``True`` if these
+points can be considered collinear with a specified tolerance.
+
+.. versionadded:: 3.32
 %End
 
  static bool setZValueFromPoints( const QgsPointSequence &points, QgsPoint &point ) /Deprecated/;

src/core/geometry/qgsgeometryutils.cpp

@@ -1864,6 +1864,11 @@ void QgsGeometryUtils::weightedPointInTriangle( const double aX, const double aY
   pointY = rBy + rCy + aY;
 }
 
+bool QgsGeometryUtils::pointsAreCollinear( double x1, double y1, double x2, double y2, double x3, double y3, double epsilon )
+{
+  return qgsDoubleNear( x1 * ( y2 - y3 ) + x2 * ( y3 - y1 ) + x3 * ( y1 - y2 ), 0, epsilon );
+};
+
 bool QgsGeometryUtils::transferFirstMValueToPoint( const QgsPointSequence &points, QgsPoint &point )
 {
   bool rc = false;

src/core/geometry/qgsgeometryutils.h

@@ -819,6 +819,14 @@ class CORE_EXPORT QgsGeometryUtils
     static void weightedPointInTriangle( double aX, double aY, double bX, double bY, double cX, double cY,
                                          double weightB, double weightC, double &pointX SIP_OUT, double &pointY SIP_OUT ) SIP_HOLDGIL;
 
+    /**
+     * Given the points (\a x1, \a y1), (\a x2, \a y2) and (\a x3, \a y3) returns TRUE if these
+     * points can be considered collinear with a specified tolerance.
+     *
+     * \since QGIS 3.32
+     */
+    static bool pointsAreCollinear( double x1, double y1, double x2, double y2, double x3, double y3, double epsilon );
+
     /**
      * A Z dimension is added to \a point if one of the point in the list
      * \a points is in 3D. Moreover, the Z value of \a point is updated

tests/src/core/geometry/testqgsgeometryutils.cpp

@@ -75,6 +75,7 @@ class TestQgsGeometryUtils: public QObject
     void testInterpolatePointOnLineByValue();
     void testPointOnLineWithDistance();
     void testPointFractionAlongLine();
+    void testPointsAreCollinear();
     void interpolatePointOnArc();
     void testSegmentizeArcHalfCircle();
     void testSegmentizeArcHalfCircleOtherDirection();
@@ -1386,6 +1387,20 @@ void TestQgsGeometryUtils::testPointFractionAlongLine()
   QGSCOMPARENEAR( QgsGeometryUtils::pointFractionAlongLine( 0, 10, 20, 10, 10, 10 ), 0.5, 0.00001 );
 }
 
+void TestQgsGeometryUtils::testPointsAreCollinear()
+{
+  QVERIFY( QgsGeometryUtils::pointsAreCollinear( 0, 10, 10, 10, 20, 10, 0.00001 ) );
+  QVERIFY( QgsGeometryUtils::pointsAreCollinear( 10, 10, 0, 10, 20, 10, 0.00001 ) );
+  QVERIFY( QgsGeometryUtils::pointsAreCollinear( 20, 10, 10, 10, 0, 10, 0.00001 ) );
+  QVERIFY( !QgsGeometryUtils::pointsAreCollinear( 20, 15, 10, 10, 0, 10, 0.00001 ) );
+  QVERIFY( !QgsGeometryUtils::pointsAreCollinear( 20, 10, 10, 15, 0, 10, 0.00001 ) );
+  QVERIFY( !QgsGeometryUtils::pointsAreCollinear( 20, 10, 10, 10, 0, 15, 0.00001 ) );
+  QVERIFY( QgsGeometryUtils::pointsAreCollinear( 10, 0, 10, 10, 10, 20, 0.00001 ) );
+  QVERIFY( QgsGeometryUtils::pointsAreCollinear( 10, 0, 10, 20, 10, 10, 0.00001 ) );
+  QVERIFY( QgsGeometryUtils::pointsAreCollinear( 10, 20, 10, 0, 10, 10, 0.00001 ) );
+  QVERIFY( !QgsGeometryUtils::pointsAreCollinear( 15, 20, 10, 10, 10, 20, 0.00001 ) );
+}
+
 void TestQgsGeometryUtils::interpolatePointOnArc()
 {
   QgsPoint p;