Fix logarithmic classification with narrow ranges

Fix #45454
qgis · Feb 9, 2022 · ea93537 · ea93537
1 parent 2db7926
commit ea93537
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Showing 2 changed files with 36 additions and 4 deletions.
diff --git a/src/core/classification/qgsclassificationlogarithmic.cpp b/src/core/classification/qgsclassificationlogarithmic.cpp
@@ -94,15 +94,27 @@ QList<double> QgsClassificationLogarithmic::calculateBreaks( double &minimum, do
   }
 
   // get the min/max in log10 scale
-  const double logMin = std::floor( std::log10( positiveMinimum ) );
+  const double actualLogMin { std::log10( positiveMinimum ) };
+  double logMin = std::floor( actualLogMin );
   const double logMax = std::ceil( std::log10( maximum ) );
 
   // calculate pretty breaks
-  breaks.append( QgsSymbolLayerUtils::prettyBreaks( logMin, logMax, nclasses ) );
+  QList<double> prettyBreaks { QgsSymbolLayerUtils::prettyBreaks( logMin, logMax, nclasses ) };
+
+  // If case the first class greater than the actual log min increase the minimum log
+  while ( ! prettyBreaks.isEmpty() && prettyBreaks.first() < actualLogMin )
+  {
+    logMin += 1.0;
+    prettyBreaks = QgsSymbolLayerUtils::prettyBreaks( logMin, logMax, nclasses );
+  }
+
+  breaks.append( prettyBreaks );
 
   // create the value
   for ( int i = 0; i < breaks.count(); i++ )
+  {
     breaks[i] = std::pow( 10, breaks.at( i ) );
+  }
 
   return breaks;
 }
@@ -121,7 +133,7 @@ QString QgsClassificationLogarithmic::valueToLabel( double value ) const
     }
     else
     {
-      return QString( QStringLiteral( "10^%1" ) ).arg( std::log10( value ) );
+      return QString( QStringLiteral( "10^%L1" ) ).arg( std::log10( value ) );
     }
   }
 }
@@ -142,7 +154,7 @@ QString QgsClassificationLogarithmic::labelForRange( double lowerValue, double u
       break;
   }
 
-  return labelFormat().arg( lowerLabel ).arg( upperLabel );
+  return labelFormat().arg( lowerLabel, upperLabel );
 }
 
 bool QgsClassificationLogarithmic::valuesRequired() const

diff --git a/tests/src/python/test_qgsclassificationmethod.py b/tests/src/python/test_qgsclassificationmethod.py
@@ -70,6 +70,26 @@ def testQgsClassificationLogarithmic(self):
 
         self.assertEqual(len(m.classes(vl, 'value', 4)), 4)
 
+    def testQgsClassificationLogarithmicCloseMinimum(self):
+        """See issue GH #45454: Incorrect scale range legend after applying
+        logarithmic graduated symbology to a vector layer"""
+
+        values = [0.009900019065438,
+                  0.010851322017611,
+                  0.01755707784994,
+                  0.031925433036994,
+                  0.046422733606398]
+
+        vl = createMemoryLayer(values)
+
+        m = QgsClassificationLogarithmic()
+        r = m.classes(vl, 'value', 4)
+
+        classes = [(c.lowerBound(), c.upperBound()) for c in r]
+
+        for l, h in classes:
+            self.assertLess(l, h)
+
     def testQgsClassificationLogarithmic_FilterZeroNeg(self):
         values = [-2, 0, 1, 7, 66, 555, 4444]
         vl = createMemoryLayer(values)