[FEATURE][expression] Add a to_decimal() function to convert degree/minute/second strings

resources/function_help/json/to_decimal

@@ -0,0 +1,12 @@
+{
+  "name": "to_decimal",
+  "type": "function",
+  "groups": ["Conversions"],
+  "description": "Converts a degree, minute, second coordinate to its decimal equivalent.",
+  "arguments": [
+    {"arg":"value","description":"A degree, minute, second string."}
+  ],
+    "examples": [
+    { "expression":"to_decimal('6°21\\'16.445')", "returns":"6.3545680555"}
+  ]
+}

src/core/expression/qgsexpressionfunction.cpp

@@ -17,6 +17,7 @@
 #include <random>
 
 #include "qgscoordinateformatter.h"
+#include "qgscoordinateutils.h"
 #include "qgsexpressionfunction.h"
 #include "qgsexpressionutils.h"
 #include "qgsexpressionnodeimpl.h"
@@ -2100,6 +2101,15 @@ static QVariant fcnToDegreeMinute( const QVariantList &values, const QgsExpressi
   return floatToDegreeFormat( format, values, context, parent, node );
 }
 
+static QVariant fcnToDecimal( const QVariantList &values, const QgsExpressionContext *, QgsExpression *parent, const QgsExpressionNodeFunction * )
+{
+  double value = 0.0;
+  bool ok = false;
+  value = QgsCoordinateUtils::dmsToDecimal( QgsExpressionUtils::getStringValue( values.at( 0 ), parent ), &ok );
+
+  return ok ? QVariant( value ) : QVariant();
+}
+
 static QVariant fcnToDegreeMinuteSecond( const QVariantList &values, const QgsExpressionContext *context, QgsExpression *parent, const QgsExpressionNodeFunction *node )
 {
   QgsCoordinateFormatter::Format format = QgsCoordinateFormatter::FormatDegreesMinutesSeconds;
@@ -5737,6 +5747,7 @@ const QList<QgsExpressionFunction *> &QgsExpression::Functions()
         << new QgsStaticExpressionFunction( QStringLiteral( "to_interval" ), QgsExpressionFunction::ParameterList() << QgsExpressionFunction::Parameter( QStringLiteral( "value" ) ), fcnToInterval, QStringList() << QStringLiteral( "Conversions" ) << QStringLiteral( "Date and Time" ), QString(), false, QSet<QString>(), false, QStringList() << QStringLiteral( "tointerval" ) )
         << new QgsStaticExpressionFunction( QStringLiteral( "to_dm" ), QgsExpressionFunction::ParameterList() << QgsExpressionFunction::Parameter( QStringLiteral( "value" ) ) << QgsExpressionFunction::Parameter( QStringLiteral( "axis" ) ) << QgsExpressionFunction::Parameter( QStringLiteral( "precision" ) ) << QgsExpressionFunction::Parameter( QStringLiteral( "formatting" ), true ), fcnToDegreeMinute, QStringLiteral( "Conversions" ), QString(), false, QSet<QString>(), false, QStringList() << QStringLiteral( "todm" ) )
         << new QgsStaticExpressionFunction( QStringLiteral( "to_dms" ), QgsExpressionFunction::ParameterList() << QgsExpressionFunction::Parameter( QStringLiteral( "value" ) ) << QgsExpressionFunction::Parameter( QStringLiteral( "axis" ) ) << QgsExpressionFunction::Parameter( QStringLiteral( "precision" ) ) << QgsExpressionFunction::Parameter( QStringLiteral( "formatting" ), true ), fcnToDegreeMinuteSecond, QStringLiteral( "Conversions" ), QString(), false, QSet<QString>(), false, QStringList() << QStringLiteral( "todms" ) )
+        << new QgsStaticExpressionFunction( QStringLiteral( "to_decimal" ), QgsExpressionFunction::ParameterList() << QgsExpressionFunction::Parameter( QStringLiteral( "value" ) ), fcnToDecimal, QStringLiteral( "Conversions" ), QString(), false, QSet<QString>(), false, QStringList() << QStringLiteral( "todecimal" ) )
         << new QgsStaticExpressionFunction( QStringLiteral( "coalesce" ), -1, fcnCoalesce, QStringLiteral( "Conditionals" ), QString(), false, QSet<QString>(), false, QStringList(), true )
         << new QgsStaticExpressionFunction( QStringLiteral( "nullif" ), QgsExpressionFunction::ParameterList() << QgsExpressionFunction::Parameter( QStringLiteral( "value1" ) ) << QgsExpressionFunction::Parameter( QStringLiteral( "value2" ) ), fcnNullIf, QStringLiteral( "Conditionals" ) )
         << new QgsStaticExpressionFunction( QStringLiteral( "if" ), QgsExpressionFunction::ParameterList() << QgsExpressionFunction::Parameter( QStringLiteral( "condition" ) ) << QgsExpressionFunction::Parameter( QStringLiteral( "result_when_true" ) )  << QgsExpressionFunction::Parameter( QStringLiteral( "result_when_false" ) ), fcnIf, QStringLiteral( "Conditionals" ), QString(), false, QSet<QString>(), true )

src/core/qgscoordinateutils.cpp

@@ -106,4 +106,60 @@ QString QgsCoordinateUtils::formatCoordinateForProject( QgsProject *project, con
   }
 }
 
+double QgsCoordinateUtils::dmsToDecimal( const QString &string, bool *ok )
+{
+  const QString negative( QStringLiteral( "swSW-" ) );
+  double value = 0.0;
+  bool okValue = false;
+
+  if ( ok )
+  {
+    *ok = false;
+  }
+  else
+  {
+    ok = &okValue;
+  }
+
+  QRegularExpression dms( "^\\s*(?:([-+nsew])\\s*)?(\\d{1,3})(?:[^0-9.]+([0-5]?\\d))?[^0-9.]+([0-5]?\\d(?:\\.\\d+)?)[^0-9.]*?([-+nsew])?\\s*$", QRegularExpression::CaseInsensitiveOption );
+  QRegularExpressionMatch match = dms.match( string.trimmed() );
+  if ( match.hasMatch() )
+  {
+    QString dms1 = match.captured( 2 );
+    QString dms2 = match.captured( 3 );
+    QString dms3 = match.captured( 4 );
+
+    double v = dms3.toDouble( ok );
+    if ( *ok == false )
+      return value;
+    // Allow for Degrees/minutes format as well as DMS
+    if ( !dms2.isEmpty() )
+    {
+      v = dms2.toInt( ok ) + v / 60.0;
+      if ( *ok == false )
+        return value;
+    }
+    v = dms1.toInt( ok ) + v / 60.0;
+    if ( *ok == false )
+      return value;
+
+    QString sign1 = match.captured( 1 );
+    QString sign2 = match.captured( 5 );
+
+    if ( sign1.isEmpty() )
+    {
+      value = !sign2.isEmpty() && negative.contains( sign2 ) ? -v : v;
+    }
+    else if ( sign2.isEmpty() )
+    {
+      value = !sign1.isEmpty() && negative.contains( sign1 ) ? -v : v;
+    }
+    else
+    {
+      *ok = false;
+    }
+  }
+  return value;
+}
+
 ///@endcond

src/core/qgscoordinateutils.h

@@ -67,6 +67,14 @@ class CORE_EXPORT QgsCoordinateUtils
      */
     Q_INVOKABLE static QString formatCoordinateForProject( QgsProject *project, const QgsPointXY &point, const QgsCoordinateReferenceSystem &destCrs, int precision );
 
+    /**
+     * Converts a degree minute second coordinate string to its decimal equivalent.
+     * \param string degree minute second string to convert
+     * \returns Double decimal value
+     * \since QGIS 3.16
+     */
+    Q_INVOKABLE static double dmsToDecimal( const QString &string, bool *ok );
+
 };
 
 

tests/src/core/testqgsexpression.cpp

@@ -869,6 +869,8 @@ class TestQgsExpression: public QObject
       QTest::newRow( "Y coordinate to degree minute second with suffix" ) << "to_dms(6.3545681,'y',2,'suffix')" << false << QVariant( "6°21′16.45″N" );
       QTest::newRow( "Y coordinate to degree minute second without formatting" ) << "to_dms(6.3545681,'y',2,'')" << false << QVariant( "6°21′16.45″" );
       QTest::newRow( "Y coordinate to degree minute second" ) << "to_dms(6.3545681,'y',2)" << false << QVariant( "6°21′16.45″" );
+      QTest::newRow( "degree minute second string to decimal" ) << "to_decimal('6°21′16.45″N')" << false << QVariant( 6.35456944444 );
+      QTest::newRow( "wrong degree minute second string to decimal" ) << "to_decimal('qgis')" << false << QVariant();
 
       // geometry functions
       QTest::newRow( "geom_to_wkb" ) << "geom_to_wkt(geom_from_wkb(geom_to_wkb(make_point(4,5))))" << false << QVariant( "Point (4 5)" );