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# qgis / QGIS

nyalldawson committed May 13, 2013
 @@ -0,0 +1,19 @@

clamp() function

Restricts an input value to a specified range.

Syntax

clamp(minimum,input,maximum)

Arguments

minimum → The smallest value input is allowed to take.
input → a value which will be restricted to the range specified by minimum and maximum.
maximum → The largest value input is allowed to take.

Example

clamp(1,5,10) → 5 (input is between 1 and 10 so is returned unchanged)
clamp(1,0,10) → 1 (input is less than minimum value of 1, so function returns 1)
clamp(1,11,10) → 10 (input is greater than maximum value of 10, so function returns 11)
 @@ -0,0 +1,28 @@

scale_exp() function

Transforms a given value from an input domain to an output range using an exponential curve. This function can be used to ease values in or out of the specified output range.

Syntax

scale_exp(val,domain_min,domain_max,range_min,range_max,exponent)

Arguments

val → is a value in the input domain. The function will return a corresponding scaled value in the output range.
domain_min, domain_max → specify the input domain, the smallest and largest values the input val should take.
range_min, range_max → specify the output range, the smallest and largest values which should be output by the function.
exponent → a positive value (greater than 0), which dictates the way input values are mapped to the output range. Large exponents will cause the output values to 'ease in', starting slowly before accelerating as the input values approach the domain maximum. Smaller exponents (less than 1) will cause output values to 'ease out', where the mapping starts quickly but slows as it approaches the domain maximum.

Example

Easing in, using an exponent of 2:
scale_exp(5,0,10,0,100,2) → 25
scale_exp(7.5,0,10,0,100,2) → 56.25
scale_exp(9.5,0,10,0,100,2) → 90.25

Easing out, using an exponent of 0.5:
scale_exp(3,0,10,0,100,0.5) → 54.772
scale_exp(6,0,10,0,100,0.5) → 77.459
scale_exp(9,0,10,0,100,0.5) → 94.868
 @@ -442,29 +442,69 @@ static QVariant fcnRnd( const QVariantList& values, QgsFeature* , QgsExpression* static QVariant fcnLinearScale( const QVariantList& values, QgsFeature* , QgsExpression* parent ) { double val = getDoubleValue( values.at( 0 ), parent ); double domain_min = getDoubleValue( values.at( 1 ), parent ); double domain_max = getDoubleValue( values.at( 2 ), parent ); double range_min = getDoubleValue( values.at( 3 ), parent ); double range_max = getDoubleValue( values.at( 4 ), parent ); double domainMin = getDoubleValue( values.at( 1 ), parent ); double domainMax = getDoubleValue( values.at( 2 ), parent ); double rangeMin = getDoubleValue( values.at( 3 ), parent ); double rangeMax = getDoubleValue( values.at( 4 ), parent ); if ( domainMin >= domainMax ) { parent->setEvalErrorString( QObject::tr( "Domain max must be greater than domain min" ) ); return QVariant(); } // outside of domain? if ( val >= domain_max ) if ( val >= domainMax ) { return range_max; return rangeMax; } else if ( val <= domain_min ) else if ( val <= domainMin ) { return range_min; return rangeMin; } // calculate linear scale double m = ( range_max - range_min ) / ( domain_max - domain_min ); double c = range_min - ( domain_min * m ); double m = ( rangeMax - rangeMin ) / ( domainMax - domainMin ); double c = rangeMin - ( domainMin * m ); // Return linearly scaled value return QVariant( m * val + c ); } static QVariant fcnExpScale( const QVariantList& values, QgsFeature* , QgsExpression* parent ) { double val = getDoubleValue( values.at( 0 ), parent ); double domainMin = getDoubleValue( values.at( 1 ), parent ); double domainMax = getDoubleValue( values.at( 2 ), parent ); double rangeMin = getDoubleValue( values.at( 3 ), parent ); double rangeMax = getDoubleValue( values.at( 4 ), parent ); double exponent = getDoubleValue( values.at( 5 ), parent ); if ( domainMin >= domainMax ) { parent->setEvalErrorString( QObject::tr( "Domain max must be greater than domain min" ) ); return QVariant(); } if ( exponent <= 0 ) { parent->setEvalErrorString( QObject::tr( "Exponent must be greater than 0" ) ); return QVariant(); } // outside of domain? if ( val >= domainMax ) { return rangeMax; } else if ( val <= domainMin ) { return rangeMin; } // Return exponentially scaled value return QVariant((( rangeMax - rangeMin ) / pow( domainMax - domainMin, exponent ) ) * pow( val - domainMin, exponent ) + rangeMin ); } static QVariant fcnMax( const QVariantList& values, QgsFeature* , QgsExpression *parent ) { //initially set max as first value @@ -501,6 +541,27 @@ static QVariant fcnMin( const QVariantList& values, QgsFeature* , QgsExpression return QVariant( minVal ); } static QVariant fcnClamp( const QVariantList& values, QgsFeature* , QgsExpression* parent ) { double minValue = getDoubleValue( values.at( 0 ), parent ); double testValue = getDoubleValue( values.at( 1 ), parent ); double maxValue = getDoubleValue( values.at( 2 ), parent ); // force testValue to sit inside the range specified by the min and max value if ( testValue <= minValue ) { return QVariant( minValue ); } else if ( testValue >= maxValue ) { return QVariant( maxValue ); } else { return QVariant( testValue ); } } static QVariant fcnFloor( const QVariantList& values, QgsFeature* , QgsExpression* parent ) { double x = getDoubleValue( values.at( 0 ), parent ); @@ -1342,8 +1403,8 @@ const QStringList &QgsExpression::BuiltinFunctions() << "abs" << "sqrt" << "cos" << "sin" << "tan" << "asin" << "acos" << "atan" << "atan2" << "exp" << "ln" << "log10" << "log" << "round" << "rand" << "randf" << "max" << "min" << "scale_linear" << "floor" << "ceil" << "round" << "rand" << "randf" << "max" << "min" << "clamp" << "scale_linear" << "scale_exp" << "floor" << "ceil" << "toint" << "toreal" << "tostring" << "todatetime" << "todate" << "totime" << "tointerval" << "coalesce" << "regexp_match" << "\$now" << "age" << "year" @@ -1389,7 +1450,9 @@ const QList &QgsExpression::Functions() << new StaticFunction( "randf", 2, fcnRndF, QObject::tr( "Math" ) ) << new StaticFunction( "max", -1, fcnMax, QObject::tr( "Math" ) ) << new StaticFunction( "min", -1, fcnMin, QObject::tr( "Math" ) ) << new StaticFunction( "clamp", 3, fcnClamp, QObject::tr( "Math" ) ) << new StaticFunction( "scale_linear", 5, fcnLinearScale, QObject::tr( "Math" ) ) << new StaticFunction( "scale_exp", 6, fcnExpScale, QObject::tr( "Math" ) ) << new StaticFunction( "floor", 1, fcnFloor, QObject::tr( "Math" ) ) << new StaticFunction( "ceil", 1, fcnCeil, QObject::tr( "Math" ) ) << new StaticFunction( "\$pi", 0, fcnPi, QObject::tr( "Math" ) )
 @@ -260,6 +260,9 @@ class TestQgsExpression: public QObject QTest::newRow( "max(1,3.5,-2.1)" ) << "max(1,3.5,-2.1)" << false << QVariant( 3.5 ); QTest::newRow( "min(-1.5)" ) << "min(-1.5)" << false << QVariant( -1.5 ); QTest::newRow( "min(-16.6,3.5,-2.1)" ) << "min(-16.6,3.5,-2.1)" << false << QVariant( -16.6 ); QTest::newRow( "clamp(-2,1,5)" ) << "clamp(-2,1,5)" << false << QVariant( 1.0 ); QTest::newRow( "clamp(-2,-10,5)" ) << "clamp(-2,-10,5)" << false << QVariant( -2.0 ); QTest::newRow( "clamp(-2,100,5)" ) << "clamp(-2,100,5)" << false << QVariant( 5.0 ); QTest::newRow( "floor(4.9)" ) << "floor(4.9)" << false << QVariant( 4. ); QTest::newRow( "floor(-4.9)" ) << "floor(-4.9)" << false << QVariant( -5. ); QTest::newRow( "ceil(4.9)" ) << "ceil(4.9)" << false << QVariant( 5. ); @@ -271,6 +274,13 @@ class TestQgsExpression: public QObject QTest::newRow( "scale_linear(-1,0,10,100,200)" ) << "scale_linear(-1,0,10,100,200)" << false << QVariant( 100. ); QTest::newRow( "scale_linear(11,0,10,100,200)" ) << "scale_linear(11,0,10,100,200)" << false << QVariant( 200. ); QTest::newRow( "scale_exp(0.5,0,1,0,1,2)" ) << "scale_exp(0.5,0,1,0,1,2)" << false << QVariant( 0.25 ); QTest::newRow( "scale_exp(0,0,10,100,200,2)" ) << "scale_exp(0,0,10,100,200,2)" << false << QVariant( 100. ); QTest::newRow( "scale_exp(5,0,10,100,200,2)" ) << "scale_exp(5,0,10,100,200,2)" << false << QVariant( 125. ); QTest::newRow( "scale_exp(10,0,10,100,200,0.5)" ) << "scale_exp(10,0,10,100,200,0.5)" << false << QVariant( 200. ); QTest::newRow( "scale_exp(-1,0,10,100,200,0.5)" ) << "scale_exp(-1,0,10,100,200,0.5)" << false << QVariant( 100. ); QTest::newRow( "scale_exp(4,0,9,0,90,0.5)" ) << "scale_exp(4,0,9,0,90,0.5)" << false << QVariant( 60. ); // cast functions QTest::newRow( "double to int" ) << "toint(3.2)" << false << QVariant( 3 ); QTest::newRow( "text to int" ) << "toint('53')" << false << QVariant( 53 );