Class InterpolateFunction

  • All Implemented Interfaces:
    Expression, Function

    public class InterpolateFunction
    extends Object
    implements Function
    This is an implemenation of the Interpolate function as defined by OGC Symbology Encoding (SE) 1.1 specification.

    The first parameter should be either the name of a numeric feature property or, if this function is being used as a raster colormap, the String "RasterData" (case-insensitive).

    Following this there should be a sequence of interpolation points, each of which is described by two parameters: the first a datum and the second a return value. In the SE speicification these parameters are expected to be Literals but in this implementation more general Expressions are also supported.

    Two optional parameters can be provided following the interpolation points: A "method" parameter which can take the values "numeric" or "color" and a "mode" parameter which can take the values "linear", "cosine" or "cubic" (Note: it would make more sense if these terms were reversed but we are adhering to their use as published in the OGC specification).

    Number of points and interpolation modes

    • Linear and cosine interpolation each require at least two interpolation points to be supplied.
    • Cubic interpolation normally requires at least four points with at least two points either side of the value being interpolated. In this function, deal generously with values that lie in the first or last interpolation segment by adding a duplicate of the first or last point as an extra point. This means that it is allowed (though not necessarily sensible) to use cubic interpolation with only three points.
    • If only two points are supplied but cubic interpolation is specified, the function will fall back to linear interpolation.
    • For all interpolation modes, incoming values outside the range of the interpolation points will be mapped to the value of the closest point (min or max).
    • The function will accept a single interpolation point, but all incoming values will simply be mapped to the value of that point regardless of the type of interpolation requested.
    • If no interpolation points are supplied, an Exception is thrown.
    Michael Bedward, Johann Sorel (Geomatys)
    • Field Detail


        public static final String MODE_LINEAR
        Use as a literal value to indicate interpolation mode
        See Also:
        Constant Field Values

        public static final String MODE_COSINE
        Use as a literal value to indicate interpolation mode
        See Also:
        Constant Field Values
      • MODE_CUBIC

        public static final String MODE_CUBIC
        Use as a literal value to indicate interpolation mode
        See Also:
        Constant Field Values

        public static final String METHOD_NUMERIC
        Use as a literal value to indicate interpolation method
        See Also:
        Constant Field Values

        public static final String METHOD_COLOR
        Use as a literal value to indicate interpolation method
        See Also:
        Constant Field Values

        public static final String RASTER_DATA
        Use as a PropertyName when defining a color map. The "Raterdata" is expected to apply to only a single band;
        See Also:
        Constant Field Values
      • NAME

        public static final FunctionName NAME
        Make the instance of FunctionName available in a consistent spot.
    • Constructor Detail

      • InterpolateFunction

        public InterpolateFunction()
    • Method Detail

      • getName

        public String getName()
        Description copied from interface: Function
        Returns the name of the function to be called. For example, this might be "cos" or "atan2".

        You can use this name to look up the number of required parameters in a FilterCapabilities data structure. For the specific meaning of the required parameters you will need to consult the documentation.

        Specified by:
        getName in interface Function
      • getFunctionName

        public FunctionName getFunctionName()
        Description copied from interface: Function
        Access to the FunctionName description as used in a FilterCapabilities document.
        Specified by:
        getFunctionName in interface Function
        FunctionName description, if available.
      • getParameters

        public List<Expression> getParameters()
        Description copied from interface: Function
        Returns the list subexpressions that will be evaluated to provide the parameters to the function.
        Specified by:
        getParameters in interface Function
      • accept

        public Object accept​(ExpressionVisitor visitor,
                             Object extraData)
        Description copied from interface: Expression
        Accepts a visitor. Subclasses must implement with a method whose content is the following:
        return visitor.visit(this, extraData);
        Specified by:
        accept in interface Expression
      • evaluate

        public Object evaluate​(Object object)
        Description copied from interface: Expression
        Evaluates the given expression based on the content of the given object.
        Specified by:
        evaluate in interface Expression
        computed value
      • evaluate

        public <T> T evaluate​(Object object,
                              Class<T> context)
        Evaluates the given expressoin based on the content of the given object and the context type.

        The context parameter is used to control the type of the result of the expression. A particular expression may not be able to evaluate to an instance of context. Therefore to be safe calling code should do a null check on the return value of this method, and call Expression.evaluate(Object) if neccessary. Example:

          Object input = ...;
          String result = expression.evaluate( input, String.class );
          if ( result == null ) {
             result = expression.evalute( input ).toString();

        Implementations that can not return a result as an instance of context should return null.

        When context is unspecified (i.e. null or Object.class), it'll be derived from the method parameter, as java.awt.Color.class when method == COLOR, and as java.lang.Double when method == NUMERIC.

        Specified by:
        evaluate in interface Expression
        Type Parameters:
        T - The type of the returned object.
        object - The object to evaluate the expression against.
        context - The type of the resulting value of the expression.
        Evaluates the given expression based on the content of the given object an an instance of context.
        IllegalArgumentException - if context == java.awt.Color.class and method != COLOR
      • getFallbackValue

        public Literal getFallbackValue()
        Description copied from interface: Function
        The value of the fallbackValue attribute is used as a default value, if the SE implementation does not support the function. If the implementation supports the function, then the result value is determined by executing the function.
        Specified by:
        getFallbackValue in interface Function
        Optional literal to use if an implementation for this function is not available.
      • toString

        public String toString()
        Creates a String representation of this Function with the function name and the arguments.
        toString in class Object
      • hashCode

        public int hashCode()
        hashCode in class Object