org.geotools.feature.visitor

Class StandardDeviationVisitor

Object

StandardDeviationVisitor

All Implemented Interfaces:

FeatureAttributeVisitor, FeatureCalc, FeatureVisitor

public class StandardDeviationVisitor
extends Object
implements FeatureCalc, FeatureAttributeVisitor

Determines the standard deviation.

            ----------------------------
            |  1   ---
 Std dev =  | ___  \   ( x - mean ) ^ 2
           \|  N   /__
 

aka std dev = sqrt((sum((x-mean)^2))/N) where N is the number of samples.

It uses the rolling variance algorithm described here: http://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#On-line_algorithm

Author:

Cory Horner, Refractions Research Inc., Andrea Aime, GeoSolutions

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	StandardDeviationVisitor.Result

Constructor Summary

Constructors

Constructor and Description
StandardDeviationVisitor(Expression expr) Constructs a standard deviation visitor based on the specified expression
StandardDeviationVisitor(Expression expr, double average) Deprecated. use StandardDeviationVisitor(Expression) insteads

Method Summary

Modifier and Type	Method and Description
List<Expression>	getExpressions() List of expressions used by visitor.
double	getMean() mean value generated when calcualting standard deviation
int	getNaNCount()
int	getNullCount()
CalcResult	getResult() Returns the result of the calculation as a handy object which can be merged and modified.
void	init(SimpleFeatureCollection collection)
void	reset()
void	visit(Feature feature) Visit the provided feature.
void	visit(SimpleFeature feature)

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

StandardDeviationVisitor

@Deprecated
public StandardDeviationVisitor(Expression expr,
                                            double average)

Deprecated. use StandardDeviationVisitor(Expression) insteads

Constructor left for backwards compatibility. The current algorithm uses a on line computation that does not require the average to be calculated in advance

Parameters:

expr -

average -

StandardDeviationVisitor

public StandardDeviationVisitor(Expression expr)

Constructs a standard deviation visitor based on the specified expression

Parameters:

expr -

average -

Method Detail

init

public void init(SimpleFeatureCollection collection)

getExpressions

public List<Expression> getExpressions()

Description copied from interface: FeatureAttributeVisitor

List of expressions used by visitor.

Specified by:

getExpressions in interface FeatureAttributeVisitor

getResult

public CalcResult getResult()

Description copied from interface: FeatureCalc

Returns the result of the calculation as a handy object which can be merged and modified.

Specified by:

getResult in interface FeatureCalc

Returns:

the results of the calculation

visit

public void visit(SimpleFeature feature)

visit

public void visit(Feature feature)

Description copied from interface: FeatureVisitor

Visit the provided feature.

Please consult the documentation for the FeatureCollection you are visiting to learn more - the provided feature may be invalid, or read only.

Specified by:

visit in interface FeatureVisitor

reset

public void reset()

getMean

public double getMean()

mean value generated when calcualting standard deviation

getNaNCount

public int getNaNCount()

Returns:

the number of features which returned a NaN

getNullCount

public int getNullCount()

Returns:

the number of features which returned a null