Package org.apache.sis.referencing.operation.transform

Class ContextualParameters

java.lang.Object

org.apache.sis.parameter.Parameters

org.apache.sis.referencing.operation.transform.ContextualParameters

All Implemented Interfaces:

Serializable, Cloneable, org.opengis.parameter.GeneralParameterValue, org.opengis.parameter.ParameterValueGroup

public class ContextualParameters
extends Parameters
implements Serializable

The parameters that describe a sequence of normalize → non-linear kernel → denormalize transforms as a whole. The normalize and denormalize steps must be affine transforms, while the non-linear kernel is arbitrary.

Note: actually there is nothing in this class which force the kernel to be non-linear. But this class is useless if the kernel is linear, because 3 linear steps can be efficiently concatenated in a single affine transform.

Contextual parameters can be associated to the non-linear kernel step of the above-cited sequence. Since the parameter values of the non-linear kernel contains only normalized parameters (e.g. a map projection on an ellipsoid having a semi-major axis length of 1), Apache SIS needs contextual information for reconstructing the parameters of the complete transforms chain.

Usage in map projections

This object is used mostly for Apache SIS implementation of map projections, where the non-linear kernel is a normalized projection. The complete map projection (ignoring changes of axis order) is a chain of 3 transforms as shown below:

→

Map projection on a normalized ellipsoid

→

ContextualParameters is typically created and used as below:

1. A MathTransformProvider instantiates a class from the map projection package. Note that different providers may instantiate the same map projection class. For example, both "Mercator (variant A)" and "Mercator (variant B)" methods instantiate the same Mercator class, but with different ways to represent the parameters.
2. The map projection constructor fetches all parameters that it needs from the user supplied Parameters, initializes the projection, then saves the parameter values that it actually used in a new ContextualParameters instance.
3. The map projection constructor may keep only the non-linear parameters for itself, and gives the linear parameters to the normalizeGeographicInputs(…) and MatrixSIS.convertAfter(…) methods, which will create the matrices show above. The projection constructor is free to apply additional operations on the two affine transforms (normalize / denormalize) before or after the above-cited methods have been invoked.
4. After all parameter values have been set and the normalize / denormalize matrices defined, the completeTransform(…) method will mark this ContextualParameters object as unmodifiable and create the chain of transforms from (λ,φ) in angular degrees to (x,y) in metres. Note that conversions to other units and changes in axis order are not the purpose of this transforms chain – they are separated steps.

Serialization

Serialized instances of this class are not guaranteed to be compatible with future SIS versions. Serialization should be used only for short term storage or RMI between applications running the same SIS version.

Since:

0.6

Version:

1.3

Author:

Martin Desruisseaux (Geomatys)

See Also:

• NormalizedProjection
• AbstractMathTransform.getContextualParameters()
• Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static enum	ContextualParameters.MatrixRole	Whether a matrix is used for normalization or denormalization before or after a non-linear operation.

Constructor Summary

Constructors

Constructor	Description
ContextualParameters(org.opengis.parameter.ParameterDescriptorGroup descriptor, int srcDim, int tgtDim)	Creates a new group of parameters with the given descriptor.

Method Summary

Modifier and Type	Method	Description
org.opengis.parameter.ParameterValueGroup	addGroup(String name)	Unsupported operation, since ContextualParameters groups do not contain sub-groups.
ContextualParameters	clone()	Returns a modifiable clone of this parameter value group.
org.opengis.referencing.operation.MathTransform	completeTransform(org.opengis.referencing.operation.MathTransformFactory factory, org.opengis.referencing.operation.MathTransform kernel)	Marks this ContextualParameter as unmodifiable and creates the normalize → kernel → denormalize transforms chain.
MatrixSIS	denormalizeGeographicOutputs(double λ0)	Appends a denormalization step after the non-linear kernel, which will convert input coordinates in the two first dimensions from radians to degrees.
boolean	equals(Object object)	Compares the given object with the parameters for equality.
final org.opengis.parameter.ParameterDescriptorGroup	getDescriptor()	Returns the parameters for the normalize → non-linear kernel → denormalize sequence as a whole.
final MatrixSIS	getMatrix(ContextualParameters.MatrixRole role)	Returns the affine transforms to be applied before or after the non-linear kernel operation.
List<org.opengis.parameter.ParameterValueGroup>	groups(String name)	Unsupported operation, since ContextualParameters groups do not contain sub-groups.
int	hashCode()	Returns a hash code value for this object.
MatrixSIS	normalizeGeographicInputs(double λ0)	Prepends a normalization step converting input coordinates in the two first dimensions from degrees to radians.
org.opengis.parameter.ParameterValue<?>	parameter(String name)	Returns the parameter value of the given name.
List<org.opengis.parameter.GeneralParameterValue>	values()	Returns an unmodifiable list containing all parameters in this group.

Methods inherited from class org.apache.sis.parameter.Parameters

booleanValue, cast, cast, castOrWrap, copy, doubleValue, doubleValue, doubleValueList, getDescriptors, getMandatoryValue, getMemberName, getOrCreate, getValue, getValueDomain, intValue, intValueList, isUnmodifiable, print, stringValue, toString, unmodifiable, unmodifiable

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Details

ContextualParameters

public ContextualParameters(org.opengis.parameter.ParameterDescriptorGroup descriptor,
 int srcDim,
 int tgtDim)

Creates a new group of parameters with the given descriptor. The method parameters shall describe the normalize → non-linear kernel → denormalize sequence as a whole. After construction, callers shall:

• Set the relevant parameter values by calls to parameter(…).setValue(…).
• Modify the element values in normalization / denormalization affine transforms, optionally by calls to the convenience methods in this class.
• Get the complete transforms chain with a call completeTransform(…)

See class javadoc for more information.

Parameters:

descriptor - the parameter descriptor.

srcDim - number of source dimensions.

tgtDim - number of target dimensions.

Since:

1.0

Method Details

getDescriptor

public final org.opengis.parameter.ParameterDescriptorGroup getDescriptor()

Returns the parameters for the normalize → non-linear kernel → denormalize sequence as a whole. This is the parameter descriptor of the operation method given to the constructor.

The values for those parameters is given by the values() method. Those values may be used in the normalization / denormalization transforms, in the kernel, or both.

Note: The definition of "kernel" is left to implementers. In the particular case of Apache SIS implementation of map projections, kernels are instances of NormalizedProjection. Other "kernels" in SIS are EllipsoidToCentricTransform and MolodenskyTransform.

Specified by:

getDescriptor in interface org.opengis.parameter.GeneralParameterValue

Specified by:

getDescriptor in interface org.opengis.parameter.ParameterValueGroup

Returns:

the description of the parameters.

getMatrix

public final MatrixSIS getMatrix(ContextualParameters.MatrixRole role)

Returns the affine transforms to be applied before or after the non-linear kernel operation. Immediately after construction, those matrices are modifiable identity matrices. Callers can modify the matrix element values, typically by calls to the MatrixSIS.convertBefore(…) method. Alternatively, the following methods can be invoked for applying some frequently used configurations:

• normalizeGeographicInputs(double)
• denormalizeGeographicOutputs(double)

After the completeTransform(…) method has been invoked, the matrices returned by this method are unmodifiable.

Application to map projections: after NormalizedProjection construction, the matrices returned by projection.getContextualParameters().getMatrix(…) are initialized to the values shown below. Note that some NormalizedProjection subclasses apply further modifications to those matrices.

Initial matrix coefficients after NormalizedProjection construction

getMatrix(NORMALIZATION)	getMatrix(DENORMALIZATION)

Parameters:

role - NORMALIZATION for fetching the normalization transform to apply before the kernel, DENORMALIZATION for the denormalization transform to apply after the kernel, or INVERSE_* for the inverse of the above-cited matrices.

Returns:

the matrix for the requested normalization or denormalization affine transform.

Since:

0.7

normalizeGeographicInputs

public MatrixSIS normalizeGeographicInputs(double λ0)

Prepends a normalization step converting input coordinates in the two first dimensions from degrees to radians. The normalization can optionally subtract the given λ₀ value (in degrees) from the longitude.

Invoking this method is equivalent to concatenating the normalization matrix with the following matrix. This will have the effect of applying the conversion described above before any other operation:

Parameters:

λ0 - longitude of the central meridian, in degrees.

Returns:

the normalization affine transform as a matrix. Callers can change that matrix directly if they want to apply additional normalization operations.

Throws:

IllegalStateException - if this ContextualParameter has been made unmodifiable.

denormalizeGeographicOutputs

public MatrixSIS denormalizeGeographicOutputs(double λ0)

Appends a denormalization step after the non-linear kernel, which will convert input coordinates in the two first dimensions from radians to degrees. After this conversion, the denormalization can optionally add the given λ₀ value (in degrees) to the longitude.

Invoking this method is equivalent to concatenating the denormalization matrix with the following matrix. This will have the effect of applying the conversion described above after the non-linear kernel operation:

Parameters:

λ0 - longitude of the central meridian, in degrees.

Returns:

the denormalization affine transform as a matrix. Callers can change that matrix directly if they want to apply additional denormalization operations.

Throws:

IllegalStateException - if this ContextualParameter has been made unmodifiable.

completeTransform

public org.opengis.referencing.operation.MathTransform completeTransform(org.opengis.referencing.operation.MathTransformFactory factory,
 org.opengis.referencing.operation.MathTransform kernel)
                                                                  throws org.opengis.util.FactoryException

Marks this ContextualParameter as unmodifiable and creates the normalize → kernel → denormalize transforms chain. This method shall be invoked only after the (de)normalization matrices have been set to their final values.

The transforms chain created by this method does not include any step for changing axis order or for converting to units other than degrees or metres. Such steps, if desired, should be defined outside ContextualParameters. Efficient concatenation of those steps will happen "under the hood".

Parameters:

factory - the factory to use for creating math transform instances.

kernel - the (usually non-linear) kernel. This is often a NormalizedProjection.

Returns:

the concatenation of normalize → the given kernel → denormalize transforms.

Throws:

org.opengis.util.FactoryException - if an error occurred while creating a math transform instance.

See Also:

• NormalizedProjection.createMapProjection(MathTransformFactory)

parameter

public org.opengis.parameter.ParameterValue<?> parameter(String name)
                                                  throws org.opengis.parameter.ParameterNotFoundException

Returns the parameter value of the given name. Before the call to completeTransform(…), this method can be used for setting parameter values like below: After the call to completeTransform(…), the returned parameters are read-only.

Specified by:

parameter in interface org.opengis.parameter.ParameterValueGroup

Parameters:

name - the name of the parameter to search.

Returns:

the parameter value for the given name.

Throws:

org.opengis.parameter.ParameterNotFoundException - if there is no parameter of the given name.

values

public List<org.opengis.parameter.GeneralParameterValue> values()

Returns an unmodifiable list containing all parameters in this group. Callers should not attempt to modify the parameter values in this list.

Specified by:

values in interface org.opengis.parameter.ParameterValueGroup

Returns:

all parameter values.

groups

public List<org.opengis.parameter.ParameterValueGroup> groups(String name)

Unsupported operation, since ContextualParameters groups do not contain sub-groups.

Specified by:

groups in interface org.opengis.parameter.ParameterValueGroup

Parameters:

name - ignored.

Returns:

never returned.

addGroup

public org.opengis.parameter.ParameterValueGroup addGroup(String name)

Unsupported operation, since ContextualParameters groups do not contain sub-groups.

Specified by:

addGroup in interface org.opengis.parameter.ParameterValueGroup

Parameters:

name - ignored.

Returns:

never returned.

clone

public ContextualParameters clone()

Returns a modifiable clone of this parameter value group.

Specified by:

clone in interface org.opengis.parameter.GeneralParameterValue

Specified by:

clone in interface org.opengis.parameter.ParameterValueGroup

Overrides:

clone in class Parameters

Returns:

a clone of this parameter value group.

See Also:

• Parameters.copy(ParameterValueGroup, ParameterValueGroup)

hashCode

public int hashCode()

Returns a hash code value for this object. This value is implementation-dependent and may change in any future version.

Overrides:

hashCode in class Object

equals

public boolean equals(Object object)

Compares the given object with the parameters for equality.

Overrides:

equals in class Object

Parameters:

object - the object to compare with the parameters.

Returns:

true if the given object is equal to this one.