org.apache.sis.referencing.operation.transform

Class InterpolatedGeocentricTransform

Object

FormattableObject

AbstractMathTransform

DatumShiftTransform

InterpolatedGeocentricTransform

All Implemented Interfaces:

Serializable, Parameterized, LenientComparable, MathTransform

public class InterpolatedGeocentricTransform
extends DatumShiftTransform

Transforms between two geographic CRS by performing geocentric translations interpolated from a grid file. This transform is used mainly for "France geocentric interpolation" (ESPG:9655) datum shifts, but Apache SIS implementation allows the use for other regions.

Algorithm

This class transforms two- or three- dimensional coordinates from a geographic CRS to another geographic CRS. The changes between source and target coordinates are small (usually less than 400 metres), but vary for every position. Those changes are provided in a datum shift grid, usually loaded from one or two files.

Many datum shift grids like NADCON and NTv2 apply the changes directly on geographic coordinates. This relatively simple case is handled by Interpolated­Transform. But the Interpolated­Geocentric­Transform algorithm uses the grid in a more complex way:

1. Convert input geographic coordinate (λ,φ) to geocentric coordinate (X,Y,Z).
2. Ask Datum­Shift­Grid for the offset to apply for coordinate (λ,φ). But instead of returning a (Δλ, Δφ) offset, the grid shall return a (ΔX, ΔY, ΔZ) offset.
3. Convert the shifted geocentric coordinate (X+ΔX, Y+ΔY, Z+ΔZ) back to a geographic coordinate.

Source: IGN document NTG_88.pdf, "Grille de paramètres de transformation de coordonnées" at http://www.ign.fr. Note however that the signs of (ΔX, ΔY, ΔZ) values expected by this class are the opposite of the signs used in NTG_88 document. This is because NTG_88 grid defines shifts from target to source, while this class expects shifts from source to target.

Note: this algorithm is not the same as a (theoretical) Ellipsoid­To­Centric­Transform → Interpolated­Transform → (inverse of Ellipsoid­To­Centric­Transform) concatenation because the Datum­Shift­Grid inputs are geographic coordinates even if the interpolated grid values are in geocentric space.

Performance consideration

Interpolated­Molodensky­Transform performs the same calculation more efficiently at the cost of a few centimetres error. Both classes are instantiated in the same way and expect the same inputs.

Since:

0.7

See Also:

Interpolated­Molodensky­Transform, Serialized Form

Defined in the sis-referencing module

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	InterpolatedGeocentricTransform(Ellipsoid source, boolean isSource3D, Ellipsoid target, boolean isTarget3D, DatumShiftGrid<Angle,Length> grid) Creates a transform from the specified parameters.

Method Summary

Modifier and Type	Method and Description
static MathTransform	createGeodeticTransformation(MathTransformFactory factory, Ellipsoid source, boolean isSource3D, Ellipsoid target, boolean isTarget3D, DatumShiftGrid<Angle,Length> grid) Creates a transformation between two geographic CRS.
int	getSourceDimensions() Gets the dimension of input points.
int	getTargetDimensions() Gets the dimension of output points.
MathTransform	inverse() Returns the inverse of this interpolated geocentric transform.
Matrix	transform(double[] srcPts, int srcOff, double[] dstPts, int dstOff, boolean derivate) Transforms the (λ,φ) or (λ,φ,h) coordinates between two geographic CRS, and optionally returns the derivative at that location.

Methods inherited from class DatumShiftTransform

compute­Hash­Code, equals, get­Contextual­Parameters, get­Parameter­Values

Methods inherited from class AbstractMathTransform

derivative, equals, format­To, get­Parameter­Descriptors, hash­Code, is­Identity, transform, transform, transform, transform, transform, try­Concatenate

Methods inherited from class FormattableObject

print, to­String, to­String, to­WKT

Methods inherited from class Object

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

Methods inherited from interface MathTransform

to­WKT

Constructor Detail

InterpolatedGeocentricTransform

protected InterpolatedGeocentricTransform(Ellipsoid source,
                                          boolean isSource3D,
                                          Ellipsoid target,
                                          boolean isTarget3D,
                                          DatumShiftGrid<Angle,Length> grid)

Creates a transform from the specified parameters. This Interpolated­Geocentric­Transform class expects ordinate values in the following order and units:

1. longitudes in radians relative to the prime meridian (usually Greenwich),
2. latitudes in radians,
3. optionally heights above the ellipsoid, in same units than the source ellipsoid axes.

For converting geographic coordinates in degrees, Interpolated­Geocentric­Transform instances need to be concatenated with the following affine transforms:

• Normalization before Interpolated­Geocentric­Transform:
  • Conversion of (λ,φ) from degrees to radians.
• Denormalization after Interpolated­Geocentric­Transform:
  • Conversion of (λ,φ) from radians to degrees.

After Interpolated­Geocentric­Transform construction, the full conversion chain including the above affine transforms can be created by Datum­Shift­Transform.get­Contextual­Parameters().complete­Transform(factory, this)}.

Parameters:

source - the source ellipsoid.

is­Source3D - true if the source coordinates have a height.

target - the target ellipsoid.

is­Target3D - true if the target coordinates have a height.

grid - the grid of datum shifts from source to target datum. The Datum­Shift­Grid.interpolate­In­Cell(…) method shall compute (ΔX, ΔY, ΔZ) translations from source to target in the unit of source ellipsoid axes.

See Also:

create­Geodetic­Transformation(Math­Transform­Factory, Ellipsoid, boolean, Ellipsoid, boolean, Datum­Shift­Grid)

Method Detail

createGeodeticTransformation

public static MathTransform createGeodeticTransformation(MathTransformFactory factory,
                                                         Ellipsoid source,
                                                         boolean isSource3D,
                                                         Ellipsoid target,
                                                         boolean isTarget3D,
                                                         DatumShiftGrid<Angle,Length> grid)
                                                  throws FactoryException

Creates a transformation between two geographic CRS. This factory method combines the Interpolated­Geocentric­Transform instance with the steps needed for converting values between degrees to radians. The transform works with input and output coordinates in the following units:

1. longitudes in degrees relative to the prime meridian (usually Greenwich),
2. latitudes in degrees,
3. optionally heights above the ellipsoid, in same units than the source ellipsoids axes.

Note however that the given grid instance shall expect geographic coordinates (λ,φ) in radians.

Parameters:

factory - the factory to use for creating the transform.

source - the source ellipsoid.

is­Source3D - true if the source coordinates have a height.

target - the target ellipsoid.

is­Target3D - true if the target coordinates have a height.

grid - the grid of datum shifts from source to target datum. The Datum­Shift­Grid.interpolate­In­Cell(…) method shall compute (ΔX, ΔY, ΔZ) translations from source to target in the unit of source ellipsoid axes.

Returns:

the transformation between geographic coordinates in degrees.

Throws:

Factory­Exception - if an error occurred while creating a transform.

getSourceDimensions

public int getSourceDimensions()

Gets the dimension of input points.

Specified by:

get­Source­Dimensions in interface Math­Transform

Specified by:

get­Source­Dimensions in class Abstract­Math­Transform

Returns:

the input dimension, which is 2 or 3.

See Also:

Default­Operation­Method.get­Source­Dimensions()

getTargetDimensions

public int getTargetDimensions()

Gets the dimension of output points.

Specified by:

get­Target­Dimensions in interface Math­Transform

Specified by:

get­Target­Dimensions in class Abstract­Math­Transform

Returns:

the output dimension, which is 2 or 3.

See Also:

Default­Operation­Method.get­Target­Dimensions()

transform

public Matrix transform(double[] srcPts,
                        int srcOff,
                        double[] dstPts,
                        int dstOff,
                        boolean derivate)
                 throws TransformException

Transforms the (λ,φ) or (λ,φ,h) coordinates between two geographic CRS, and optionally returns the derivative at that location.

Specified by:

transform in class Abstract­Math­Transform

Parameters:

src­Pts - the array containing the source coordinate (can not be null).

src­Off - the offset to the point to be transformed in the source array.

dst­Pts - the array into which the transformed coordinate is returned. May be the same than src­Pts. May be null if only the derivative matrix is desired.

dst­Off - the offset to the location of the transformed point that is stored in the destination array.

derivate - true for computing the derivative, or false if not needed.

Returns:

the matrix of the transform derivative at the given source position, or null if the derivate argument is false.

Throws:

Transform­Exception - if the point can not be transformed or if a problem occurred while calculating the derivative.

See Also:

Abstract­Math­Transform.derivative(Direct­Position), Abstract­Math­Transform.transform(Direct­Position, Direct­Position), Math­Transforms.derivative­And­Transform(Math­Transform, double[], int, double[], int)

inverse

public MathTransform inverse()

Returns the inverse of this interpolated geocentric transform. The source ellipsoid of the returned transform will be the target ellipsoid of this transform, and conversely.

Specified by:

inverse in interface Math­Transform

Overrides:

inverse in class Abstract­Math­Transform

Returns:

a transform from the target ellipsoid to the source ellipsoid of this transform.