Module org.apache.sis.referencing
Class InterpolatedGeocentricTransform
Object
FormattableObject
AbstractMathTransform
DatumShiftTransform
InterpolatedGeocentricTransform
- All Implemented Interfaces:
Serializable
,Parameterized
,LenientComparable
,MathTransform
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:
- Convert input geographic coordinate (λ,φ) to geocentric coordinate (X,Y,Z).
- 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. - Convert the shifted geocentric coordinate (X+ΔX, Y+ΔY, Z+ΔZ) back to a geographic coordinate.
Reference
IGN documentNTG_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:
-
Constructor Summary
ModifierConstructorDescriptionprotected
InterpolatedGeocentricTransform
(Ellipsoid source, boolean isSource3D, Ellipsoid target, boolean isTarget3D, DatumShiftGrid<Angle, Length> grid) Creates a transform from the specified parameters. -
Method Summary
Modifier and TypeMethodDescriptionstatic MathTransform
createGeodeticTransformation
(MathTransformFactory factory, Ellipsoid source, boolean isSource3D, Ellipsoid target, boolean isTarget3D, DatumShiftGrid<Angle, Length> grid) Creates a transformation between two geographic CRS.int
Gets the dimension of input points.int
Gets the dimension of output points.inverse()
Returns the inverse of this interpolated geocentric transform.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, getDomain, 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
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Constructor Details
-
InterpolatedGeocentricTransform
protected InterpolatedGeocentricTransform(Ellipsoid source, boolean isSource3D, Ellipsoid target, boolean isTarget3D, DatumShiftGrid<Angle, Length> grid) Creates a transform from the specified parameters. ThisInterpolatedGeocentricTransform
class expects coordinate values in the following order and units:- longitudes in radians relative to the prime meridian (usually Greenwich),
- latitudes in radians,
- optionally heights above the ellipsoid, in same units than the source ellipsoid axes.
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.
InterpolatedGeocentricTransform
construction, the full conversion chain including the above affine transforms can be created byDatumShiftTransform.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. TheDatumShiftGrid.interpolateInCell(…)
method shall compute (ΔX, ΔY, ΔZ) translations from source to target in the unit of source ellipsoid axes.- See Also:
-
-
Method Details
-
createGeodeticTransformation
public static MathTransform createGeodeticTransformation(MathTransformFactory factory, Ellipsoid source, boolean isSource3D, Ellipsoid target, boolean isTarget3D, DatumShiftGrid<Angle, Length> grid) throws FactoryExceptionCreates a transformation between two geographic CRS. This factory method combines theInterpolatedGeocentricTransform
instance with the steps needed for converting values between degrees to radians. The transform works with input and output coordinates in the following units:- longitudes in degrees relative to the prime meridian (usually Greenwich),
- latitudes in degrees,
- optionally heights above the ellipsoid, in same units than the source ellipsoids axes.
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. TheDatumShiftGrid.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 interfaceMathTransform
- Specified by:
getSourceDimensions
in classAbstractMathTransform
- Returns:
- the input dimension, which is 2 or 3.
- See Also:
-
getTargetDimensions
public int getTargetDimensions()Gets the dimension of output points.- Specified by:
getTargetDimensions
in interfaceMathTransform
- Specified by:
getTargetDimensions
in classAbstractMathTransform
- Returns:
- the output dimension, which is 2 or 3.
- See Also:
-
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 classAbstractMathTransform
- Parameters:
srcPts
- the array containing the source coordinates (cannot benull
).srcOff
- the offset to the point to be transformed in the source array.dstPts
- the array into which the transformed coordinates is returned. May be the same thansrcPts
. May benull
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, orfalse
if not needed.- Returns:
- the matrix of the transform derivative at the given source position,
or
null
if thederivate
argument isfalse
. - Throws:
TransformException
- if the point cannot be transformed or if a problem occurred while calculating the derivative.- See Also:
-
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 interfaceMathTransform
- Overrides:
inverse
in classAbstractMathTransform
- Returns:
- a transform from the target ellipsoid to the source ellipsoid of this transform.
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