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

Class InterpolatedGeocentricTransform

java.lang.Object
org.apache.sis.io.wkt.FormattableObject
org.apache.sis.referencing.operation.transform.AbstractMathTransform
org.apache.sis.referencing.operation.transform.DatumShiftTransform
org.apache.sis.referencing.operation.transform.InterpolatedGeocentricTransform
All Implemented Interfaces:
Serializable, Parameterized, LenientComparable, org.opengis.referencing.operation.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
Version:
1.0
Author:
Simon Reynard (Geomatys), Martin Desruisseaux (Geomatys)
See Also:

  • Constructor Details

    • InterpolatedGeocentricTransform

      protected InterpolatedGeocentricTransform(org.opengis.referencing.datum.Ellipsoid source, boolean isSource3D, org.opengis.referencing.datum.Ellipsoid target, boolean isTarget3D, DatumShiftGrid<javax.measure.quantity.Angle,javax.measure.quantity.Length> grid)
      Creates a transform from the specified parameters. This InterpolatedGeocentricTransform class expects coordinate 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:

  • Method Details

    • createGeodeticTransformation

      public static org.opengis.referencing.operation.MathTransform createGeodeticTransformation(org.opengis.referencing.operation.MathTransformFactory factory, org.opengis.referencing.datum.Ellipsoid source, boolean isSource3D, org.opengis.referencing.datum.Ellipsoid target, boolean isTarget3D, DatumShiftGrid<javax.measure.quantity.Angle,javax.measure.quantity.Length> grid) throws org.opengis.util.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:
      org.opengis.util.FactoryException - if an error occurred while creating a transform.

    • getSourceDimensions

      public int getSourceDimensions()
      Gets the dimension of input points.
      Specified by:
      getSourceDimensions in interface org.opengis.referencing.operation.MathTransform
      Specified by:
      getSourceDimensions in class AbstractMathTransform
      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 interface org.opengis.referencing.operation.MathTransform
      Specified by:
      getTargetDimensions in class AbstractMathTransform
      Returns:
      the output dimension, which is 2 or 3.
      See Also:

    • transform

      public org.opengis.referencing.operation.Matrix transform(double[] srcPts, int srcOff, double[] dstPts, int dstOff, boolean derivate) throws org.opengis.referencing.operation.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 coordinates (cannot be null).
      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 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:
      org.opengis.referencing.operation.TransformException - if the point cannot be transformed or if a problem occurred while calculating the derivative.
      See Also:

    • inverse

      public org.opengis.referencing.operation.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 org.opengis.referencing.operation.MathTransform
      Overrides:
      inverse in class AbstractMathTransform
      Returns:
      a transform from the target ellipsoid to the source ellipsoid of this transform.