- Direct Known Subclasses:
There is many different datum shift methods, ranging from transformations as simple as adding a constant offset
to geographic coordinates, to more complex transformations involving conversions to geocentric coordinates and/or
interpolations in a datum shift grid. The simple cases like adding a constant offset
are handled by other
MathTransform implementations like
More complex methods are subclasses of this
DatumShiftTransform base class, but users should not assume
that this is the case of every transforms performing a datum shift.
Datum shift methods overviewThe two CRS's ellipsoids have slightly different scale and rotation in space, and their center are located in a slightly different position. Consequently geodetic datum shifts are often approximated by a constant scale, rotation and translation applied on geocentric coordinates. Those approximations are handled in SIS by concatenations of
LinearTransforminstead of a specific
If the geodetic datum shifts is approximated only by a geocentric translation without any scale or rotation,
and if an error of a few centimetres it acceptable, then the
MolodenskyTransform subclass can be used
as an approximation of the above method. The Molodensky method requires less floating point operations since
it applies directly on geographic coordinates, without conversions to geocentric coordinates.
Some countries go one step further and allow the above geocentric translations to be non-constant.
Instead, a different geocentric translation is interpolated for each geographic input coordinates.
This case is handled by the
InterpolatedGeocentricTransform subclass, or its
InterpolatedMolodenskyTransform variant if a few centimetres accuracy lost can be afforded.
A simpler alternative to the above is to interpolate translations to apply directly on geographic coordinates.
This is the approach taken by NADCON and NTv2 grids.
SIS handles those datum shifts with the
Nested Class Summary
Method SummaryModifier and TypeMethodDescription
protected intComputes a hash value for this transform.
booleanCompares the specified object with this math transform for equality.
protected ContextualParametersReturns the parameters used for creating the complete transformation.Returns the internal parameter values of this
DatumShiftTransforminstance (ignoring context).
Methods inherited from class AbstractMathTransform
derivative, equals, formatTo, getParameterDescriptors, getSourceDimensions, getTargetDimensions, hashCode, inverse, isIdentity, transform, transform, transform, transform, transform, transform, tryConcatenate
Methods inherited from class Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
getParameterValuesReturns the internal parameter values of this
DatumShiftTransforminstance (ignoring context). The parameters returned by this method do not necessarily describe the whole datum shift process, because
DatumShiftTransforminstances are often preceeded and followed by linear conversions. It may be conversions between degrees and radians units, or conversions from geodetic coordinates to grid indices.Example: The chain of transforms of anThis method returns the parameters for the part in the middle of above example. The content of this part is highly implementation-dependent and used mostly for debugging purposes. The parameters that describe the process as a whole are rather given by
- Geographic to geocentric conversion
- Geocentric interpolation
- Geocentric to geographic conversion
getContextualParametersprotected ContextualParameters getContextualParameters()Returns the parameters used for creating the complete transformation. Those parameters describe a sequence of normalize →
this→ denormalize transforms, not including axis swapping. Those parameters are used for formatting Well Known Text (WKT) and error messages.
computeHashCodeprotected int computeHashCode()Computes a hash value for this transform. This method is invoked by
AbstractMathTransform.hashCode()when first needed.
equalsCompares the specified object with this math transform for equality.
- Specified by:
object- the object to compare with this transform.
mode- the strictness level of the comparison. Default to
trueif the given object is considered equals to this math transform.
- See Also: