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Differences between ISO/OGC specifications and GeoAPI
Differences between ISO/OGC specifications and GeoAPI
In the following discussion, "specification 2003-73" refers to the
abstract specification Spatial
Referencing by Coordinates (Topic 2), while "specification 2001-009" refers to the
implementation specification Coordinate
Transformation Services. The later was based on a older abstract specification.
- Changes in Metadata
- Changes in Spatial Referencing by Coordinates
- Changes in Feature Geometry
- Changes in Grid Coverage
Changes in Metadata
Addition
Added a new type,
InternationalString
in order to distinguish between localizable and non-localizable character strings.
Not all character string should be localizable; for example Well Know Text
or code name should probably be language neutral. Since the UML doesn't said which
character string are localizable and which one are not, we have done our own guess.
Omission
Omitted the reference system package, since it duplicates
ISO 19111 / OGC Topic 2.
Changes
(None at this time)
Changes in Spatial Referencing by Coordinates
Addition
Factory and operations from the legacy 2001-009 specification have been
ported to the 2003-073 specification. This is because UML diagrams found in the 2003-073
specification contains only attributes or associations, no operations.
Many services found in the legacy 2001-009 specification are not available in latest UML.
More specifically:
- There was nothing like a transformation method taking a point or an array
in argument and returning a transformed point or array (e.g. the legacy
CT_MathTransform
interface).
- There was no factory at all (e.g. the legacy
CT_CoordinateTransformationFactory
interface).
Added a
Projection interface as a special kind of
Conversion. Subinterfaces of
Projection make it possible to check which kind of projection is applied
(planar, cylindrical, conical...).
Added a
Matrix interface.
The legacy 2001-09 specification defined a
PT_Matrix
interface, which is required for derivative computation.
Added the following methods into
AxisDirection:
inverse() and absolute().
Omission
Omitted the IdentifiedObjectBase interface, since the split
between IdentifiedObject and IdentifiedObjectBase in OGC specification
is mostly a workaround for introducing IdentifiedObject in ISO 19111 without changing
ISO 19115, where a base ReferenceSystem is already defined.
Union structures avoided. While it is possible to mimic C's union
in Java, the hacks are usually unconvenient. Furthermore, union are not type-safe even
in C. Consequently, the following structures were omitted:
CD_SecondDefiningParameter (replaced by an API similar to the legacy
CS_Ellipsoid).
Removed the DerivedCRSType code list, since a Java
expression like (baseCRS instanceof FooCRS) provides the same capability
with more flexibility.
Changes
Defined CartesianCS
as a sub-interface of AffineCS.
Allows CompoundCRS
to contains other CompoundCRS. This is a violation of the ISO
CompoundCRS's contract ("A Compound
CRS is a coordinate reference system that combines two or more coordinate reference systems, none
of which can itself be compound"). However, the need for this constraint is not obvious.
Note also that in "Coordinate Transformation Services" (OGC document 01-009), compound CRS was
specified as a pair of arbitrary CRS ("head" and "tail"). Each of them can be an other compound CRS,
allowing the creation of a tree.
Renamed ParameterOperation and related interfaces as
ParameterDescriptor.
Discussion on the mailing list suggested that the previous naming was confusing, since
many developpers expect OperationParameter to contains parameter values,
which is not the case. The ParameterDescriptor name make it more obvious
that this interface contains meta-data about parameters, not the parameter value itself.
Furthermore, it is consistent with naming in usage by the Java Advanced Imaging library.
Renamed ParameterValueGroup.getGroup() method as
getDescriptor()
and moved it in the hierarchy up into
GeneralParameterValue.
The getDescriptor() name was choosen because getGroup() seems too
restrictive, misleading (it returns an abstract definition of a group of parameters, not the
actual group), and for consistency with usage in other Java extensions (e.g. JAI's
ParameterList).
Moved the
GeneralParameterDescriptor,
ParameterDescriptor,
ParameterDescriptorGroup,
GeneralParameterValue,
ParameterValue,
ParameterValueGroup,
InvalidParameterNameException,
InvalidParameterTypeException and
InvalidParameterValueException
interfaces from org.opengis.referencing.operation to org.opengis.parameter.
With this move, GeoAPI has extended the use of these parameter classes to be shared
across several implementations with different needs. This is an accident of implementation
(we produced these parameter classes first. They do happen to be very expressive
and a good candiate for reuse). We also considered:
- ISO 19119 - type specification in terms of ENUM, RANGE and so on. Not enough
information is publically available to proceed.
- Grid Coverage Exchange - parameter description is simple and has been superceeded
by these definitions.
java.beans.ParameterDescriptor -
The Java Beans specification is well known and many tools exist for UI creation
based on this specification.javax.jai.ParameterList -
Java Advanced Imaging contains a ParameterDescriptor infrastructure that has
served as a guideline for how we would like to extend this work.
In the field we are using this set of parameter classes to describe
connection information for WMS, WFS and Database connections - a function that
ISO 19119 - Metadata Services is supposed to fulfill.
Moved up (in the hierarchy) the "maximumOccurs" attribute from
ParameterDescriptorGroup into the
GeneralParameterDescriptor
super-interface, in order to be on per with the "minimumOccurs" attribute.
Changes in Feature Geometry
Addition
(None at this time)
Omission
(None at this time)
Changes
Renamed GM_Object as
Geometry
in order to avoid ambiguity with java.lang.Object.
Moved Envelope
and DirectPosition
in the root geometry package (org.opengis.geometry) since they are
used in many places in most packages.
Changes in Grid Coverage
Addition
In Coverage, added an optional
getRenderableImage
method for interoperability with Java2D.
In SampleDimension, added an optional
getSampleToGeophysics
method as a generalization of scale and offset attributes.
Added
CannotEvaluateException as a super-class of
PointOutsideCoverageException.
Omission
Exceptions
MetadataNameNotFoundException
were declared only once in the CV package, not duplicated in every packages.
Omitted
InvalidIndexException (replaced by IndexOutOfBoundsException) and
ErrorExportingGridCoverageException (replaced by IOException).
Changes
In Coverage, changed
evaluateAsDouble(DirectPosition) into evaluate(DirectPosition, double[])
for reusing optionally pre-allocated array. This is consistent with Java usage in Raster
for example. Same apply to all evaluateAsFoo(DirectPosition) methods.
In GridCoverage, changed
getDataBlockAsDouble(GridRange) into getDataBlock(GridCoverage, double[])
for reusing optionally pre-allocated array. This is consistent with Java usage in Raster
for example. Same apply to all getDataBlockAsFoo(GridRange) methods.
Return type of
Coverage.getSource(int)
was relaxed from GridCoverage to Coverage. Instead, the return
type has been constrained to GridCoverage only in
GridCoverage.getSource(int).
This approach (return type covariance) was already used in "Spatial Referencing by
Coordinates" (ISO 19111). It avoid forward dependency of Coverage toward
GridCoverage and give more flexibility for use of Coverage
with non-gridded data.