Package org.geotoolkit.referencing.operation.provider

Providers of transforms and projections implementations.

See: Description

Package org.geotoolkit.referencing.operation.provider Description

Providers of transforms and projections implementations. This package is provided mostly for documentation purpose, since the javadoc of each provider lists the operation names, identifiers (e.g. EPSG codes) and parameters. The preferred way to get a provider is to use the MathTransformFactory class.

Standard parameters
Each provider declares a single ParameterDescriptorGroup constant named PARAMETERS. Each group describes all the parameters expected by an operation method. The set of parameters varies for each projection, but the following can be considered typical:

Each descriptor has many aliases, and those aliases may vary between different projections. For example the false easting parameter is usually called "false_easting" by OGC, while EPSG uses various names like "False easting" or "Easting at false origin".

Dynamic parameters
A few non-standard parameters are defined for compatibility reasons, but delegates their work to standard parameters. Those dynamic parameters are not listed in the parameter values. Dynamic parameters are:

The main purpose of those dynamic parameters is to support some less commonly used conventions without duplicating the most commonly used conventions. The alternative ways are used in NetCDF files for example, which often use spherical models instead than ellipsoidal ones.

Mandatory and optional parameters
Parameters are flagged as either mandatory or optional. A parameter may be mandatory and still have a default value. In the context of this package, "mandatory" means that the parameter is an essential part of the projection defined by standards. Such mandatory parameters will always appears in any Well Known Text (WKT) formatting, even if not explicitly set by the user. For example the central meridian is typically a mandatory parameter with a default value of 0° (the Greenwich meridian).

Optional parameters, on the other hand, are often non-standard extensions. They will appear in WKT formatting only if the user defined explicitly a value which is different than the default value. extensions
Geotk defines a "roll_longitude" boolean parameter. If this parameter is set to TRUE, then any longitude outside the [-180 … 180)° range (upper value is exclusive) will be forced to that range by the addition or subtraction of some multiple of 360°. This applies to both the input of projections and the output of inverse projections.

If this parameter is not provided, then the default behavior is to roll longitudes only if the central meridian is different than zero.

ESRI extensions
In Geotk, axis flips are inferred from the axis orientation. In Well Known Text (WKT), they are given by AXIS elements. But ESRI ignores AXIS elements and uses instead some additional parameters: "X_Scale", "Y_Scale" and "XY_Plane_Rotation". Those parameters are not OGC standards, but are nevertheless provided in Geotk for better inter-operability with ESRI definitions of coordinate reference systems.

Martin Desruisseaux (Geomatys), Rueben Schulz (UBC)
See Also:
Geotk coordinate operations matrix, Projections list on, MathTransformProvider
referencing/geotk-referencing (download)

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