The following is a list of the projection parameters used in the Geotools referencing module. These try to follow the OGC Coordinate Transformation Services specification (OGC 01-009), but this document only specified the parameters for a few projections. When in doubt we have followed the EPSG Guidance Note Number 7 and suggestions from the Projections Transform List.
Parameters can have more than one name, and are recognised by all the names known to the MathTransformFactory. Many classification and parameter names in GeoTools come from the legacy OGC 01-009 document. But what about other standards for classification names (e.g., “Transverse_Mercator” and “Orthogonal”) and parameter names (e.g., “semi_major”)?
GeoTIFF parameter names
In addition to OGC 01-009, we used an other source of very valuable references for classification and parameter names: the GeoTIFF projection list:
This list provides both GeoTIFF and OGC classification and parameter names. This web site was actually one of our main sources for classification and parameter names in Geotools. The “Mercator (1SP)” projection in this list provides the “latitude_of_origin” and similar parameters.
Custom parameter names
But let’s say I’m a developer and I want to develop something that has no “official” names for the parameters? If we can’t find a standard name, we use ours own. This is the case for example of the “Logarithmic” transform.
Authorities for Parameter and Classification Names
However, each name is always associated to an authority (or a “scope” in the context of scoped names). Thats said, the full name of “semi_major” is actually “OGC:semi_major”, where “semi_major” is the LocalName (from the org.opengis.util package) and “OGC” is the scope. The mechanism is similar to fully qualified names in Java packages.
It should always be possible to know if a particular name is an OGC’s name or a GeoTIFF one: just look at the scope. For our own transformation, we use “Geotools:” scope. If we find an official name from OGC later, we will add that “OGC:” scoped name.
Multiple names for Parameters
A single physical parameter can have more than one name. Each classification/parameter can have an arbitrary number of names. Actually they do have. For example (using again the “Mercator_1SP” classification), one can try the following from the command line:
java org.geotools.referencing.operation.DefaultMathTransformFactory Mercator_1SP
Geotools will tells you that it know all of the above names for this transformation:
Note the Geotools name is localised, so it may appears in another language depending on how you have your machine set up.
One can use any of those names. Geotools will recognizes “CT_Mercator” as well as “Mercator_1SP”. However, if one wants to be sure that he is looking for a GeoTIFF name and not an OGC name, we can always use the fully qualified name.
For example GeoTools:
One can use DefaultMathTransformFactory in order to experiment the names from the command line.
All projections have the following default parameters:
The “semi_major” and “semi_minor” parameters do not need to be specified in the projection section of WKT strings, since this information can be obtained from the GEOGCS.
Additional parameters are shown in the following table. Note that “latitude_of_origin” and “scale_factor” are usually default parameters, except in the Mercator and some conic projections.
Notes about projections in ESRI’s ArcGIS 8.x
“Geocentric_To_Ellipsoid” and “Ellipsoid_To_Geocentric”
“Molodenski” and “Abridged_Molodenski”