Re: [Geotools-gt2-users] Coordinate Transform

[Martin D. <mar...@ge...>]

Andrea Aime a écrit :
> They do use "+nadgrids=@null". One question thought... were is one
> supposed to specify that parameter in WKT? I need to be able and specify
> it somewhere, because the google crs is a custom one, and we specify it
> in a property file that backs epsg-ext, otherwise I won't be able
> to use it in GeoServer (anyways, being able to use it from code it's
> a good start).

The is no place where we can specify something like "nadgrids" in the WKT format
currently understood by GeoTools. Does this parameter refers to the NADCON grid
used for transformations from NAD27 to NAD83/WGS84 datum? If so, I would be a
little bit surprised that saying "No NADCON grid" means "no sphere to ellipsoid
transforms", since NADCON is specific to North America. More than that, it is
specific to transformations between 2 specific datum - it doesn't sound like a
generic way to said "no sphere to ellipsoid transforms". GeoTools do the
conversion without NADCON grid, otherwise what should do peoples outside North
America?

However, I just though about a possible way to said "no sphere to spheroid"
transform using standard WKT syntax; no extension - provided that we make
Geotools a little bit more intelligent. I'm writing a JIRA task right now.


> Proj4 uses a special parameter in WKT, "EXTENSION", but apparently
> the gt2 wkt parser cannot handle it (at least, I think last time
> I tried the wkt parser threw an error stating the parameter wasn't
> recognized... not so sure thought, I may be mistaken).
> For more examples see:
> http://www.spatialreference.org/ref/user/google-projection/
> http://www.spatialreference.org/ref/user/google-projection/ogcwkt/


Yes I can confirm the GeoTools WKT parser doesn't understand EXTENSION[...]. If
there is a need for it, this is an other JIRA task we could open.
EXTENSION[name, value] can probably be treated in a very similar way than
PARAMETER[name, value], maybe with the exception that it doesn't need to be
declared in the MathTransform provider.

	Martin