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[udig-devel] Re: CRS - "Bursa wolf parameters required." 
Hi developers

(First of all: Could you PLEASE try to avoid too excessive citing. It makes your
mails hard to read.)

To the topic:

Dean wrote:
> Unfortunately it comes down to guessing sometimes or sending the data
> back to the provider and asking for the missing information.

Why not query missing/ambigous information from the user by offering a list of
suitable solutions, e.g. parameters?

Just in case you are interested: Some time ago I wrote a Swing widget that
allowed the user to select a CRS. The user could enter an EPSG number or select
a name from the list of available CRS. He/she could also create a custom CRS by
selecting a coordinate system, datum, ellipsoid and so on, again with the
possibility to use custom datums etc. and to enter the parameters manually.
Under the hood I called an installed EPSG database using JDBC to query available
CRS, datums, ellipsoids and so on. (Might only work under Windows.)
Then I used the information provided by the user to assamble the CRS, I believe,
by using the Geotools (2.0 branch!) EPSGFactory.

I remember this worked quite nicely for some CRS, but there were lots of
geodetic datums that GeoTools' EPSGFactory would not create (error thrown)
because it didn't support the kind of reprojection needed to translate it to
WGS84 geodetic datum. (The means of reprojections were specified in the EPSG
database but GeoTools would not be able perform lots of them.)

Anyway, if you are interested in the code, notify me. It might help, although it
will probably not solve exactly your problem.

---

Also some days ago there was a discussion about some data having a valid CRS and
some having none or an invalid/incomplete CRS.

A solution that I considered some time ago is to offer two map editors:
  - One that displays data without CRS by assuming that the coordinates
    correspond 1:1 to pixels.
    This editor could also be used f.e. to quickly manipulate raster/image data
    by ignoring the CRS information (if any) attached to the raster.
  - Another editor that displays data with CRS only and does on-the-fly-
    reprojection. (This editor needs to know "where on earth" the data is.)

So if data arrives with no or an incomplete/invalid CRS, it could get viewed in
the first editor only. If the user then adds missing CRS information, e.g. with
the widged I described above, it would then be suitable to get displayed in the
second editor with projection support.

Matthias Basler
c9bama@xxxxxxxxxxx



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