[Fwd: Question about Coordinate System]

[Shawn Chen]

Hi, John,

I forwarded the idea as you suggested. Looking forward to the future
discussions.
Thanks for the prompt reply.

Cheers
Shawn


On 06/02/07, John Caron <caron at unidata.ucar.edu> wrote:
>
> Hi Shawn:
>
> John Caron wrote:
> >
> >
> > -------- Original Message --------
> > Subject: Question about Coordinate System
> > Date: Tue, 6 Feb 2007 16:03:36 +0100
> > From: Hsiang Yun Chen <chen14742 at itc.nl>
> > Reply-To: Hsiang Yun Chen <chen14742 at itc.nl>
> > Organization: UCAR/Unidata
> > To: <netcdfgroup at unidata.ucar.edu>
> >
> > Hi, Listers.
> >
> > I have a question of coordinate system after going through available
> > documents. Correct me if I am wrong.
> > Accodring to the CF-Convnetions, parameters such as projection
> > approaches (eg. Lambert_Conformal_projection) are specified. However, I
> > find no information about the DATUM.  Although it is assumed to be
> > WGS84, there is possiblity for data in other datum such as  Bessel-1841
> > specified in RT90. My question is, why not make the DATUM as a standard
> > parameter? With all the effort being made by ncML, the inconsistency
> > with other correctly geo-referencing dataset is still possible due to
> > the lack of DATUM parameter. Am i naive or missing/misunderstanding
> > something on the issue?
>
> this is definitely a shortcoming in CF-Conventions. Would you like to post
> your comments to that mailling list? you have to join first:
> http://www.cgd.ucar.edu/mailman/listinfo/cf-metadata
>
> >
> > ps. some ideas about ncML and netCDF, please correct me if I am wrong
> > One crucial point is that the ncML is the metadata of netCDF files.
> > Information in ncML is orginated from netCDF. It's true that users can
> > edit ncML to make it more complete, however, it still depends on the
> > header of netCDF.  Suppose, a user trying to create a data in his
> > national coordinate system (eg. RT90) using CF-Conventions.  The user
> > specified the projections and relevant parameters. It seems fine at
> > first. However, when the data is distributed and people who download the
> > data can't be able to know that the datum is Bessel-1841 which specified
> > in RT90. The system would transfer the coordinate system using WGS84 as
> > datum.  That, eventually, would lead to inconsistency with other data.
>
>
> You can add/change metadata using NcML. The Java library can read the NcML
> file, which points to the original netcdf file. The C library will
> eventually be able to do this also. To distribute the modifications as a
> netcdf file, you will have to rewrite the netcdf file, which can be easily
> done with the Java library.
>
> John
>
>
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-- 
I have a thing about first impressions.