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[THREDDS #GAL-491903]: questions about projections and datum



Hi Shawn,

> I am an ITC student who used to work closely with OGC specifications. I
> learned from your website that Unidata will provide the data use in the
> Geosciences in the coming years. That is a thrilling news to me and I
> have been searched around the website for relative documents. It may due
> to my poor searching ability that I couldn't find descriptions about the
> datum and coordinate system for the data model you're using now. There
> is one illustration of the DOM, however, I can't get the idea of
> vertical transformation and the other one. It would be nice if you can
> give me a little bit heads-up about the datum and coordinate system
> issue because they are crucial for GIS data. Thank you very much in
> advance.

Our data comes in a variety of forms and they don't really have a consistent 
method for containing datum and coordinate system information. We have software 
that recognizes the different conventions the data are stored in and 
determining coordinate system information. Much of the data we deal with is 
quite low resolution from a GIS perspective and many, even most, do not specify 
a datum.

We are involved in a number of groups/projects that are working to standardize 
this kind of information:

1) CF (http://www.cgd.ucar.edu/cms/eaton/cf-metadata/CF-1.0.html) is a metadata 
convention for Climate and Forecast (CF) data that is stored in the netCDF file 
format. They are looking at various ways to encode this kind of information and 
are currently looking at WKT as an interim solution.

2) The GALEON project started as an OGC Interoperability Experiment. It has  
been working on mapping between netCDF data and OGC WCS. Our THREDDS WCS 
capabilities were developed out of this project.
 
> Oh, if you don't mind. I am extremely curious about how you convert the
> arbitrary grid shape into regular one when providing WCS in the latest
> version. Would you please give me a hint about this too? Thanks a
> million.

I'm not sure what you mean by arbitrary grid shape. All the gridded data that 
we are serving through WCS have projection information that allows us to 
provide all the information needed by WCS.

Hope this helps.

Ethan


Ticket Details
===================
Ticket ID: GAL-491903
Department: Support THREDDS
Priority: Critical
Status: Open


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