Re: Coordinate mapping conventions...

Joe Sirott (
Thu, 22 Oct 92 09:47:44 -0700

Hello all,

I've been following the discussion about coordinate mapping conventions with
interest. I have another proposal that I'd like to suggest.

It seems to me that support for components and data to coordinate mapping 
can be solved by adding a small extension to the netCDF language. Why not
add support for something analogous to C structures. For instance, we might
have the following definition:

	float u(lat,lon,depth);
	float v(lat,lon,depth);
	float w(lat,lon,depth);
	struct velocity { u,v,w };

All components of the structure would have to have the same number and
size dimensions. Components of a structure could be addressed in the
same way as the C language, i.e. velocity.u, velocity.v, and
velocity.w. Also, a new function to retrieve the components of a
structure would be added; something like:

	ncstructinq(int cdfid, int varid, char *name, int* ncomps,
		    int comps[]);


	cdfid = netCDF id
	varid = variable id
	name = variable name
	ncomps = number of components
	comps = vector of component ids

The problem of defining data to coordinate space transformations would also be
addressed by this extension. For instance, Rich Signell's example of
an ocean surface drifter could be handled by the following definition:

	Dimensions: size = 1000
		float lat(size);
		float lon(size);
		struct position { lat, lon };
		float temp(position);


Joe Sirott