Re: M3IOConvention

Hi Robert:

It would be simple to modify M3IOConvention.java to look for this
information, and pass the radius to the projection:

      new LambertAzimuthalEqualArea(lat0, lon0, 0.0, 0.0, 6370000.0);

I notice that the sample file i have does not have that info in it. I am 
cc'ing Todd Plessel, the original author, to see if he has any comments 
or wants to add this feature.

Regards,
John


On 1/28/2013 1:22 PM, Schmunk, Robert B. (GISS-611.0)[TRINNOVIM, LLC] wrote:
> John,
>
> A Panoply user had a problem with a small shift in the placement of a
> projected lon-lat grid in a netCDF dataset. The gridding uses the
> Lambert conformal conic grid, and the dataset was written using the
> M3IO convention. I got into the netCDF-Java source code for
> ucar.nc2.dataset.conv.M3IOConvention.java to see if I could get a
> better grip of what was going on and found that that class is looking
> for a grid type specified by the dataset's GDTYP global attribute.
> Further definition of the grid is determined by checking the XCENT,
> YCENT, P_ALP, and P_BET attributes.
>
> The problem that is arising is that there is apparently no way to
> pass along the value of the Earth radius used by the projected grid.
> M3IOConvention.java is not looking for the value and is defaulting to
> 6,371.229 km, but the grid in the problem dataset is based on a
> radius of 6370 km. (A very small diference, but the effect is visible
> in a plot a couple egrees on a side.) The dataset (and perhaps the
> M3IO format) do not include a single specific attribute for the Earth
> radius, but does include info about it in a FILEDESC global
> attribute, a very long string which includes "… EARTH RADIUS ASSUMED
> IN MCIP:  6370000.000 m …".
>
> Is it possible that in a coming update to the NJ libraries that
> M3IOConvention.java could be coded to look for this radius
> information in the FILEDESC attribute? Or do you have any suggestions
> on how one might otherwise deal with this non-default radius? The
> user who contacted me about this apparently has hundreds of similar
> files, so we're looking for a consistent gridding/plotting solution.
>
>
> rbs
>
>
> -- Robert B. Schmunk Webmaster / Senior Systems Programmer NASA
> Goddard Institute for Space Studies 2880 Broadway, New York, NY
> 10025