NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
Current content can be found at unidata.ucar.edu.

To learn about what's going on, see About the Archive Site.

data transformation questions

I have a netcdf file of an mm5 model output. One variable is max wind speed, defined over a 2d grid, with values every 3 hours. The nc file has CF conventions in place so IDV can display it.
I would like to perform two transformations on the data in order to display it in idv:
1 create a smaller area. the orig grid is say 100x100 and I want to view just say an inner box of 20x20. I know I can zoom in on the area but the mere presence of the full grid has influence on the contouring/display so I would prefer to clip the data first
2 the units from the model are ms-1. i would like to display (and contour) in knots.
I suspect that the first task cannot be done in IDV. I had hoped that NcML would provide some filtering leverage like this, but I haven't found it. 

The unit conversion can be done in IDV ??

Any help gratefully appreciated

Stuart Maclean