ERA-Interim and regrid2 v. xdef/ydef

[Matt Jeglum]

I have been using the ERA-Interim dataset, and after running it through grib2ctl I get control files
that work, but do not include any sort of PDEF specification.  I am ultimately interested in
interpolating the 1.5 degree grid on the ERA-Interim to a higher resolution.  I have heard of two
methods to do this.  One is to use the regrid2 function, but since I am computer illiterate and the
other option is quite easy, I am avoiding that.  It seems possible to change the xdef and ydef
specifications in the ctl file to interpolate to the higher resolution to begin with.  All you would need
to change is the # of grid points and the increment.  This has worked for others but not for me, and I
suspect it may be due to the lack of PDEF.  Is this method legitimate? If so, anyone know the ERA-
Interim projection specs for PDEF?