20030808:Questions in creating formula in IDV

> > To: address@hidden
> > From: =?big5?q?LEONG=20IVAN?= <address@hidden>
> > Subject: Re: 20030807: Questions in creating formula in IDV!!
> > Organization: UCAR/Unidata
> > Keywords: 200308080256.h782uDLd018245  IDV formula

Ivan-

>       Thank you for your kindly aid. Actually I am
> using JMA nc data to do some research. I prefer the
> second method you suggested ( create a new formula
> which would pass in the parameters directly instead of
> having the prompting dialog). But, where can i get
> more information about the methods just like
> DerivedGridFactory.createLayerDifference
> (a, 500, 850) which can be run in IDV. Is that a
> interval function or mehtod in IDV. Is that come from
> VisAD? Jython? 

This is a Java function within IDV's class DerivedGridFactory
which has javadoc at:

http://www.unidata.ucar.edu/community/committees/metapps/docs/ucar/unidata/data/grid/DerivedGridFactory.html

As you've found the formula/diagnostics portion of the IDV
is not well documented and flushed out.  Our plan is to
develop a library of standard functions that can be used
in formulas.   The code (and documentation) is just not
there yet.

In your case, we could create a Jython wrapper around
this method like:

# Create a difference of the values of two layers of a grid
# @param a    grid to use
# @param b    top of layer (double value in units of vertical coordinate)
# @param c    bottom of layer (double value in units of vertical coordinate)
def layerDiff(a, b, c):
    from ucar.unidata.data.grid.DerivedGridFactory import *
    return createLayerDifference(a,b,c)

and then in the formula, you could call layerDiff(a,500,850)
and it would be hidden that this is coming from
the Java method (and shorter to type).

So, you could use the methods in DerivedGridFactory as well
as the standard Jython functions.  If there is a particular
function you'd like help with, let us know.

> Please give me some tips. Thanks a lot!

We will be updating our documentation with the next release and
will make sure to focus on documenting the diagnostic capabilities
more.  For now, the best docs we have are in the "Doing more"
section of the User Guide.

Don