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[IDV #YHK-550263]: formulas on 2D grids

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  • Subject: [IDV #YHK-550263]: formulas on 2D grids
  • Date: Mon, 09 Feb 2009 12:59:18 -0700
Hi Steve-

> I am trying to do something simple, but I might be missing
> something... using IDV 2.6u1 on Mac.
> 
> Dewpoint is not currently output at 2 m in the GFS CONUS, and I would
> like to calculate it.
> 
> I create a simple formula (will get fancier later)
> 
> Name: Dewpoint from 2D temp and rh
> Formula: T-(100-RH)/5
> 
> Save.
> 
> When I go to use the formula with real data, contour plan view, select
> T (@hagl) and RH (@hagl) from the CONUS GFS fields, and get "Creating
> display: Contour Plan View
> org.python.core.PyException".
> 
> Any thoughts?

If you click on the Show Details button on the error dialog and
scroll down to the bottom, the exception is:

visad.UnitException: visad.UnitException

The problem is that you are trying to subtract RH (%) from
T (degrees something).  The IDV does not ignore units so
you are trying to subtract two incompatible quantities.
(That would be a good unit exercise for your students to see
what they would do. ;-))

You have two options:

1) add aliases for Temperature_height_above_ground and
Relative_humidity_height_above_ground to T and RH respectively
using the Tools->Alias Editor menu.  Then reload the grid to
pick this up automatically (and from then on).

2) Use the same formula as the 3D grid uses:

DerivedGridFactory.createDewpoint(T,RH)

and select the T and RH parameters from the dialog.

Don Murray


Ticket Details
===================
Ticket ID: YHK-550263
Department: Support IDV
Priority: Normal
Status: Open