[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[IDV #HJG-656532]: Derived quantities in formulas

This archive contains answers to questions sent to Unidata support through mid-2025. Note that the archive is no longer being updated. We provide the archive for reference; many of the answers presented here remain technically correct, even if somewhat outdated. For the most up-to-date information on the use of NSF Unidata software and data services, please consult the Software Documentation first.

  • Subject: [IDV #HJG-656532]: Derived quantities in formulas
  • Date: Fri, 02 Apr 2010 08:53:15 -0600
Hans,
Sorry but this support request slipped through the cracks.

> 
> I am plotting wind barbs from gridded point data (METARs) using the
> following formula:
> 
> 
> 
> makeVector(newName(-D1*sin(D2), "U"),newName(-D3*cos(D4), "V"))
> 
> 
> 
> It is my understanding that by using the operand names D1, D2, D3 etc,
> ticking the "Create derived quantities.." box under the "Derived" tab in the
> Formula Editor, and then specifying the data parameter names in the
> Parameters box ("SPD,DIR,SPD,DIR"), IDV should be able to bound the formula
> operands with the real data parameters on its own. However, IDV keeps asking
> what D1, D2 etc should be associated with every time I use the formula.
> 
> 
> 
> How do I get IDV to understand the operand bindings to the data parameters?
> 
> 

First of all - you don't need to do SPD,DIR,SPD,DIR you could have a formula 
like:
makeVector(newName(-D1*sin(D2), "U"),newName(-D1*cos(D2), "V"))

and match on the parameters: SPD,DIR

Now, if this formula is used to automatically create a derived quantity when you
load in a grid with speed and dir fields then the D1,D2,...,DN will get bound
to the fields in the grid.

However, if this formula is also to be used by the  end user then it shows up
in the Formulas and if you evaluate it you need to select appropriate fields
from a grid,  just like any other formula.

-Jeff


Ticket Details
===================
Ticket ID: HJG-656532
Department: Support IDV
Priority: Critical
Status: Closed