Here is one way to do it (maybe). Add this to your Jython library
def fire(rhscrn,tscrn,u10):
rhscrn = newUnit(rhscrn,"rhscrn","K")
tscrn = newUnit(tscrn,"tscrn","K")
u10 = newUnit(u10,"u10","K")
answer = 2*exp(1.524-0.0345*rhscrn+0.0338*tscrn+0.0234*u10*3.6)
return answer
The create a formula. See section 4.2.1 of the workshop material.
See attached PNG.
-Julien
> Hi Julien,
>
> Thanks for the feedback. It seems my assumption that it was an IDV unit
> panic were correct. I don't know of a quick way to simply "change" the units
> as you suggest within IDV. I could do it by modifying the headers I suppose
> but for extremely large data sets (the results are typically about 2 Gb) it
> becomes problematic and more trouble than its worth, especially when IDV's
> main purpose (for most I think) is a quick way to visualise data. If you do
> find a workaround however please let me know.
>
> Eventually I'll be scripting some animations with NCL graphics and when it
> comes to scripting it wouldn't be a problem as you say to simply rename a
> unit. I could be wrong but I'm fairly sure NCL and other NetCDF capable
> software would continue to process an arithmetic formula even if it didn't
> understand the units. It's almost as though a simple "unit panic exception"
> needs to be written into IDV so that when it decides "these units are
> nonsensical" it thinks "OK, these are the results but I have no idea what the
> unit is!" instead of "Oh my I can't deal with this, I need to stop now,
> you're on your own!".
>
> Regards,
>
> Simon.
>
>
> -----Original Message-----
> From: Unidata IDV Support [mailto:address@hidden]
> Sent: Wednesday, February 16, 2011 7:18 AM
> To: Simon Metcalf
> Cc: address@hidden
> Subject: [IDV #ZTF-373299]: IDV formula failing, unit problems?
>
> Hi Simon,
>
> I can reproduce this problem. I understand that the unit is unitless from the
> physics point of view, but the IDV does not see it that way. rhscrn tscrn and
> u all have units associated with them which makes the IDV/ViSAD blow up. I am
> still looking into a solution / workaround, but that is where I am at. One
> way to kludge it, maybe, is to make rhscrn tscrn and u all the same unit, say
> temperature.
>
> -Julien
>
> > Hi Julien,
> >
> > I've uploaded the file along with the formula that has the parameter names
> > contained in the data so all you have to do is add the formula. The
> > formula is not a real variable but a unit-less index that defines the
> > relationship between some ground-level prognostics affecting fire danger.
> > I assume this is why it's having unit problems but I could be wrong. It
> > should be able to produce a result even if it can't identify a sensible
> > unit.
> >
> > 2*exp(1.524-0.0345*rhscrn+0.0338*tscrn+0.0234*u10*3.6)
> >
> > Only two time steps are included to keep the file size down.
> >
> > Regards,
> >
> > Simon.
> >
> > -----Original Message-----
> > From: Unidata IDV Support [mailto:address@hidden]
> > Sent: Tuesday, February 15, 2011 3:44 AM
> > To: Simon Metcalf
> > Cc: address@hidden
> > Subject: [IDV #ZTF-373299]: IDV formula failing, unit problems?
> >
> > Hi Simon.
> >
> > In order, to better diagnose this problem, would it be possible to
> > upload the ccam33S147E08km.nc here:
> > http://motherlode.ucar.edu/repository/alias/idvupload
> >
> > Let us know when it is uploaded.
> >
> > Also, tell us a bit more about what you are trying to do with these data so
> > that we can give you a better answer.
> >
> > Thanks.
> >
> > -Julien
> >
> > > Full Name: Simon Metcalf
> > > Email Address: address@hidden
> > > Organization: NSW Rural Fire Service Package Version: 2.9u3 build
> > > date:2011-01-14 00:05 UTC Operating
> > > System: Windows XP
> > > Hardware: Java: home: C:\Program Files\IDV_2.9u3\jre version:
> > > 1.6.0_20
> > > j3d:1.5.2 fcs (build4) Description of problem: Creating display:
> > > Color-Shaded Plan View
> > > visad.UnitException: visad.UnitException org.python.core.PyException
> > >
> > > Hi, I'm having trouble getting IDV to display the following formula:
> > >
> > > 2*exp(1.524-0.0345*RH+0.0338*T+0.0234*WS*3.6)
> > >
> > > The error above seems to indicate that it's having trouble identifying a
> > > correct unit for the results, which is not surprising because the formula
> > > is supposed to create a unit-less index value. Can you assist with
> > > identifying the problem with IDV and if there is a workaround solution?
> > >
> > > Regards, Simon.
> > >
> > > ******************
> > > Stack trace:
> > > Traceback (innermost last):
> > > File "<string>", line 1, in ?
> > > at visad.RealType.binary(RealType.java:473)
> > >
> > > at visad.FunctionType.binary(FunctionType.java:270)
> > >
> > > at visad.FunctionType.binary(FunctionType.java:270)
> > >
> > > at visad.DataImpl.binary(DataImpl.java:138)
> > >
> > > at visad.DataImpl.add(DataImpl.java:179)
> > >
> > > at visad.DataImpl.__add__(DataImpl.java:1393)
> > >
> > > at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> > >
> > > at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
> > >
> > > at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
> > >
> > > at java.lang.reflect.Method.invoke(Unknown Source)
> > >
> > >
> > > visad.UnitException: visad.UnitException
> > >
> > >
> > >
> >
> >
> > Ticket Details
> > ===================
> > Ticket ID: ZTF-373299
> > Department: Support IDV
> > Priority: Normal
> > Status: Closed
> >
> > RFS Disclaimer:
> > This email message is intended only for the addressee(s) and contains
> > information which may be confidential. If you are not the intended
> > recipient, please notify the sender and delete this email and any copies or
> > links to this email completely and immediately from your system. Views
> > expressed in this message are those of the individual sender, and are not
> > necessarily the views of the NSW Rural Fire Service.
> >
>
>
> Ticket Details
> ===================
> Ticket ID: ZTF-373299
> Department: Support IDV
> Priority: Normal
> Status: Open
>
>
Ticket Details
===================
Ticket ID: ZTF-373299
Department: Support IDV
Priority: Normal
Status: OpenAttachment:
fire.png
Description: PNG image
