# Re: [idvusers] What is the best way to iterate over a 3d grid using Jython?

• To: Paul Graham <meteorpaul@xxxxxxxxx>
• Subject: Re: [idvusers] What is the best way to iterate over a 3d grid using Jython?
• From: Joleen Feltz <joleenf@xxxxxxxxxxxxx>
• Date: Tue, 10 Dec 2013 08:19:58 -0600
```Hi,

This question might be out of place, but I have been wondering for a long time
how to create a cross section of potential temperature based off a satellite
generated temperature and humidity retrieval.  I have been able to create a
single level flat field, but never a cross section.  It seems to me that this
is the approach I want to take.  However, the field that I have does not appear
to be a proper flat field for the extractPressureFromNWPGrid function.  What
are the requirements?  The field as far as I know is T(lon,lat,P):

FunctionType:
Domain has 3 components:
0. RealType: longi[unit:degrees_east]
0.   Name = longi[unit:degrees_east]
0.   Unit: degrees_east
1. RealType: lati[unit:degrees_north]
1.   Name = lati[unit:degrees_north]
1.   Unit: degrees_north
2. RealType: Plevs[unit:hPa]
2.   Name = Plevs[unit:hPa]
2.   Unit: hPa
Range:
RealType: TAir[unit:K]
Name = TAir[unit:K]
Unit: K

Joleen

On Dec 9, 2013, at 3:59 PM, Paul Graham wrote:

> Hi Tom,
>
> Thanks for your help.  I figured out a method after some experimentation
> and realised I could not use the visad logic.  My algorithm works
> point-wise, which requires having to step through each point individually.
> Essentially, I modified existing code for substitution, found in IDV's
> Jython library:
>
> def wetbulb(temp,dewpt):
>   from java.lang import Math
>   tempData = temp.clone();
>   dewptData = dewpt.clone();
>   presData = extractPressureFromNWPGrid(tempData);
>   wetbulbData = temp.clone();
>   if (GridUtil.isTimeSequence(tempData)):
>      for t in range(tempData.getDomainSet().getLength()):
>         tempValues = tempData[t]
>         dewptValues = dewptData[t]
>         presValues = presData[t]
>         wetbulbRangeObj = wetbulbData.getSample(t)
>         newValues = wetbulbRangeObj.getFloats(0)
>         print "Processing wetbulb temperature for time ", t
>         for i in range(len(tempValues)):
>            if(str(float(tempValues[i].getValue()))!='nan'):
>               newValues[0][i] =
> findwetbulb(kelvinToCelcius(tempValues[i].getValue()),kelvinToCelcius(dewptValues[i].getValue()),presData[i].getValue())
>         wetbulbRangeObj.setSamples(newValues,1)
>   wetbulbData = newUnit(noUnit(wetbulbData),'Wetbulb temperature in
> celcius','C')
>   return wetbulbData
>
>
> Paul
>
>
>
> On 10 December 2013 01:12, Tom Whittaker <whittaker@xxxxxxxx> wrote:
>
>> Hi Paul --
>>
>> If your function has no logic that needs to be applied to each point,
>> then if the data were read in via the IDV they would be "VisAD Data
>> objects" and you should just be able to do something like:
>>
>> a = b + c - d
>>
>> where "b", "c" and "d" are 3D Data objects (or maybe 4D if they
>> include "time") and it will do the computation on every point. and put
>> the result in "a" (creating a new Data object with characteristics
>> like that of "b" (the first object in the computation).
>>
>> If you have logic, then you might have to iterate over every point...I
>> say "might" because sometimes some of the built-in methods like "mask"
>> can be used to simulate logic.
>>
>> Hope that helps.
>>
>> tom
>>
>>
>>
>> On Sun, Dec 8, 2013 at 9:39 PM, Paul Graham <meteorpaul@xxxxxxxxx> wrote:
>>> Hi IDV'ers,
>>>
>>> I have written a Jython function which takes temperature, dewpoint and
>>> pressure as arguments and evaluated at each point in a 3d domain to
>>> calculate the wet bulb temperature.  What is the best way using Jython to
>>> iterate over my domain so I can set the wetbulb result for each point?
>>> Eg. wetbulbresult[i][j][k] =
>>> findwetbulb(temperature[i][j][k],dewpoint[i][j][k],pressure[i][j][k]),
>>> where i,j are subscripts for the latitude and longitude and k for the
>>> height.
>>>
>>>
>>> Paul
>>> _______________________________________________
>>> idvusers mailing list
>>> idvusers@xxxxxxxxxxxxxxxx
>>> For list information, to unsubscribe, visit:
>> http://www.unidata.ucar.edu/mailing_lists/
>>
>>
>>
>> --
>> Tom Whittaker
>> Space Science & Engineering Center (SSEC)
>> Cooperative Institute for Meteorological Satellite Studies (CIMSS)
>> 1225 W. Dayton Street