In the IDV, the underlying data are represented by VisAD Data objects.
An attribute of these Data objects is that they may contain units (as
defined by the udunits package). When arithmetically combining Data
objects, the units must be "compatible", just as in any equation.
Thus, when you add or subtract two Data objects, their units must be
compatible, and the values are transformed automatically. For
example, if you add something with units in degC to something with
units of degF, the result is "correct" since values were converted to
degK (as a "common unit") first.
Sometimes, we encounter ad-hoc formulas that need to combine just the
numeric values, without regards to units. The classic example for me
is "wind chill", but as we know there are others ;-)
In the IDV, one can either strip the units from the Data object prior
to combining, or extract the numeric values and work with them.
Since the units of a Data object are immutable (they cannot be
arbitrarily changed), it is necessary to create a 2nd object with the
desired units (or lack of units, in this case). Sometimes, it is
more expedient to extract the values and then use some of the JNumeric
(similar to NumPy) operators to combine the values. Otherwise, one
must usually iterate through all the values, which in Jython (Python)
can be slow.
There are several examples of doing this within the JPythonMethods
class in the visad.python package. In addition, several posting on
the McIDAS-V Forum have provided examples of doing such things.
I hope this helps, and I trust others with more experience will chime in...
tom
--
Tom Whittaker
Madison, WI USA
On Tue, Jan 14, 2014 at 2:35 PM, Brian Mapes <bmapes@xxxxxxxxxxxxxxx> wrote:
> I have no answers.
> More broadly, links to more info on units in IDV in general would be of
> interest to this reader.
> If list readers have knowledge to share.
>
>
> Sent from my iPad
>
>> On Jan 14, 2014, at 6:33 AM, "dzengiz.tafa@xxxxxxxxxx"
>> <dzengiz.tafa@xxxxxxxxxx> wrote:
>>
>> Hi
>>
>> Thank you very much for the advice. I have edited the portion what gave the
>> error by adding "make2D(item)"& i now get a result. The unit is also correct
>> (m²/s²)
>>
>> Now I would like to ask you one last question on this jython code. perhaps
>> you can help me with this one too.
>>
>> The original formula calculates the Storm relative helicity of a normal
>> storm motion
>> umotion = 0.75 * umean
>> vmotion = 0.75 * vmean
>>
>> I would now like to do the same jython, but applied to the deviant storm
>> motion of a right moving supercel.
>> the formula to calculate the deviant storm motion (u & v component) is this
>> one:
>>
>> umotion=((umean+(7.5/(shear))*vshear))
>> vmotion=((vmean-(7.5/(shear))*ushear))
>>
>> so plugged in the full jython it looks like this:
>>
>> def srh3km(u, v, top, bottom, unit=None):
>> u1000=getSliceAtLevel(u, 100000)
>> u950=getSliceAtLevel(u, 95000)
>> u900=getSliceAtLevel(u, 90000)
>> u850=getSliceAtLevel(u, 85000)
>> u800=getSliceAtLevel(u, 80000)
>> u750=getSliceAtLevel(u, 75000)
>> u700=getSliceAtLevel(u, 70000)
>> v1000=getSliceAtLevel(v, 100000)
>> v950=getSliceAtLevel(v, 95000)
>> v900=getSliceAtLevel(v, 90000)
>> v850=getSliceAtLevel(v, 85000)
>> v800=getSliceAtLevel(v, 80000)
>> v750=getSliceAtLevel(v, 75000)
>> v700=getSliceAtLevel(v, 70000)
>>
>> umean=layerAverage(u, bottom, top, unit)
>> vmean=layerAverage(v, bottom, top, unit)
>>
>> ushear=layerDiff(u, 50000, 100000, unit)
>> vshear=layerDiff(v, 50000, 100000, unit)
>>
>> shear=sqrt(ushear*ushear+vshear*vshear)
>>
>> ******************************************************
>> umotion=((umean+(7.5/(shear))*vshear)) <= Problem resides here: "unit
>> exception"
>> vmotion=((vmean-(7.5/(shear))*ushear)) <= Problem resides here: "unit
>> exception"
>> ******************************************************
>>
>> srh1=((make2D(u950)-make2D(umotion))*(make2D(v1000)-make2D(vmotion))-(make2D(u1000)-make2D(umotion))*(make2D(v950)-make2D(vmotion)))
>> srh2=((make2D(u900)-make2D(umotion))*(make2D(v950)-make2D(vmotion))-(make2D(u950)-make2D(umotion))*(make2D(v900)-make2D(vmotion)))
>> srh3=((make2D(u850)-make2D(umotion))*(make2D(v900)-make2D(vmotion))-(make2D(u900)-make2D(umotion))*(make2D(v850)-make2D(vmotion)))
>> srh4=((make2D(u800)-make2D(umotion))*(make2D(v850)-make2D(vmotion))-(make2D(u850)-make2D(umotion))*(make2D(v800)-make2D(vmotion)))
>> srh5=((make2D(u750)-make2D(umotion))*(make2D(v800)-make2D(vmotion))-(make2D(u800)-make2D(umotion))*(make2D(v750)-make2D(vmotion)))
>> srh6=((make2D(u700)-make2D(umotion))*(make2D(v750)-make2D(vmotion))-(make2D(u750)-make2D(umotion))*(make2D(v700)-make2D(vmotion)))
>>
>> sreh = srh1 + srh2 + srh3 + srh4 + srh5 + srh6
>>
>> return sreh
>>
>> When I run this jython code, the IDV gives me a "unit exception" error (no
>> further information).
>>
>> I tried to insert a "noUnit(shear)" or "noUnit(vshear)" but none of these
>> options work because when plugging in a noUnit() the IDV gives me the error
>> message "FlatField: RangeUnits must be convertable with RangeType default
>> Units".
>>
>> As you have helped me with the first question, can you provide an
>> explanation as to why this piece of jython doesn't work? or maybe edit the 2
>> lines or point me in the right direction?
>>
>> The whole purpose of these 2 forumulas (helicity of normal storm motion &
>> helicity of deviant storm motion) is to compare the 2 quantitatively for a
>> talk about supercels & severe weather. I would like to create the 2 maps &
>> lay them next to eachother for comparison purposes.
>>
>> Any help is much appreciated.
>>
>> Dzengiz
>>
>> ----- Oorspronkelijk bericht -----
>> Van: "Unidata IDV Support" <support-idv@xxxxxxxxxxxxxxxx>
>> Aan: "dzengiz tafa" <dzengiz.tafa@xxxxxxxxxx>
>> Cc: support-idv@xxxxxxxxxxxxxxxx
>> Verzonden: Maandag 13 januari 2014 23:57:56
>> Onderwerp: [IDV #XXB-920520]: formula: Storm relative helicity
>>
>> Dzengiz,
>>
>> I spent a while studying your Jython. The error occurs in the last few lines
>> when calculating srh1 through srh6. As far as I can tell, the script is
>> trying to do operations on incompatible types (2D versus 3D grids???). You
>> can confirm this (perhaps) by printing out some variables (e.g., u950 and
>> umotion). See what "FieldImpl" says. I am out of ideas on how to tackle this
>> problem. Yuan is in China this week, so I'll ask Monday. Alternatively, you
>> may wish to ask on the idvusers@xxxxxxxxxxxxxxxx list. Sorry I could not be
>> of more help.
>>
>> Best Wishes,
>> Unidata IDV Support
>>
>>
>>> Full Name: Dzengiz Tafa
>>> Email Address: dzengiz.tafa@xxxxxxxxxx
>>> Organization: Fastowarn
>>> Package Version: 4.1 build date:2013-08-02 18:38 UTC
>>> Operating System: Windows 7
>>> Hardware: Java: home: C:\Program Files\IDV_4.1\jre version: 1.6.0_43
>>> j3d:1.5.2 fcs (build4)
>>> Description of problem: Hi
>>>
>>> I am trying a formula which calculates the storm relative helicity between
>>> 1000 & 700mb, using the folowing code:
>>>
>>> def srh3km(u, v, top, bottom, unit=None):
>>> u1000=getSliceAtLevel(u, 100000)
>>> u950=getSliceAtLevel(u, 95000)
>>> u900=getSliceAtLevel(u, 90000)
>>> u850=getSliceAtLevel(u, 85000)
>>> u800=getSliceAtLevel(u, 80000)
>>> u750=getSliceAtLevel(u, 75000)
>>> u700=getSliceAtLevel(u, 70000)
>>> v1000=getSliceAtLevel(v, 100000)
>>> v950=getSliceAtLevel(v, 95000)
>>> v900=getSliceAtLevel(v, 90000)
>>> v850=getSliceAtLevel(v, 85000)
>>> v800=getSliceAtLevel(v, 80000)
>>> v750=getSliceAtLevel(v, 75000)
>>> v700=getSliceAtLevel(v, 70000)
>>>
>>> umean=layerAverage(u, bottom, top, unit)
>>> vmean=layerAverage(v, bottom, top, unit)
>>>
>>> ushear=layerDiff(u, 50000, 100000, unit)
>>> vshear=layerDiff(v, 50000, 100000, unit)
>>>
>>> shear=sqrt(ushear*ushear+vshear*vshear)
>>>
>>> umotion=umean*0.75
>>> vmotion=vmean*0.75
>>>
>>> srh1=((u950-umotion)*(v1000-vmotion)-(u1000-umotion)*(v950-vmotion))
>>> srh2=((u900-umotion)*(v950-vmotion)-(u950-umotion)*(v900-vmotion))
>>> srh3=((u850-umotion)*(v900-vmotion)-(u900-umotion)*(v850-vmotion))
>>> srh4=((u800-umotion)*(v850-vmotion)-(u850-umotion)*(v800-vmotion))
>>> srh5=((u750-umotion)*(v800-vmotion)-(u800-umotion)*(v750-vmotion))
>>> srh6=((u700-umotion)*(v750-vmotion)-(u750-umotion)*(v700-vmotion))
>>>
>>> sreh=srh1+srh2+srh3+srh4+srh5+srh6
>>>
>>> return sreh
>>>
>>> --
>>>
>>> When trying this formula I get the following error message:
>>> Creating display: Color-Filled Contour Plan View
>>> visad.TypeException: visad.TypeException: FunctionType.binary: types don't
>>> match
>>> FunctionType.binary: types don't match
>>>
>>> I need the SREH to work before I can implement the Supercel composite
>>> parameter and significant tornado parameter, since they both contain the
>>> SREH parameter.
>>>
>>> I really don't know what I am doing wrong, since the formula should work.
>>> Is it possible to correct the code or explain what I am doing wrong? Ive
>>> been trying for days now (to no avail). I have based this formula on the
>>> one found on this url (grads)
>>>
>>> http://www.saakeskus.fi/grads-scripts/63-storm-relative-helicity-0-3km
>>>
>>> Any help is much appreciated.
>>>
>>> Best regards,
>>> Dzengiz
>>>
>>> ******************
>>> Stack trace:
>>> visad.TypeException: FunctionType.binary: types don't match
>>> at visad.FunctionType.binary(FunctionType.java:283)
>>> at visad.DataImpl.binary(DataImpl.java:138)
>>> at visad.DataImpl.subtract(DataImpl.java:192)
>>> at visad.DataImpl.__sub__(DataImpl.java:1400)
>>> 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)
>>> at
>>> org.python.core.PyReflectedFunction.__call__(PyReflectedFunction.java:186)
>>> at
>>> org.python.core.PyReflectedFunction.__call__(PyReflectedFunction.java:204)
>>> at org.python.core.PyObject.__call__(PyObject.java:404)
>>> at org.python.core.PyObject.__call__(PyObject.java:408)
>>> at org.python.core.PyMethod.__call__(PyMethod.java:124)
>>> at org.python.core.PyMethod.__call__(PyMethod.java:115)
>>> at org.python.core.PyObjectDerived.__sub__(PyObjectDerived.java:187)
>>> at org.python.core.PyObject._basic_sub(PyObject.java:2119)
>>> at org.python.core.PyObject._sub(PyObject.java:2105)
>>> at org.python.pycode._pyx199.srh3km$7(<string>:70)
>>> at org.python.pycode._pyx199.call_function(<string>)
>>> at org.python.core.PyTableCode.call(PyTableCode.java:165)
>>> at org.python.core.PyBaseCode.call(PyBaseCode.java:301)
>>> at org.python.core.PyBaseCode.call(PyBaseCode.java:174)
>>> at org.python.core.PyFunction.__call__(PyFunction.java:350)
>>> at org.python.pycode._pyx200.f$0(<string>:1)
>>> at org.python.pycode._pyx200.call_function(<string>)
>>> at org.python.core.PyTableCode.call(PyTableCode.java:165)
>>> at org.python.core.PyCode.call(PyCode.java:18)
>>> at org.python.core.Py.runCode(Py.java:1261)
>>> at org.python.core.__builtin__.eval(__builtin__.java:484)
>>> at org.python.core.__builtin__.eval(__builtin__.java:488)
>>> at org.python.util.PythonInterpreter.eval(PythonInterpreter.java:190)
>>> at ucar.unidata.data.DerivedDataChoice.getData(DerivedDataChoice.java:787)
>>> at ucar.unidata.data.DataChoice.getData(DataChoice.java:637)
>>> at ucar.unidata.data.DataInstance.getData(DataInstance.java:243)
>>> at ucar.unidata.data.DataInstance.getData(DataInstance.java:207)
>>> at ucar.unidata.data.grid.GridDataInstance.init(GridDataInstance.java:206)
>>> at ucar.unidata.data.grid.GridDataInstance.<init>(GridDataInstance.java:163)
>>> at ucar.unidata.data.grid.GridDataInstance.<init>(GridDataInstance.java:144)
>>> at
>>> ucar.unidata.idv.control.GridDisplayControl.doMakeDataInstance(GridDisplayControl.java:284)
>>> at
>>> ucar.unidata.idv.control.DisplayControlImpl.initializeDataInstance(DisplayControlImpl.java:3224)
>>> at
>>> ucar.unidata.idv.control.DisplayControlImpl.setData(DisplayControlImpl.java:3206)
>>> at
>>> ucar.unidata.idv.control.PlanViewControl.setData(PlanViewControl.java:641)
>>> at
>>> ucar.unidata.idv.control.ContourPlanViewControl.setData(ContourPlanViewControl.java:194)
>>> at ucar.unidata.idv.control.PlanViewControl.init(PlanViewControl.java:471)
>>> at
>>> ucar.unidata.idv.control.DisplayControlImpl.init(DisplayControlImpl.java:1421)
>>> at
>>> ucar.unidata.idv.control.DisplayControlImpl.init(DisplayControlImpl.java:1106)
>>> at
>>> ucar.unidata.idv.ControlDescriptor.initControl(ControlDescriptor.java:986)
>>> at ucar.unidata.idv.ControlDescriptor$1.run(ControlDescriptor.java:911)
>>> at ucar.unidata.util.Misc$3.run(Misc.java:1251)
>>
>>
>> Ticket Details
>> ===================
>> Ticket ID: XXB-920520
>> Department: Support IDV
>> Priority: Normal
>> Status: Open
>>
>> _______________________________________________
>> idvusers mailing list
>> idvusers@xxxxxxxxxxxxxxxx
>> For list information, to unsubscribe, visit:
>> http://www.unidata.ucar.edu/mailing_lists/
>
> _______________________________________________
> idvusers mailing list
> idvusers@xxxxxxxxxxxxxxxx
> For list information, to unsubscribe, visit:
> http://www.unidata.ucar.edu/mailing_lists/
--
Tom Whittaker
Madison, WI USA
