Re: obtain values of a single contour

Great! Glad to hear you could get it working. FYI, I have fixed the problems I mentioned yesterday, so the next release will not require you to set trGridType to "TriangularMesh".
 -dave

On Apr 17, 2013, at 7:02 PM, <Mark.Collier@csiro.au> wrote:

> Hi Dave,
> Many thanks for the solution. With these ideas and some further development I could get what I wanted. Attached is the final plot. The difference between two of the contours is shown at the 300hPa level, the desired result.
> Regards,
> Mark.
> <tropoh_climdiff.png>
> On 17/04/2013, at 3:43 PM, David Brown <dbrown@ucar.edu> wrote:
>
>> Hi Mark,
>>
>> The immediate cause of the error message is that when you set gsnYAxisIrregular2Linear = True, the gsn code does an overlay behind
>> the scenes onto an "irregular" plot. This means that plot0 is no longer itself a contour plot. The contour plot id is available as an attribute of plot0.
>> So the get_isolines call needs be:
>>
>> isolines = get_isolines(plot0@contour,(/2.0/))
>>
>> However, it turns out that there are still some issues with this scenario and get_isolines needs some more work. When not over a map, get_isolines is
>> returning values in a low-level coordinate system rather than as data coordinates. However, there is a workaround that should give you what you want:
>> Set trGridType = "TriangularMesh". In this mode it does return data coordinates and also it linearizes the YAxis without using the special gsnYAxisIrregularToLinear resource.
>> I am attaching a revised version of your plot that works. I also modified the polyline drawing code to draw a line on top of the
>> original contour line using the returned coordinate values to demonstrate that they do match. Note that if you only ask for one level get_isolines returns an array not a list.
>> Hope this helps.
>> -dave
>> <plot_davetest-new.ncl>
>>
>> On Apr 16, 2013, at 6:09 PM, <Mark.Collier@csiro.au> wrote:
>>
>>> Hi Dave,
>>> I put the script plot_davetest.ncl and input data file davetest.nc in the incoming area. I tried it under both 6.1.1 and 6.1.2 with same error.
>>>
>>> uname -a
>>> Linux dcc 2.6.18-348.3.1.el5 #1 SMP Mon Mar 11 19:39:25 EDT 2013 x86_64 x86_64 x86_64 GNU/Linux
>>>
>>> Regards,
>>> Mark.
>>> On 17/04/2013, at 5:57 AM, David Brown <dbrown@ucar.edu> wrote:
>>>
>>>> Hi Mark,
>>>> I'm sorry to hear you are having problems with this routine. I just ran a test using the plot value returned from
>>>> gsn_csm_contour as the input to get_isolines pretty much as you have it here. It ran without problems. I tried it both
>>>> with my development version of NCL on my mac and on our cluster using the release version of 6.1.2.
>>>>
>>>> I would be happy to take a look at your code (and sufficient data to get it to run) to see if there is some other factor
>>>> coming into play here. I think you know the upload routine but just in case for reference it is detailed at http://www.ncl.ucar.edu/report_bug.shtml.
>>>> -dave
>>>>
>>>>
>>>> On Apr 15, 2013, at 10:44 PM, <Mark.Collier@csiro.au> wrote:
>>>>
>>>>> Hi Dave,
>>>>> the interface looked simple enough but my best attempt gave:
>>>>>
>>>>> fatal:NhlGetIsoLines: invalid contourplot id
>>>>> fatal:NhlGetIsolines: error retrieving isolines
>>>>> fatal:["Execute.c":8128]:Execute: Error occurred at or near line 251 in file plot_tropoh_climdiff.ncl
>>>>>
>>>>> what I tried was:
>>>>>
>>>>> plot0=gsn_csm_contour(wks,clim1_hist_ea,conres2)
>>>>>
>>>>> isolines = get_isolines(plot0,(/2.0/))
>>>>>
>>>>> where plot0 renders normally, and it contains the 2.0 contour level.
>>>>>
>>>>> I'm using version 6.1.2
>>>>>
>>>>> Thanks,
>>>>> Mark.
>>>>> ________________________________________
>>>>> From: David Brown [dbrown@ucar.edu]
>>>>> Sent: Tuesday, 16 April 2013 4:01 AM
>>>>> To: Collier, Mark (CMAR, Aspendale)
>>>>> Cc: ncl-talk@ucar.edu
>>>>> Subject: Re: obtain values of a single contour
>>>>>
>>>>> Hi Mark,
>>>>> I recently created a function that will do what you want. It is available in NCL 6.1.1 and later. Check out:
>>>>>
>>>>> http://www.ncl.ucar.edu/Document/Functions/Built-in/get_isolines.shtml
>>>>>
>>>>> -dave
>>>>>
>>>>>
>>>>> On Apr 15, 2013, at 12:41 AM, <Mark.Collier@csiro.au> wrote:
>>>>>
>>>>>> Hi,
>>>>>> I plot a single unique contour of a 2d array using @cnLevels = val using the gsn_csm_contour function.
>>>>>>
>>>>>> is there a way of obtaining the x-y values of that line from the plot?
>>>>>>
>>>>>> Regards,
>>>>>> Mark.
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Received on Wed Apr 17 19:28:45 2013