[ncl-talk] Pixel to Lat/Lon

[Dennis Shea]

IMHO: The script is working correctly. However, there is a mismatch between
the
the user's VERY high resolution (0.15 degrees) 'target grid' and the
resolution of the swath data points.

re:

 nlat=1200
 nlon=2400

defines a grid with spacing 0.15 degrees. VERY high resolution

====

I have no idea what the rationale for the '400' used for GBIN and GKNTwas
based upon.

 GBIN  = new ( (/400,nlon/), float )
 GKNT = new ( (/400,nlon/), integer )

=====

The binning algorithm looks at each swath lat/lon location. It finds the
target grid box that 'surrounds'  the current swath lat/lon location.

If there are target grid boxes which do not surround the swath grid poins,
then they are returned as missing (_FillValue). Hence, the 'fractured' look
of the plot.

D





On Thu, Jul 13, 2017 at 2:52 PM, Mary Haley <haley at ucar.edu> wrote:

> Hi Ipsita,
>
> I'm not sure what you mean by " even though the plot is not coming with a
> clear contours. "
>
> The plot you included doesn't look particularly wrong, so can you explain
> what you were expecting?
>
> The script you attached does not include any plotting code, so I can't
> help you much there.
>
> Can you be more specific about the problem?  Also, it would really help if
> you can provide the data and the plotting script in the usual way (ftp).
>
> Thanks,
>
> --Mary
>
>
>
>
> On Thu, Jul 13, 2017 at 7:04 AM, Ipsita Putatunda <
> ipsita.putatunda at gmail.com> wrote:
>
>> Thank you Dave for your suggestions. I tried to plot the data, but it is
>> coming only if I plot setting resource "RasterFill", and even though the
>> plot is not coming with a clear contours. Don't know where I am making
>> mistake. I tried to regrid the data using "triple2grid" but then all the
>> values are coming undefined. I am attaching herewith my script and the
>> figure I have got after plotting. Any help will be appreciated.
>> Thanks in advance.
>>
>> Ipsita
>>
>>
>> On Thu, Jul 13, 2017 at 4:19 AM, Dave Allured - NOAA Affiliate <
>> dave.allured at noaa.gov> wrote:
>>
>>> Ipsita,
>>>
>>> This HDF5 file has coordinate arrays Colatitude and Longitude.  The
>>> units of each are degrees, not pixels.  However, please notice two
>>> anomalies:
>>>
>>> 1.  The coordinates are packed with an unusual scale/offset packing
>>> scheme.  The packing parameters are in attributes Scale_Factor and
>>> Add_Offset, which are not CF standard attributes.  However, the intent is
>>> fairly clear.  To unpack each coordinate value, just multiply by the
>>> Scale_Factor.
>>>
>>> The Add_Offset's are zero in this case, and can therefore be ignored.
>>> That is good, so that we do not have to worry about whether the offset
>>> would be applied before or after the scale factor.
>>>
>>> This will produce colatitudes in the normal range 60 to 120 degrees, and
>>> longitudes in the normal range 0 to 360 degrees.
>>>
>>> 2.  I assume that the colatitudes conform to the current definition on
>>> Wikipedia.  You might confirm this with the data provider, if you wish.
>>> This definition is the number of degrees southward from the north pole.
>>> The colatitude values unpacked are in the range 60 to 120 degrees, which
>>> translate to 30 north to 30 south in normal latitude units.
>>>
>>> --Dave
>>>
>>>
>>> On Wed, Jul 12, 2017 at 12:08 AM, Ipsita Putatunda <
>>> ipsita.putatunda at gmail.com> wrote:
>>>
>>>> The Latitude (here Colatitude) and Longitude data are in pixels which
>>>> is -30 to 30 degree and 0 to 360 degree. Please find the file I am
>>>> attaching herewith.
>>>>
>>>> Ipsita
>>>>
>>>> On Tue, Jul 11, 2017 at 10:30 PM, Dave Allured - NOAA Affiliate <
>>>> dave.allured at noaa.gov> wrote:
>>>>
>>>>> Ipsita,
>>>>>
>>>>> How is your input data georeferenced?  Does the input file include
>>>>> coordinate variables?  That is the most common way to get lats and lons for
>>>>> individual pixels.
>>>>>
>>>>> --Dave
>>>>> (Please reply to the mailing list.)
>>>>>
>>>>>
>>>>> On Tue, Jul 11, 2017 at 12:22 AM, Ipsita Putatunda <
>>>>> ipsita.putatunda at gmail.com> wrote:
>>>>>
>>>>>> Dear NCL users,
>>>>>>   I need help in converting pixels to Lat/Lon grid. Is there any
>>>>>> function or way in ncl for doing this operation? Please suggest.
>>>>>>
>>>>>> Thanks in advance,
>>>>>> Ipsita
>>>>>>
>>>>>
>>
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