[ncl-talk] Pixel to Lat/Lon

[Dave Allured - NOAA Affiliate]

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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