[ncl-talk] Pixel to Lat/Lon
Dennis Shea
shea at ucar.edu
Sun Jul 16 22:54:10 MDT 2017
The attached shows
[top] a plot of the raw data
[middle] plot from the bin_sum [avg] onto the original high res grid
[bottom] using 'poisson_grid_fill' and then using a do loop on [2] to
filter points outside the original swaths.
I do not recommend extrapolation beyond the original region. Extrapolation
is 'always' dangerous unless it is based upon physical principles.
See attached,
====
Please note using the one data file I have ... look at the max/min from the
original data and GBIN
Variable: data
Dimensions and sizes: [2383] x [51] <=== original
units : Watts/m**2
long_name : Flux_Longwave_TOA
_FillValue : 32767
(0) Flux_Longwave_TOA (Watts/m**2) : min=50 max=313.88 <=== original
=====
Variable: GBIN
Dimensions and sizes: [lat | 400] x [lon | 2400] <=== target grid
Coordinates:
lat: [-29.925..29.92501]
lon: [0.075..359.925]
Number Of Attributes: 3
units : Watts/m**2
long_name : BINNED: Flux_Longwave_TOA
_FillValue : 9.96921e+36
(0) BINNED: Flux_Longwave_TOA (Watts/m**2) : min=50 max=313.88 <===
Note
(0) GBIN: nmsg=849042 <=== large number of missing values
(0) -----
Variable: GKNT
Type: integer
Dimensions and sizes: [lat | 400] x [lon | 2400]
Coordinates:
lat: [-29.925..29.92501]
lon: [0.075..359.925]
Number Of Attributes: 2
long_name : BINNED COUNT: Flux_Longwave_TOA
_FillValue : -2147483647
(0) BINNED COUNT: Flux_Longwave_TOA : min=1 max=3 <=== Note
On Sun, Jul 16, 2017 at 12:36 PM, Ipsita Putatunda <
ipsita.putatunda at gmail.com> wrote:
> Hi all,
> Thanks a lot for your help. But I have one more doubt. I ran the script
> attached by Dennis (Both without any regridding, and with bin_avg), but the
> maximum value of Longwave_Flux_TOA is coming more than 1200 both the cases,
> where as the data definition is saying the range of the value is (0 to
> 500). Why is it so?
>
> Thanks,
> Ipsita
>
> On Fri, Jul 14, 2017 at 11:12 PM, Dave Allured - NOAA Affiliate <
> dave.allured at noaa.gov> wrote:
>
>> Ipsita et al,
>>
>> I think you can plot this swath data directly, without regridding. This
>> would require conforming arrays of 2-dimensional latitudes and longitudes.
>> But guess what? That's what we figured out two days ago. ;-)
>>
>> If this works, I think the plot would look better and plot faster. Sorry
>> I did not think of this sooner.
>>
>> --Dave
>>
>>
>> On Fri, Jul 14, 2017 at 7:46 AM, Dennis Shea <shea at ucar.edu> wrote:
>>
>>> Attached is a script that uses ESMF to regrid. Generating the weights is
>>> a bit slow.
>>>
>>> On Fri, Jul 14, 2017 at 12:59 AM, Ipsita Putatunda <
>>> ipsita.putatunda at gmail.com> wrote:
>>>
>>>> Hi Mary,
>>>> If I plot in "RasterFill" mode then only the plot is appearing, not
>>>> even I set "AreaFill" or "CellFill".
>>>> The plot is appearing something like fractured, not a smoothed one
>>>> (even though I put smoothing), I don't know why it is like so.
>>>>
>>>> Thanks in advance,
>>>> Ipsita
>>>>
>>>> On Fri, Jul 14, 2017 at 11:34 AM, Ipsita Putatunda <
>>>> ipsita.putatunda at gmail.com> wrote:
>>>>
>>>>> Hi Mary,
>>>>> I have uploaded my data file with my scripts through ftp.
>>>>>
>>>>> Ipsita
>>>>>
>>>>> On Fri, Jul 14, 2017 at 2:51 AM, Dennis Shea <shea at ucar.edu> wrote:
>>>>>
>>>>>> 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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>>>>>>
>>>>>
>>>>
>>>
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