[ncl-talk] How to correctly read in the merged CMORPH data usig NCL
Dennis Shea
shea at ucar.edu
Wed May 3 08:01:41 MDT 2017
Barry makes a good point about the using the "Little Endian" byte-order.
Another issue is the 'type' ,,, In my opinion, using "double" is likely
not correct. Having precipitation at (say) 12+ digits of precision is
rather silly.
I suggest that you do some very basic 'data exploration'.
For example: Look at min/max
You should do this type of thing on a regular basis.
You have:
setfileoption("bin","ReadByteOrder","LittleEndian")
rain = fbindirread(tim,0,(/nlat,nlon/),"double")
print("min="+min(rain)+" max="+max(rain))
Try:
setfileoption("bin","ReadByteOrder","BigEndian")
rain = fbindirread(tim,0,(/nlat,nlon/),"float")
print("min="+min(rain)+" max="+max(rain))
----
https://www.ncl.ucar.edu/Applications/
Under "Datasets", Click "High Res Precipitation"
There are several CMORPH examples.
The source of the files USA NCEP/CPC has documentation (
ftp://ftp.cpc.ncep.noaa.gov/precip/global_CMORPH/README.
cmorph.025deg_3-hourly) that states:
Each file is composed of 16 direct access binary
("big_endian")
Maybe CMA has a different data set. I do not know.
========================
cmorph_1.ncl
demonstrates how to
[1] Read the CMORPH binary files
[2] Create meta data
[3] Plot on global projection
--
For the China region
[1]
latS = 15.0
latN = 58.9
lonL = 70.0
lonR = 140.0
Two approaches to plot the China region:
res at mpMinLatF = latS ; range to zoom in on
res at mpMaxLatF = latN
res at mpMinLonF = lonL
res at mpMaxLonF = lonR
[2]
plot = gsn_csm_contour_map(wks, rain, res)
[3]
rain_china= rain({latS:latN},{lonL:lonr}) ; coordinate subscripting
res at gsnAddCyclic = False
plot = gsn_csm_contour_map(wks, rain_china, res)
=============================
If you are new to NCL, please read the excellent tutorial created by DKRZ
at:
https://www.ncl.ucar.edu/Document/Manuals/NCL_User_Guide/
Good Luck
On Tue, May 2, 2017 at 11:59 PM, wen <wenguanhuan at 163.com> wrote:
> Hi Barry，
> ny = 440，nx=700, which are "nlat" and "nlon" in the script of Yi Lu.
>
>
>
>
> --
> Best regards,
> Guanhuan Wen
>
> At 2017-05-03 13:17:32, "Barry Lynn" <barry.h.lynn at gmail.com> wrote:
>
> Hi Wen:
>
> What are nx,ny? Are they suppose to be the same values in the data read
> in and the data plotted?
>
> Are you sure about the little_endian definition?
>
> On Wed, May 3, 2017 at 6:16 AM, wen <wenguanhuan at 163.com> wrote:
>
>> Hi. The following script is able to read the data. I hope it work for
>> you.
>>
>>
>> setfileoption("bin","ReadByteOrder","littleEndian")
>> mfile = "1.grd"
>> rec = 0
>> crain = fbindirread(mfile,rec,(/ny,nx/),"float")
>> rec = 1
>> gsamp = fbindirread(mfile,rec,(/ny,nx/),"float")
>>
>>
>>
>> --
>> Best regards，
>> Guanhuan Wen
>>
>> 在 2017-04-30 12:07:44，"易路" <dg1225033 at smail.nju.edu.cn> 写道：
>>
>> Hi all,
>> I downloaed the merged CMORPH data from China Meteorological
>> Administration to get the hourly precipitation imformation, the suffix of
>> the data file is grd which is a standard format of the tool GrADS.
>> According to the associated ctl file of the grd file, I tried to write the
>> NCL script to read it but can't get the right data, and I couldn't find out
>> the prolbems...
>>
>> So would you please help me to find out the problems ? Thanks very mcuh
>> for your precious time and kindness!
>>
>> Sincerely
>> Yi Lu
>>
>> ;;;;;;;;;;; the part of NCL script to read in the
>> precipitation ;;;;;;;;;;
>> tim = "1.grd"
>> setfileoption("bin","ReadByteOrder","LittleEndian")
>> rain = fbindirread(tim,0,(/nlat,nlon/),"double")
>>
>> nlat = 440
>> nlon = 700
>> r=new((/nlat,nlon/),"double")
>> k=0
>> do i = 0, nlat-1
>> do j = 0, nlon-1
>> r(i,j) = rain(nlat-1-i,j)
>> k = k+1
>> end do
>> end do
>>
>> lon = fspan(70.05,139.95,nlon)
>> lon!0 = "lon"
>> lon at units = "degrees_east"
>> lon at long_name = "longitude"
>>
>> lat = fspan(15.05,58.95,nlat)
>> lat!0 = "lat"
>> lat at long_name = "latitude"
>> lat at units = "degrees_north"
>>
>> r!0 = "lat"
>> r!1 = "lon"
>> r&lat = lat
>> r&lon = lon
>> r at units = "mm/hour"
>> r at long_name = "merged CMORPH data "
>> r at _FillValue = -999.00
>> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
>>
>>
>>
>>
>>
>>
>> 易路
>>
>> 南大邮件系统/学生/博士生/12级博士生
>>
>> 南京市汉口路22号
>>
>>
>>
>>
>>
>>
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>
>
> --
> Barry H. Lynn, Ph.D
> Senior Lecturer,
> The Institute of the Earth Science,
> The Hebrew University of Jerusalem,
> Givat Ram, Jerusalem 91904, Israel
> Tel: 972 547 231 170
> Fax: (972)-25662581
>
> C.E.O, Weather It Is, LTD
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