[ncl-talk] How to get the regional data of SMAP L4 *(HDF5 format)
Dennis Shea
shea at ucar.edu
Fri Dec 15 10:03:02 MST 2017
What Mary wrote is generally correct ... Specifically:
========================
You are trying to extract the region from your HDF5 data by using
coordinate subscripting.
*Coordinate subscripting can only be done on rectilinear data*, *which is
data represented by one-dimensional lat/lon arrays that are the same length
as their corresponding dimension.*
Your data is likely curvilinear, which means your data is represented by
two-dimensional lat/lon arrays. I say this because in your code it looks
like you are extracting 2D lat/lon arrays:
lat2d = f->cell_lat
lon2d = f->cell_lon
nSmapLat = dimsizes(lat2d(:,0))
nSmapLon = dimsizes(lon2d(0,:))
===========================
Generally, when people see two dimensional latitude & longitude arrays (
cell_lat[*][*] and cell_lon[*][*] ), the grid structure is *'almost*
*always*' curvilinear. However, I noted that the file is a *L4* file (
*SMAP_L4*). NASA Level-4 files are '*almost always*' on a 'nice' grid.
I used an undocumented and unsupported function of mine to test if the grid
is a rectilinear grid despite the two-dimensional latitude & longitude
arrays. The function returns *True* if it is rectilinear and *False*
otherwise.
%> ncl tst.smap_rectilinear.ncl
The grid is rectilinear. Hence, you can use the approach you originally
used. (It did need a few improvements :-) )
%> ncl smap_regional.ncl_YiLu
Yes ... there are a fe locations over the water but if you use a higher
resolution map that will not be the case.
Good luck
On Thu, Dec 14, 2017 at 9:21 AM, Mary Haley <haley at ucar.edu> wrote:
> Dear Yi Lu,
>
> You are trying to extract the region from your HDF5 data by using
> coordinate subscripting.
>
> Coordinate subscripting can only be done on rectilinear data, which is
> data represented by one-dimensional lat/lon arrays that are the same length
> as their corresponding dimension.
>
> Your data is likely curvilinear, which means your data is represented by
> two-dimensional lat/lon arrays. I say this because in your code it looks
> like you are extracting 2D lat/lon arrays:
>
> lat2d = f->cell_lat
> lon2d = f->cell_lon
> nSmapLat = dimsizes(lat2d(:,0))
> nSmapLon = dimsizes(lon2d(0,:))
>
> Given this information, you cannot use coordinate subscripting to
> subscript your data. Instead, you either need to use the function
> *getind_latlon2d* or *region_ind* to get the indexes of the area of
> interest. For example:
>
> lat_reg = (/minLatBoundary,maxLatBoundary/)
> lon_reg = (/minLonBoundary,maxLonBoundary/)
> ij = getind_latlon2d(lat2d,lon2d,lat_reg,lon_reg)
> sm_regional = sm(ij(0,0):ij(1,0),ij(0,1):ij(1,1))
>
> Before plotting, you need to subset your lat2d / lon2d arrays using the
> same indexing:
>
> res at sfXArray = lon2d(ij(0,0):ij(1,0),ij(0,1):ij(1,1))
> res at sfYArray = lat2d(ij(0,0):ij(1,0),ij(0,1):ij(1,1))
>
> Please see our "Subsetting / extracting data based on lat / lon values"
> example page:
>
> http://www.ncl.ucar.edu/Applications/latlon_subset.shtml
>
> and in particular, look at examples latlon_subset_2.ncl and
> latlon_subset_3.ncl, which show the difference between getind_latlon2d and
> region_ind.
>
> Also, to better understand the different types of data (rectilinear,
> curvilinear, unstructured) and how to plot them, see:
>
> http://www.ncl.ucar.edu/Applications/plot_data_on_map.shtml
>
> Good luck,
>
> --Mary
>
>
> On Wed, Dec 13, 2017 at 7:05 PM, 易路 <dg1225033 at smail.nju.edu.cn> wrote:
>
>> Hi, all
>> Sorry to disturb you for technical help.
>>
>> I am trying to extract the regional data from the soil product SMAP L4
>> which is stored in the format of HDF5. I wrote the ncl script taking
>> referecnce to the example listed on the web of
>> http://www.ncl.ucar.edu/Applications/HDF.shtml. But the extracted data
>> were not in the demond region. So would you please help me to find the
>> faults in my ncl script? The main part of this script is as follow, and
>> the detail information can be downloaded from the accessory.
>> ********main part of the script *********
>> nFiles = dimsizes(iFiles)
>> f = addfile(iFiles(0), "r")
>> lat2d = f->cell_lat
>> lon2d = f->cell_lon
>>
>> nSmapLat = dimsizes(lat2d(:,0))
>> nSmapLon = dimsizes(lon2d(0,:))
>> minSmapLat = min(lat2d)
>> maxSmapLat = max(lat2d)
>> minSmapLon = min(lon2d)
>> maxSmapLon = max(lon2d)
>>
>> lat=fspan(minSmapLat, maxSmapLat, nSmapLat)
>> lat!0="lat"
>> lat&lat=lat
>> lat at units="degrees_north"
>> lat at long_name="Latitude"
>> lon=fspan(minSmapLon,maxSmapLon, nSmapLon)
>> lon!0="lon"
>> lon&lon=lon
>> lon at units="degrees_east"
>> lon at long_name="Longitude"
>>
>> lat2d!0="lat"
>> lat2d!1="lon"
>> lat2d&lon=lon
>> lat2d&lat=lat
>>
>> lon2d!0="lat"
>> lon2d!1="lon"
>> lon2d&lon=lon
>> lon2d&lat=lat
>>
>> minLatBoundary = 25
>> maxLatBoundary = 35
>> minLonBoundary = 110
>> maxLonBoundary = 120
>>
>> sm = f->sm_rootzone
>> printVarSummary(sm)
>> sm!0="lat"
>> sm!1="lon"
>> sm&lon=lon
>> sm&lat=lat
>> printVarSummary(sm)
>>
>> sm_regional = sm({minLatBoundary:maxLatBoundary},{minLonBoundary:
>> maxLonBoundary})
>> ***********************************
>>
>> Thanks a lot for your precious attentions and time!
>>
>> Yi Lu
>>
>>
>>
>>
>>
>> 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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