[ncl-talk] Masking
Mary Haley
haley at ucar.edu
Wed Nov 8 09:30:26 MST 2017
Muhammad,
Something is not right with data2.
In order to correctly mask curvilinear data, your lat/lon arrays must be
the same size as your data. If you look at the output from data2:
Variable: data2
Type: float
Total Size: 108360 bytes
27090 values
Number of Dimensions: 2
Dimensions and sizes: [y | 129] x [x | 210]
Coordinates:
Number Of Attributes: 9
lon2d : <ARRAY of 210 elements>
lat2d : <ARRAY of 210 elements>
stagger :
description : TEMP at 2 M
The data2 variable is 129 x 210, but the lat2d and lon2d are each 1D arrays
of length 210. lat2d and lon2d should be 2D arrays that are the same size
as data2.
However, and this is important, attaching lat2d and lon2d attributes to the
data variable is an NCL specific thing for plotting, regridding, and
masking, and should NOT be used when writing new data to a file. This is
needlessly expensive, because you likely already have the lat, lon arrays
written as separate variables on the file.
You can look at your original WRF output file to see how curvilinear data
is generally represented on a NetCDF file. Here's an example:
float T2 ( Time, south_north, west_east )
FieldType : 104
MemoryOrder : XY
description : TEMP at 2 M
units : K
stagger :
coordinates : XLONG XLAT XTIME
Note the "coordinates" attribute attached T2. This is what tells you that
the lat/lon arrays associated with T2 are called "XLONG" and "XLAT" on the
file, which is what I used earlier to get the lat/lon for masking.
The data2 variable longer has this coordinates attribute, so either NCO
didn't do something correctly, or this variable was modified in some way.
Please double-check that you are using NCO correctly, and don't write those
lat2d / lon2d attributes. Also make sure that the coordinates attribute is
included, and that you have the correct XLAT and XLONG variables written to
the file. Once you do this, you can then mask your new data in the exact
same way that you did for the original T2 variable.
--Mary
On Wed, Nov 8, 2017 at 12:35 AM, Muhammad Omer Mughal <
m.mughal1 at postgrad.curtin.edu.au> wrote:
> Hi Mary
>
>
> Thank you for the reply. The adjustment works perfectly to mask the data.
> I have another question related to this. When I use the wrfoutput file and
> use the commands lat2d I get this output
>
>
> Variable: data3
>
> Type: float
>
> Total Size: 108360 bytes
>
> 27090 values
>
> Number of Dimensions: 2
>
> Dimensions and sizes: [south_north | 129] x [west_east | 210]
>
> Coordinates:
>
> Number Of Attributes: 8
>
> lon2d : <ARRAY of 27090 elements>
>
> lat2d : <ARRAY of 27090 elements>
>
> coordinates : XLONG XLAT XTIME
>
> stagger :
>
> units : K
>
> description : TEMP at 2 M
>
> MemoryOrder : XY
>
> FieldType : 104
>
>
>
> When I use this to a sliced file from nco which has changed the attributes
> of the file I get the following output.
>
>
> Variable: data2
>
> Type: float
>
> Total Size: 108360 bytes
>
> 27090 values
>
> Number of Dimensions: 2
>
> Dimensions and sizes: [y | 129] x [x | 210]
>
> Coordinates:
>
> Number Of Attributes: 9
>
> lon2d : <ARRAY of 210 elements>
>
> lat2d : <ARRAY of 210 elements>
>
> stagger :
>
> description : TEMP at 2 M
>
> MemoryOrder : XY
>
> FieldType : 104
>
> coordinates : XLONG XLAT
>
> units : K
>
> time : 40320
>
> Also when I use the sliced file to mask the data I get the error
>
> (0) shapefile_mask_data:Error: not a valid rectilinear,curvilinear, or
> unstructured grid.
>
>
> I will appreciate your help
> Muhammad Omer Mughal
> MSc BSc Mechanical Engineering
> PhD Research Scholar
> Remote Sensing and Satellite Research Group
> Department of Imaging and Applied Physics
> Curtin University
>
> Curtin University
> Tel | +61 8 9266 7962
> Fax | +61 8 9266 2377
> Mobile | 0470 237 525
>
> Email | m.mughal1 at postgrad.curtin.edu.au <m.lynch at curtin.edu.au>
> Web | http://curtin.edu.au
>
> Curtin University is a trademark of Curtin University of Technology.
> CRICOS Provider Code 00301J (WA), 02637B (NSW)
>
>
> ------------------------------
> *From:* Mary Haley <haley at ucar.edu>
> *Sent:* Wednesday, 8 November 2017 12:42:12 AM
> *To:* Muhammad Omer Mughal
> *Cc:* ncl-talk at ucar.edu
> *Subject:* Re: [ncl-talk] Masking
>
> Muhammad,
>
> It looks like you are trying to use a rectilinear lat/lon grid for masking
> rather than the original lat/lon data associated with your "T2" variable.
>
> If your file is indeed a WRF output file, then you should use the
> XLAT/XLONG variables on the file, rather than trying to create your own
> lat/lon arrays.
>
> Your code would look something like this:
>
> nt = 0
> data
>
> = wrf_user_getvar(a, "T2",
>
> nt)
> data at lat2d = wrf_user_getvar(a, "lat", nt)
> data at lon2d = wrf_user_getvar(a,
>
> "lon",
>
> nt)
> data at _FillValue = -9999
>
> opt = True
> opt at debug = True
> data_mask = shapefile_mask_data(data,"Shapefile/malay.shp",opt)
>
>
> For an example that masks a WRF output file, see example
> shapefile_14_mask.ncl
>
> at:
>
> http://www.ncl.ucar.edu/Applications/shapefiles.shtml#ex14
>
> Note that this example is specifying "Ohio" as the specific area in the
> shapefile to mask against, but if you simply want to use the whole
> shapefile, then you do not need to set "shape_var" or "shape_names" as this
> script is doing.
>
> --Mary
>
> On Tue, Nov 7, 2017 at 6:48 AM, Muhammad Omer Mughal <
> m.mughal1 at postgrad.curtin.edu.au> wrote:
>
> Hi
>
> I am using a WRF output file and I did the following changes "ONLY" to the
> code[ https://www.ncl.ucar.edu/Applications/Scripts/mask_9.ncl] . I want
> to mask the temperature in Malaysia using the shape file malay.shp. Can
> you kindly tell me what else do I need to change as currently I am not
> able to see the data masked within Malaysia. I will be grateful for your
> help
>
>
> load "$NCARG_ROOT/lib/ncarg/nclscripts/wrf/WRFUserARW.ncl"
>
> begin
> MASK_INSIDE = True
>
> a = addfile("./UTC_0.nc","r")
> lat=a->XLAT
> lon=a->XLONG
>
> minlat=min(lat)
> maxlat=max(lat)
> minlon=min(lon)
> maxlon=max(lon)
>
> nlat=129
> nlon=210
>
> lat1d = fspan(minlat,maxlat,nlat)
> lon1d = fspan(minlon,maxlon,nlon)
>
> data = wrf_user_getvar(a, "T2", 0)
> data at _FillValue = -9999
>
>
>
> lat1d = fspan(minlat,maxlat,nlat)
> lon1d = fspan(minlon,maxlon,nlon)
> lat1d at units = "degrees_north"
> lon1d at units = "degrees_east"
>
> ;---Attach lat/lon coordinate array information.
> data!0 = "lat"
> data!1 = "lon"
> data&lat = lat1d
> data&lon = lon1d
>
>
>
> f = addfile("Shapefile/malay.shp", "r")
> mrb_lon = f->x
> mrb_lat = f->y
> nmrb = dimsizes(mrb_lon)
>
> min_mrb_lat = min(mrb_lat)
> max_mrb_lat = max(mrb_lat)
> min_mrb_lon = min(mrb_lon)
> max_mrb_lon = max(mrb_lon)
>
>
> www.ncl.ucar.edu
> <https://www.ncl.ucar.edu/Applications/Scripts/mask_9.ncl>
> www.ncl.ucar.edu
> ;***** ; mask_9.ncl ; ; Concepts illustrated: ; - Drawing the Mississippi
> River Basin using data from a shapefile ; - Masking a data array based on a
> geographical ...
>
>
> www.ncl.ucar.edu
> <https://www.ncl.ucar.edu/Applications/Scripts/mask_9.ncl>
> www.ncl.ucar.edu
> ;***** ; mask_9.ncl ; ; Concepts illustrated: ; - Drawing the Mississippi
> River Basin using data from a shapefile ; - Masking a data array based on a
> geographical ...
>
>
>
> Muhammad Omer Mughal
> MSc BSc Mechanical Engineering
> PhD Research Scholar
> Remote Sensing and Satellite Research Group
> Department of Imaging and Applied Physics
> Curtin University
>
> Curtin University
> Tel | +61 8 9266 7962
> Fax | +61 8 9266 2377
> Mobile | 0470 237 525
>
> Email | m.mughal1 at postgrad.curtin.edu.au <m.lynch at curtin.edu.au>
> Web | http://curtin.edu.au
>
> Curtin University is a trademark of Curtin University of Technology.
> CRICOS Provider Code 00301J (WA), 02637B (NSW)
>
>
>
> _______________________________________________
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