[ncl-talk] Masking

Thu Nov 9 06:39:03 MST 2017

Hi Marry

Thank you again for the reply. I found the problem after I used  CDO the time dimension stripped out from the data. In order to correct this problem I use the following
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)
  lat1d at units = "degrees_north"
  lon1d at units = "degrees_east"
  tc2a = wrf_user_getvar(a, "T2",0)
  tc2a at _FillValue = -9999

  tc2a!0      = "lat"
  tc2a!1      = "lon"
  tc2a&lat    = lat1d
  tc2a&lon    = lon1d
  tc2a_mask = shapefile_mask_data(tc2a,"/data/muhdomer/NSCC/scratch/Shapefiles/SGP_adm0.shp",opt)

Is there a way to get all variables masked using a shapefile_mask_data command ?

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<mailto:m.lynch at curtin.edu.au>
Web | http://curtin.edu.au<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: Thursday, 9 November 2017 12:30:26 AM
To: Muhammad Omer Mughal
Cc: ncl-talk at ucar.edu
Subject: Re: [ncl-talk] Masking

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<mailto: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<mailto:m.lynch at curtin.edu.au>
Web | http://curtin.edu.au<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<mailto:haley at ucar.edu>>
Sent: Wednesday, 8 November 2017 12:42:12 AM
To: Muhammad Omer Mughal
Cc: ncl-talk at ucar.edu<mailto: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<mailto: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<http://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<mailto:m.lynch at curtin.edu.au>
Web | http://curtin.edu.au<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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