Re: Fwd: Wind barb spacing

Hi David,

Thanks for your replay ,
I think i solved my problem by using a regridding my data , i used this
function *area_conserve_remap_Wrap
<https://www.ncl.ucar.edu/Document/Functions/Contributed/area_conserve_rema=
p_Wrap.shtml>*
to transform the native grid (720X361) to a new grid regarding my distance
requested for my case (8 X 5)
and it seems work.

What do you think about this trick.

Rabah


2014-07-23 17:26 GMT-04:00 David Brown <dbrown@ucar.edu>:

> Hi Rabah,
> The vcMinDistanceF resource is really designed to even out the spacing of
> (usually more dense) grids of vectors where the map projection leads to
> crowding in some areas of the plot.
>
> In your case, where you want to draw only a very sparse number of vectors=
,
> it would make more sense to use vector subscripting on the arrays.
> The NCL function that could help you is 'ind_nearest_coord'.
> I am attaching a modified version of the example barb_1.ncl that should d=
o
> what you want. If you want to run this script you can download the data
> file '83.nc' from the data link in the NCL example page.
>
>
>
>
> On Tue, Jul 22, 2014 at 5:38 PM, Rabah Hachelaf <hachelaf@sca.uqam.ca>
> wrote:
>
>>
>> Hi NCL users,
>>
>> I am using "vcMinDistanceF" to control wind barb spacing from GFS data.
>> according to my understanding when i want plot the whole world map
>>
>> -180 to 180 longitude is mapped to 0-1 in NDC space
>> and -90 to 90 latitude is mapped to 0-1 in NDC space
>>
>> if so and if i want to draw a wind barb each 45°, vcMinDistanceF sh=
ould
>> be 0.125
>> and when testing this i get a kind of random spacing (please see attache=
d
>> image)
>>
>> So is there any solution to control barb spacing according geographical
>> distance (in degrees).
>>
>> Thank you for help.
>> below is you find my ncl script used :
>>
>> ;************************************************
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
>> ;************************************************
>> begin
>>
>> ;************************************************
>> ; read in GRIB2 file
>> ;************************************************
>> a = addfile("gfs.t00z.pgrb2f00.grib2","r")
>> ;************************************************
>> ;;; get variables: temperature, longitude, latitude
>>
>> t2m = a->TMP_P0_2L108_GLL0(:,:)
>> lon = a->lon_0
>> lat = a->lat_0
>> uu= a->UGRD_P0_L6_GLL0
>> vv= a->VGRD_P0_L6_GLL0
>>
>>
>> if (any(uu.lt.1000.)) then
>> x1D = ndtooned (uu) ; convert to 1D array
>> i50 = ind(x1D.lt.1000.) ; all indices x1D > =
50
>> x1D(i50) = -30 ; set all array syntax
>> uu = onedtond(x1D, dimsizes(uu)); return to the original
>> array
>> delete (x1D) ; x1D no longer needed
>> delete (i50) ; i50 no longer needed
>> end if
>>
>> if (any(vv.lt.1000.)) then
>> x1D = ndtooned (vv) ; convert to 1D array
>> i50 = ind(x1D.lt.1000.) ; all indices x1D > =
50
>> x1D(i50) = -30 ; set all array synta=
x
>> vv = onedtond(x1D, dimsizes(vv)); return to the original
>> array
>> delete (x1D) ; x1D no longer needed
>> delete (i50) ; i50 no longer needed
>> end if
>>
>> ;
>>
>> ; create plot
>> ;************************************************
>> wks_type="png"
>>
>> wks_type@wkWidth = 1384
>> wks_type@wkHeight = 1384
>> wks_type@wkBackgroundOpacityF = 1.0
>>
>>
>> wks = gsn_open_wks(wks_type,"wind_barb") ; open a ncgm file
>> gsn_define_colormap(wks,"gui_default")
>>
>> setvalues wks
>> "wkBackgroundColor" : (/1.,1.,1./)
>> end setvalues
>>
>>
>> res = True ; plot mods desired
>> res@pmTickMarkDisplayMode = "Always"
>> res@mpProjection = "Mercator" ; choose projection
>> res@mpGridAndLimbOn = True ; turn on lat/lon lines
>> res@mpPerimOn = True ; turn off box around plot
>> res@mpGridLatSpacingF = 45. ; spacing for lat lines
>> res@mpGridLonSpacingF = 45. ; spacing for lon lines
>> res@mpFillOn = False
>> res@mpLimitMode = "LatLon"
>> res@mpMinLatF = 85.0
>> res@mpMaxLatF = -85.0
>> res@mpMinLonF = -180
>> res@mpMaxLonF = 180
>>
>> res@cnFillOn = False ; color plot desired
>> res@cnLineLabelsOn = False ; turn off contour lines
>>
>> res@vpXF = 0 ; make plot bigger
>> res@vpYF = 1
>> res@vpWidthF = 1
>> res@vpHeightF = 1
>>
>>
>> res@vcGlyphStyle = "WindBarb" ; select wind barbs
>> res@vcRefMagnitudeF = 1 ; make vectors larger
>> res@vcRefLengthF = 0.03 ; ref vec length
>> res@vcWindBarbLineThicknessF = 8.0 ;Thickness
>>
>>
>> res@vcWindBarbTickSpacingF = 0.125 ;
>>
>> res@vcMinDistanceF = 0.125 ; thin out windbarbs
>> res@vcMonoWindBarbColor = True
>> res@vcWindBarbColor = 1
>>
>> res@mpOutlineOn = True ; turn on map outline
>> plot1=gsn_csm_vector_map(wks,uu,vv,res)
>>
>>
>>
>> ------------------------------
>> Cordialement,
>> Best regards,
>> Rabah Hachelaf
>> ____
>> ( )
>> ( )
>> (___ __)
>> /////////
>>
>>
>>
>>
>>
>>
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>>
>>
>


--
------------------------------
Cordialement,
Best regards,
Rabah Hachelaf

Received on Wed Jul 23 09:43:40 2014