Re: Fwd: Wind barb spacing

I imagine your "trick" can work, but it seems like a bit of overkill in
terms of the processing required for the problem you posed initially. But
then again I do not know what your ultimate goal is.
 -dave


On Wed, Jul 23, 2014 at 3:43 PM, Rabah Hachelaf <hachelaf@sca.uqam.ca>
wrote:

> 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_re=
map_Wrap.shtml>*
> to transform the native grid (720X361) to a new grid regarding my distanc=
e
> 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 o=
f
>> (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 arra=
ys.
>> 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
>> do what you want. If you want to run this script you can download the da=
ta
>> 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 s=
hould
>>> be 0.125
>>> and when testing this i get a kind of random spacing (please see
>>> attached 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 arra=
y
>>> i50 = ind(x1D.lt.1000.) ; all indices x1D >=
 50
>>> x1D(i50) = -30 ; set all array synta=
x
>>> uu = onedtond(x1D, dimsizes(uu)); return to the origina=
l
>>> 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 arra=
y
>>> i50 = ind(x1D.lt.1000.) ; all indices x1D >=
 50
>>> x1D(i50) = -30 ; set all array synt=
ax
>>> vv = onedtond(x1D, dimsizes(vv)); return to the origina=
l
>>> 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 fil=
e
>>> gsn_define_colormap(wks,"gui_default")
>>>
>>> setvalues wks
>>> "wkBackgroundColor" : (/1.,1.,1./)
>>> end setvalues
>>>
>>>
>>> res = True ; plot mods desire=
d
>>> 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 barb=
s
>>> res@vcRefMagnitudeF = 1 ; make vectors large=
r
>>> 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
>>> ____
>>> ( )
>>> ( )
>>> (___ __)
>>> /////////
>>>
>>>
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> ncl-talk mailing list
>>> List instructions, subscriber options, unsubscribe:
>>> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>>>
>>>
>>
>
>
> --
> ------------------------------
> Cordialement,
> Best regards,
> Rabah Hachelaf
>

Received on Thu Jul 24 01:06:11 2014