[ncl-talk] Conformal projection

[Carlos Peralta]

Thanks very much!
Best wishes
Carlos

On Thu, Sep 17, 2020, 00:40 Dennis Shea <shea at ucar.edu> wrote:

> To examine the contents of the GRIB file:
>
> %> *ncl_filedump
> <https://www.ncl.ucar.edu/Document/Tools/ncl_filedump.shtml> *CW_Tskin.grib
> | less
>
> This provides an '*ncdump -h*' style look of the grib file [attachment:
> *CW_Tskin.dump* ].It also provides value added variables: grid point
> latitude and longitude and map information.
>
> Using the information contained within the grib file;
>
> %> ncl *CW_CARLOS.ncl*
>
> produced *CARLOS_CW_Tskin.grib.png*
>
> Cell mode was used because it was faster. [ I do not know why! ]
>
> Good Luck
>
>
>
>
> On Tue, Sep 15, 2020 at 7:41 PM Rick Brownrigg via ncl-talk <
> ncl-talk at mailman.ucar.edu> wrote:
>
>> Hi Carlos,
>>
>> The map is *probably* OK, I don't know for certain. Looking at planar
>> maps near the poles is weird, and I've seen what you describe with E/W
>> longitudes labeling all sides. But look at greenland on a globe and it kind
>> of makes sense. I think if you set the resource "mpGridAndLimbOn=True", the
>> lines of longitude will make a bit more sense*.*
>>
>> Rick
>>
>>
>> On Tue, Sep 15, 2020 at 12:53 PM Carlos Peralta via ncl-talk <
>> ncl-talk at mailman.ucar.edu> wrote:
>>
>>> Hello,
>>>
>>> I am following example 3 here:
>>>
>>> https://www.ncl.ucar.edu/Applications/Scripts/lcnative_3.ncl
>>>
>>> to plot a grb file where I am not sure of what the appropriate
>>> parallels are.
>>>
>>> I get the figure below, which seems correct, but not sure
>>> why I see the axes displayed with "W" and "E" in both the vertical
>>> and horizontal.
>>>
>>> thanks for any help.
>>>
>>>
>>> My code is below
>>>
>>> ;------------------------------------------------
>>> ; lcnative_3.ncl
>>> ;------------------------------------------------
>>> ;
>>> ; These files are loaded by default in NCL V6.2.0 and newer
>>> ; load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
>>> ; load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
>>>
>>> begin
>>>
>>> ;------------------------------------------------
>>> ; open file and read in data
>>> ;------------------------------------------------
>>>   gfile= "./CW_Tskin.grib"
>>>   f     = addfile (gfile, "r")
>>>   printVarSummary(f)
>>>   ;fili  = "ruc2.bgrb.20020418.i12.f00.grb"
>>>   ;f     = addfile (fili, "r")
>>>
>>>   ;vpt       = f->VPTMP_252_HYBL
>>>   vpt       = f->TMP_GDS3_HTGL(g3_x_0|:,g3_y_1|:)
>>>   ;lat2d     = f->gridlat_252
>>>   ;lon2d     = f->gridlon_252
>>>    lat2d=f->g3_lat_0
>>>    lon2d=f->g3_lon_1
>>>
>>>
>>> ;------------------------------------------------
>>> ; create plot
>>> ;------------------------------------------------
>>>   wks = gsn_open_wks("png","lcnative")      ; send graphics to PNG file
>>>
>>>   res                   = True              ; plot mods desired
>>>   res at tiMainString      = "Native Lambert Conformal"
>>>   res at gsnAddCyclic = False
>>> ;------------------------------------------------
>>> ; lambert conformal projections are limited using
>>> ; the corners method rather than the latlon method
>>> ; seen for cylindrical equidistant projections
>>> ;------------------------------------------------
>>>   res at mpLimitMode       = "Corners"         ; choose range of map
>>>   res at mpLeftCornerLatF  = lat2d at corners(0)
>>>   res at mpLeftCornerLonF  = lon2d at corners(0)
>>>   res at mpRightCornerLatF = lat2d at corners(2)
>>>   res at mpRightCornerLonF = lon2d at corners(2)
>>> ;------------------------------------------------
>>> ; there are many instances when you may not know the
>>> ; appropriate parallels. Here is a method to find out...
>>> ; 1) as a first guess, start with the parellels in the
>>> ;    center of the grid.
>>> ; 2) look at the lines plotted on the map (see below).
>>> ;    you know the projection is correct when the red
>>> ;    and blue lines form a right angle between themselves
>>> ;    and the boundary.
>>> ; 3) iterate as necessary to get the closest solution.
>>> ;------------------------------------------------
>>>   res at mpProjection          = "LambertConformal"
>>>
>>>   res at mpLambertParallel1F = (max(lat2d)+min(lat2d))*0.5
>>>   res at mpLambertParallel2F = (max(lat2d)+min(lat2d))*0.5
>>>   res at mpLambertMeridianF  = (max(lon2d)+min(lon2d))*0.5
>>>
>>> ;------------------------------------------------
>>>   res at pmTickMarkDisplayMode = "Always"
>>>   res at mpFillOn              =  False           ; turn off map fill
>>>   res at mpOutlineDrawOrder    = "PostDraw"       ; draw continental
>>> outline last
>>>   res at mpOutlineBoundarySets = "GeophysicalAndUSStates" ; state
>>> boundaries
>>>
>>> ;------------------------------------------------
>>> ; usually, when data is placed onto a map, it is TRANSFORMED to the
>>> specified
>>> ; projection. Since this model is already on a native lambert conformal
>>> grid,
>>> ; we want to turn OFF the transformation.
>>> ;------------------------------------------------
>>>
>>>   res at tfDoNDCOverlay = True
>>> ; res at tfDoNDCOverlay = "NDCViewport"          ; NCL V6.5.0 or later
>>>
>>>
>>> ;------------------------------------------------
>>> ; set additional resources and create plot
>>> ;------------------------------------------------
>>>   res at cnFillOn              = True            ; color plot desired
>>>   res at cnLinesOn             = False           ; turn off contour lines
>>>   res at cnFillPalette         = "gui_default"   ; set color map
>>>   res at gsnFrame              = False           ; don't advance frame yet
>>>
>>>   ;plot = gsn_csm_contour_map(wks,vpt(9,:,:),res) ; draw plot
>>>   plot = gsn_csm_contour_map(wks,vpt(:,:),res) ; draw plot
>>>
>>> ;------------------------------------------------
>>> ; add lines that help determine correct projection
>>> ;------------------------------------------------
>>>   dims  = dimsizes(vpt)                       ; get dimension of grid
>>>   ;nlat  = dims(1)
>>>   ;nlon  = dims(2)
>>>   nlat  = dims(0)
>>>   nlon  = dims(1)
>>>
>>>   gres                  = True                ; polyline mods desired
>>>   gres at gsLineThicknessF = 3.0                 ; line thickness
>>>   gres at gsLineColor      = "Red"               ; line color
>>>   gsn_polyline (wks, plot, lon2d(nlat/2,:), lat2d(nlat/2,:), gres)
>>>
>>>   gres at gsLineColor      = "Blue"
>>>   gsn_polyline (wks, plot, lon2d(:,nlon/2), lat2d(:,nlon/2), gres)
>>>
>>>   gres at gsLineColor      = "Black"
>>>   gsn_polyline (wks, plot, lon2d(:,0)     , lat2d(:,0), gres)
>>>   gsn_polyline (wks, plot, lon2d(:,nlon-1), lat2d(:,nlon-1), gres)
>>>   gsn_polyline (wks, plot, lon2d(0,:)     , lat2d(0,:), gres)
>>>   gsn_polyline (wks, plot, lon2d(nlat-1,:), lat2d(nlat-1,:), gres)
>>>
>>>   frame(wks)
>>>
>>> end
>>>
>>>
>>>
>>>
>>> [image: image.png]
>>>
>>>
>>>
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