[ncl-talk] Contour Shape gets distorted for gsn_csm_contour_map plot
Dave Allured - NOAA Affiliate
dave.allured at noaa.gov
Wed Jan 2 15:04:22 MST 2019
Mansur,
1. I strongly advise against generating your own lat and lon coordinates
when valid coordinates are provided with the input data. Regeneration can
easily lead to blatant or subtle map registration errors, if there are any
mistakes.
2. Your script uses the cylindrical equidistant projection by default.
This will produce distortion everywhere except near the equator. To
minimize distortion elsewhere, please use a locally conformal map
projection. For minimal distortion in a small circular region of the
globe, I recommend Azimuthal Equidistant with the tangent point at the
center of the region. Lambert Conformal Conic is a good compromise
projection, commonly used, for larger mid-latitude regions that are wider
east to west, such as continental USA. There are other good choices for
small and medium regions.
https://www.ncl.ucar.edu/Document/Graphics/map_projections.shtml
--Dave
On Wed, Jan 2, 2019 at 11:23 AM Rick Brownrigg <brownrig at ucar.edu> wrote:
>
> Hi,
>
> Given the aspect ratio of the underlying data (range of -74.25...-70.17
in lon, 36...46.9 in lat), it seems like the plot produced via
gsn_csm_contour_map is about what one would expect ? I see you manually
assigned those geographic coordinates to the grid. Are those correct? Do
you have other reasons to believe the storm shape should be more circular,
rather than elongated?
>
> Not sure what to suggest here...
>
> Rick
>
>
> On Wed, Jan 2, 2019 at 10:46 AM Mansur Ali Jisan <jisan.mansur at gmail.com>
wrote:
>>
>> Dear NCL Community,
>>
>> I need help with contour map plot for a Hurricane wind field. At first,
I used gsn_csm_contour function for making the plot and the shape of the
storm looked correct. But when I tried to make a contour map plot using
gsn_csm_contour_map, the shape got distorted. I tried to solve this by
setting the res at mpShapeMode = "FreeAspect". While it improved the contour
plot but the map got stretched. Similarly, I set up the map projection to
cylindrical equidistant but still got the same result. I have added the
code and PrintVarSummary. Any suggestions will be very helpful.
>>
>> Wishing you a Happy New Year!
>>
>>
--------------------------------------------------------------------------------------------------------
>>
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
>> begin
>> ntim = 318
>> nlat = 1202
>> mlon = 1202
>>
>> f1 = addfile("bound_param_diag_var_rough.nc","r")
>> u = f1->um_bot ; 97 x 1202 x 1202
>> v = f1->vm_bot
>> ws = sqrt(u^2+v^2)
>>
>> lat = fspan(36.07092, 46.86241,nlat)
>> lon = fspan(-74.25677, -70.17657,mlon)
>>
>> lat!0= "lat" ; name dimension
>> lat at units = "degrees_north" ; associate units attribute
>> lat&lat = lat ; coordinate variable
>>
>> lon!0= "lon"
>> lon at units = "degrees_east"
>> lon&lon = lon
>>
>> u!0 = "time"
>> u!1 = "lat"
>> u!2 = "lon"
>> u&lat = lat
>> u&lon = lon
>> v!0 = "time"
>> v!1 = "lat"
>> v!2 = "lon"
>>
>> v&lat = lat
>> v&lon = lon
>>
>> ws!0 = "time"
>> ws!1 = "lat"
>> ws!2 = "lon"
>>
>> ws&lat = lat
>> ws&lon = lon
>>
>> printVarSummary(lat)
>> print("-----")
>> printVarSummary(lon)
>> print("-----")
>> printVarSummary(u)
>> print("-----")
>>
>> ws = mask(ws,ws.lt.4,False)
>> u = mask(u,u.lt.4,False)
>> v = mask(v,v.lt.4,False)
>>
>> wks = gsn_open_wks("png","gsn_csm_contour_map")
>> res = True
>> res at gsnDraw = False
>> res at gsnFrame = False
>> res at gsnAddCyclic = False
>> res at gsnMaximize = True
>> res at cnFillOn = True
>> res at cnLinesOn = False
>> res at cnFillMode = "AreaFill"
>> res at cnFillPalette = "matlab_jet"
>>
>> ; res at mpShapeMode = "FreeAspect"
>> ; res at vpWidthF = 0.6
>> ; res at vpHeightF = 0.5
>>
>> res at tmXBOn = True
>> res at tmYLOn = True
>> res at tiMainString = "gsn_csm_contour_map"
>> res at tmXBMode = "Explicit"
>> res at tmXBValues = (/-66, -67, -68, -69, -70, -71, -72, -73, -74,
-75, -76, -77/)
>> res at tmXBLabels =
(/"66W","67W","68W","69W","70W","71W","72W","73W","74W","75W","76W","77W"/)
>>
>> res at tmYLMode = "Explicit"
>> res at tmYLValues = (/34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45,
46, 47/)
>> res at tmYLLabels =
(/"34N","35N","36N","37N","38N","39N","40N","41N","42N","43N","44N","45N","46N","47N"/)
>>
>> res at cnLevelSelectionMode = "ManualLevels"
>> res at cnMinLevelValF = 10
>> res at cnMaxLevelValF = 80
>> res at cnLevelSpacingF = 2.5
>>
>> res at mpFillOn = False
>> res at mpGeophysicalLineThicknessF = 2.5
>> res at mpOutlineBoundarySets = "geophysicalandusstates"
>> res at mpDataBaseVersion = "MediumRes"
>> res at mpDataSetName = "Earth..4"
>> res at mpGeophysicalLineColor = "Black"
>>
>> res at mpLimitMode = "LatLon"
>> res at mpMinLatF = 36.0
>> res at mpMaxLatF = 46.0
>> res at mpMinLonF = -76.0
>> res at mpMaxLonF = -70.0
>>
>> plot = gsn_csm_contour_map(wks,ws(22,:,:),res)
>>
>> draw(plot)
>>
>> frame(wks)
>>
>> end
>>
>> Variable: lat
>> Type: float
>> Total Size: 4808 bytes
>> 1202 values
>> Number of Dimensions: 1
>> Dimensions and sizes: [lat | 1202]
>> Coordinates:
>> lat: [36.07092..46.86241]
>> Number Of Attributes: 1
>> units : degrees_north
>> (0) -----
>>
>> Variable: lon
>> Type: float
>> Total Size: 4808 bytes
>> 1202 values
>> Number of Dimensions: 1
>> Dimensions and sizes: [lon | 1202]
>> Coordinates:
>> lon: [-74.25677..-70.17657]
>> Number Of Attributes: 1
>> units : degrees_east
>> (0) -----
>>
>> Variable: u
>> Type: float
>> Total Size: 1837790688 bytes
>> 459447672 values
>> Number of Dimensions: 3
>> Dimensions and sizes: [time | 318] x [lat | 1202] x [lon | 1202]
>> Coordinates:
>> lat: [36.07091903686523..46.86241149902344]
>> lon: [-74.25676727294922..-70.17656707763672]
>> Number Of Attributes: 1
>> units :
>> (0) -----
>>
>> --
>> Mansur Ali Jisan
>> Ph.D. Student
>> URI Graduate School of Oceanography, RI 02882
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