[ncl-talk] Contour Shape gets distorted for gsn_csm_contour_map plot
Dave Allured - NOAA Affiliate
dave.allured at noaa.gov
Fri Jan 4 13:32:22 MST 2019
Mansur,
Thanks for explaining the reason for recalculating the lat/lon
coordinates. I misunderstood your scenario.
I notice that your lat/lon calculations assume that the coordinates in each
data frame are equally spaced and independent between latitudes and
longitudes. In other words, you are assuming 1-dimensional coordinates.
You might want to check how the model really locates the output grid
points, and ensure your calculations match. Some models place their output
points on a map projection such that lats and lons vary independently for
every grid point. This is so-called 2-dimensional grid points.
Your corner points might be a clue. Corner points for 1-D coordinates are
often given as four numbers, min/max lat and lon. Corner points for 2-D
coordinates are usually given as four coordinate pairs, i.e. eight numbers.
In a similar situation (Daymet), I found it most reliable to obtain master
coordinate grids from the original data supplier, and use the provided X
and Y indices to obtain subset coordinate grids for each data tile. The
entire business of recalculation was pleasantly avoided. This might be
valid in your case, if your data frames are known to be proper subsets of a
master grid.
--Dave
On Thu, Jan 3, 2019 at 1:01 PM Mansur Ali Jisan <jisan.mansur at gmail.com>
wrote:
> Thank you for the replies and suggestions. I think the problem is with the
> output data frame. It's an output from parametric wind model with moving
> nest which gives only the lat-long for four corner points of the grid as a
> separate text file. I suspect there's something wrong with the calculation
> of those corner points. Thank you again!
>
> Regards,
> Mansur
>
> On Wed, Jan 2, 2019 at 5:04 PM Dave Allured - NOAA Affiliate <
> dave.allured at noaa.gov> wrote:
>
>> 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
>>
>
> --
> *Mansur Ali Jisan*
> Ph.D. Student
> URI Graduate School of Oceanography, RI 02882
> <hasancee at iut-dhaka.edu>
>
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