[ncl-talk] Adding a marker on a contouring map

[G.Monte at isac.cnr.it]

> What you did was right and I cannot see any obvious errors in your code.
> Usually if you get no errors it's because the marker get placed but
> somewhere where you don't expect, or maybe the marker size is too small,
> but that's not your case, 5 should be big enough.
>
> Can you share a minimal working version of your script and data?
> You could also try to change the bounds of your map projection to include
> all the globe and see where your marker is wandering around :-)
>
I changed the bounds to include all the globe and fixed two pairs of
latitude-longitude, but the markers didn't appear anywhere. I'm working
with GPM-DPR data of radar reflecitivity (h5); here are some code lines
relative to the graphics part, both for plotting the contour map and for
adding the markers:

begin
......
wks =
gsn_open_wks("png","./radar_reflectivity/near_surface/corrected_zfactor_map_marker")
res                      = True
res at gsnAddCyclic         = False
res at gsnMaximize          = True
res at cnFillOn             = True
res at cnFillMode           = "RasterFill"
res at cnFillPalette        = "BlueWhiteOrangeRed"
res at cnLinesOn            = False
res at cnLineLabelsOn       = False
res at mpFillOn             = True
res at cnLevelSelectionMode = "ManualLevels"
res at cnMinLevelValF       = min(z)
res at cnMaxLevelValF       = max(z)
res at cnLevelSpacingF      = 1.
res at cnMissingValFillColor = "transparent"

;-----------------------------------------------------------
; plot sub area; for faster plot only use desired sub-region
;-----------------------------------------------------------
minLat    =  -66
maxLat    =  66
minLon    =  -180
maxLon    =  180
res at mpMinLatF = minLat
res at mpMaxLatF = maxLat
res at mpMinLonF = minLon
res at mpMaxLonF = maxLon
;----------------------------------------------------
; extract indices of desired sub-region
;----------------------------------------------------
ji    = region_ind(latitude,longitude, minLat, maxLat, minLon, maxLon)
jStrt = ji(0)      ; scan start
jLast = ji(1)      ; scan last
iStrt = ji(2)      ; ray  start
iLast = ji(3)      ; ray  last
Z_region       = z(jStrt:jLast,iStrt:iLast)  ; [nscan x nray]
Z_region at lat2d = latitude(jStrt:jLast,iStrt:iLast)
Z_region at lon2d = longitude(jStrt:jLast,iStrt:iLast)
plot           = gsn_csm_contour_map(wks,Z_region,res)

polyres                   = True
polyres at gsMarkerIndex     = 16
polyres at gsMarkerSizeF     = 10.
polyres at gsFillColor       = "black"
polyres at tfPolyDrawOrder   = "Draw"
lat  = (/45.43, 5./)
lon  = (/12.12, 5./)
dum  =  gsn_add_polymarker(wks,plot,lon,lat,polyres)
draw(plot)
end

Giulio Monte
















> Il mer 20 giu 2018, 11:54 <G.Monte at isac.cnr.it> ha scritto:
>
>> Dear all,
>> I would like to add a marker for a given latitude-longitude
>> (45.43°N,12.12°E) on a contouring map in NCL 6.4.0. For the plot, I used
>> gsn_csm_contour_map function and I need only a single marker to add in.
>> I
>> tried the following commands:
>>
>> polyres                   = True
>> polyres at gsMarkerIndex     = 16
>> polyres at gsMarkerSizeF     = 5.
>> plot =  gsn_csm_contour_map(wks,Z_region,res)
>> dum  =  gsn_add_polymarker(wks,plot,12.12,45.43,polyres)
>> draw(plot)
>>
>> and no error messages appeared, but marker was not added on the map
>> anyway.
>> I do not understand the reason; maybe, I think that gsn_add_polymarker
>> function would be suited only for several markers. Are there existing
>> other functions to add a single marker on a NCL contouring map?
>>
>> Thanks,
>> Giulio Monte
>>
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>