[ncl-talk] how to add horizontal constant lines to a plot

[Rick Brownrigg]

Hi Anahita,

Just to follow up on this, my colleague Mary has added some examples of how
to draw reference lines, which are much easier and cleaner than the code I
suggested. Check out examples 36/36_vref  at:

http://www.ncl.ucar.edu/Applications/xy.shtml#ex36

Thanks Mary!

Rick


On Thu, Mar 30, 2017 at 7:44 AM, Rick Brownrigg <brownrig at ucar.edu> wrote:

>
> HI,
>
> One way would be to use gsn_add_polyline():
>
>     http://ncl.ucar.edu/Document/Graphics/Interfaces/gsn_add_
> polyline.shtml
>
> In short after each plot, you'd set up the line resources the way you
> want, and call this function 3 times for each plot for each of the three
> altitudes.  Note that you need to assign the results returned by the
> function to a unique variable, as the lines (nor the plots) aren't actually
> drawn until the call to gsn_panel.  So, for the first plot, something like:
>
>    ; these 3 lines done once...
>    lines = new((/12/), graphic)   ; variable to hold the 12 lines
>    lnres = True
>    lnnum = 0
>
>    plot(0) = gsn_csm_xy(......)
>    lnres at gsLineColor = "red"
>    lnres at gsLineDashPattern = ...
>    lines(lnnum) = gsn_add_polyline(wks, plot(0), (/res at trXMinF,
> res at trXMaxF/), (/1., 1./), lnres)
>    lnnum = lnnum + 1
>
>    lnres at gsLineColor = "blue
>    lnres at gsLineDashPattern = ...
>    lines(lnnum) = gsn_add_polyline(wks, plot(0), (/res at trXMinF,
> res at trXMaxF/), (/2., 2./), lnres)
>    lnnum = lnnum + 1
>
>    lnres at gsLineColor = "green"
>    lnres at gsLineDashPattern = ...
>    lines(lnnum) = gsn_add_polyline(wks, plot(0), (/res at trXMinF,
> res at trXMaxF/), (/3., 3./), lnres)
>    lnnum = lnnum + 1
>
> And so on. This is a bit tedious, and there are other ways to structure
> this, eg, you could draw all the plots, then add the lines looping over the
> plots, etc.  I'd probably turn the line drawing part into a function,
> passing in the colors, patterns, wks, and plot number, returning the line
> result.
>
> Hope that helps...
> Rick
>
> On Wed, Mar 29, 2017 at 10:17 PM, Anahita Amiri Farahani <aamir003 at ucr.edu
> > wrote:
>
>> Hello all,
>>
>> I want to add three horizontal constant lines (solid and dashed) at
>> different altitudes (1,2, and 3 km) with different colors to my plot but I
>> don't know how to do it. I have attached the figure and the code.
>>
>>
>>
>>
>>  wks = gsn_open_wks("eps","vertical_whole")
>> ; gsn_define_colormap(wks,"gui_default")
>>  plot = new(4,graphic)
>> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
>>   res                     = True               ; plot mods desired
>> res at gsnFrame        = False   ; don't draw yet
>>  res at gsnDraw         = False   ; don't advance frame yet
>>
>> res at tiXAxisString = "Dust extinction coefficient"  ; xaxis string
>>   res at tiYAxisString = "Altitude (km)"                  ; yaxis string
>> ;res at trYReverse        = True                       ; reverse Y-axis
>>
>>   res at trYMinF     = -1 ; set minimum Y-axis value
>>   res at trYMaxF     =  10 ; set maximum Y-axis value
>>   res at trXMinF     = 0        ; set minimum X-axis value
>>   res at trXMaxF     = 0.06       ; set maximum X-axis value
>>
>>
>> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
>>
>> res at gsnLeftString       = "Winter"         ; change left string
>> plot(0) = gsn_csm_xy(wks,extinct_winter_avg2,alt,res)
>> res at gsnLeftString       = "Spring"         ; change left string
>> plot(1) = gsn_csm_xy(wks,extinct_spring_avg2,alt,res)
>> res at gsnLeftString       = "Summer"         ; change left string
>> plot(2) = gsn_csm_xy(wks,extinct_summer_avg2,alt,res)
>> res at gsnLeftString       = "Fall"         ; change left string
>> plot(3) = gsn_csm_xy(wks,extinct_fall_avg2,alt,res)
>> ;************************************************
>> ; create panel
>> ;************************************************
>> resP                  = True                    ; modify the panel plot
>>
>>  resP at gsnPanelFigureStrings = (/"a)","b)","c)","d)"/)      ; add strings
>> to panel
>>  gsn_panel(wks,plot,(/2,2/),resP)
>>
>>
>> delete(plot)
>> delete(res)
>> delete(resP)
>> delete(wks)
>>
>>
>>
>>
>> Thanks,
>> Ana
>>
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