[ncl-talk] Printing regression formula on plot

[Adam Phillips]

Hi Jason,
gsn_add_text
<http://www.ncl.ucar.edu/Document/Graphics/Interfaces/gsn_add_text.shtml>
is a function, so you need to pass the returned output to a variable.
Assuming a value of 70 is within the x-axis range of the plot, and 5.6 is
within the y-axis range, you should be good to go with something like this:
dum = gsn_add_text(wks,plt,text, 70, 5.6,txres)
Hope that helps!
Adam

On Fri, Oct 23, 2020 at 1:20 PM Herb, Jason via ncl-talk <
ncl-talk at mailman.ucar.edu> wrote:

> Hello all,
>
>    I am attempting to print the linear regression equation mX+b on my XY
> scatter plots. Unfortunatly, I have not had much luck in getting it to
> plot. Code script is below. Any suggestions?
>
> Thankyou
>
>
> ;This will create scatterplots of Modis derived PM2.5 data and surface
> measured PM2.5 data.
>
> begin
> f =  "QNC-XY.out"
> data = asciiread(f,(/5856,2/),"float")
> x = data(:,1)
> ; x = new((/2,366/),float)
>         x at _FillValue=integertoshort(-999)
>         x=where(x.lt.0,x at _FillValue,x)
> x at long_name = "PSP PM25"
> ; x(0,:) = data(:,4)
>         y = data(:,0)
> y at long_name = "Modis Derived PM25"
>         y at _FillValue=integertoshort(-999)
>         y=where(y.lt.0,y at _FillValue,y)
>
> ;************************************************
> ; calculate the regression coefficient (slope)
> ;************************************************
>    rcl    = regline(x, y)          ; slope
>    rcl at units = "MODIS/PSP"
>    print(rcl)
>
>    rcl_anova = regline_stats(x,y) ; linear regression: ANOVA
>    print(rcl_anova)
>
> ;************************************************
> ; create an array to hold both the original data
> ; and the calculated regression line
> ;     ---------
> ;     y = mx+b
> ;     m is the slope:       rc      returned from regline
> ;     b is the y intercept: rc at yave attribute of rc returned from regline
> ;************************************************
> ;   pltarry  := new ( (/2,366/), typeof(x), x at _FillValue)
>    pltarry  := new ( (/2,5856/), typeof(x), x at _FillValue)
> ;************************************************************
>    print(sprintf("%4.0f", x)+"  "+sprintf("%4.0f", y))
>
>    pltarry(0,:) = y                                 ; use markers
> ;   pltarry(1,:) = rcl*x + rcl at yintercept              ; use solid line
>    pltarry(1,:) = rcl*(x-rcl at xave) + rcl at yave ; y =m*x + B
>
> ;************************************************
> ; Plotting parameters
> ;************************************************
>         plot = new (1, "graphic")
>   wks  = gsn_open_wks("png","scatter_regress")             ; send graphics
> to PNG file
>
>   resP                     = True                ; modify the panel plot
>   resP at gsnMaximize         = True                ; maximize plot in frame
>   resP at gsnPanelMainString  = "Modis vs PSP"  ; title
>   resP at gsnPanelRowSpec     = True                   ; tell panel what
> order to plot
> ;  gsn_panel(wks,plot,(/2,1/),resP)
>
>
> ;  wks  = gsn_open_wks("png","scatter_regress")             ; send
> graphics to PNG file
>   res = True
>   res at gsnDraw = False
>   res at gsnFrame    = False
>   res at xyMarkLineModes     = (/"Markers","Lines"/)  ; choose which have
> markers
>    res at xyMarkers           = 16                     ; choose type of
> marker
>    res at xyMarkerColor       = "red"                  ; Marker color
>    res at xyMarkerSizeF       = 0.005                  ; Marker size
> (default 0.01)
>    res at xyDashPatterns      = 1                      ; solid line
>    res at xyLineThicknesses   = (/1,2/)                ; set second line to 2
>    res at tmYLFormat          = "f"                    ; not necessary but
> nicer labels
>
> ;   res at tiMainString        = "Modis vs PSP"  ; title
> ;    plt  = gsn_csm_xy (wks,x,pltarry,res)           ; create plot
> ;   plt  = gsn_csm_xy (wks,x,data,res)           ; create plot
>     res  = True
>   txres = True                                 ; label BW line
>   txres at txFontHeightF = 0.0175                 ; font height
>   txres at txJust        = "CenterCenter"         ; Set lable location
>
>   if (rcl_anova at b(0).gt.0) then
>       text  = "AOD_PM2.5 = "+ sprintf("%5.3f", rcl_anova at b(1))+"*PM25  +
> "+sprintf("%5.3f", abs(rcl_anova at b(0)))
>   else
>       text  = "AOD_PM2.5 = "+ sprintf("%5.3f", rcl_anova at b(1))+"*PM25  -
> "+sprintf("%5.3f", abs(rcl_anova at b(0)))
>   end if
>   plt  = gsn_csm_xy (wks,x,pltarry,res)           ; create plot
>   gsn_add_text(wks,plt,text, 70, 5.6,txres)
>   draw(plt)
>   frame(wks)
>
>
>
>
>
> ;  res at gsnMaximize       = True                     ; maximize plot
> ;  res at tiMainString      = "Scatter Plot"           ; add title
> ;  res at xyMarkLineMode    = "Markers"                ; choose to use
> markers
> ;  res at xyMarkers         =  16                      ; choose type of
> marker
> ;  res at xyMarkerColor     = "NavyBlue"               ; Marker color
> ;  res at xyMarkerSizeF     = 0.01                     ; Marker size
> (default 0.01)
> ;
> ; plot  = gsn_xy (wks,x,y,res)        ; create plot
> end
>
>
> _______________________________________________
> ncl-talk mailing list
> ncl-talk at mailman.ucar.edu
> List instructions, subscriber options, unsubscribe:
> https://mailman.ucar.edu/mailman/listinfo/ncl-talk



-- 
Adam Phillips
Associate Scientist,  Climate and Global Dynamics Laboratory, NCAR
www.cgd.ucar.edu/staff/asphilli/   303-497-1726

<http://www.cgd.ucar.edu/staff/asphilli>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mailman.ucar.edu/pipermail/ncl-talk/attachments/20201023/cc535b5b/attachment.html>