Re: [R] Soil texture triangle in R?

From: Sander Oom <slist_at_oomvanlieshout.net>
Date: Fri 27 May 2005 - 23:32:54 EST

Hi Jim,

This looks impressive! It gives me the 'background' graph. However, I'm not sure how I can use this function to plot my soil texture values! Can you explain?

I would like to be able to plot my soil texture samples in the same graph as the one your function plots.

Maybe I should try to figure out how to replicate your code inside a ternaryplot{vcd} call.

Cheers,

Sander.

Jim Lemon wrote:
> Sander Oom wrote:
>> Dear R users,
>>
>> has anybody made an attempt to create the soil texture triangle graph
>> in R? For an example see here:
>>
>> http://www.teachingkate.org/images/soiltria.gif
>>
>> I would like to get the lines in black and texture labels in gray to
>> allow for plotting my texture results on top.
>>
>> Any examples or suggestions are very welcome!
>>
> It's not too hard to write a plot function to do this, but I'm not sure
> whether this will be what you want. Anyway, try it out.
>
> Jim
>
> ------------------------------------------------------------------------
>
> soil.triangle<-function() {
> oldpar<-par(no.readonly=TRUE)
> plot(0:1,type="n",axes=FALSE,xlim=c(0,1.1),ylim=c(0,1),
> main="Soil Triangle",xlab="",ylab="")
> # first draw the triangle
> x1<-c(0,0,0.5)
> sin60<-sin(pi/3)
> x2<-c(1,0.5,1)
> y1<-c(0,0,sin60)
> y2<-c(0,sin60,0)
> segments(x1,y1,x2,y2)
> # now the bottom internal ticks
> x1<-seq(0.1,0.9,by=0.1)
> x2<-x1
> y1<-rep(0,9)
> y2<-rep(0.02,9)
> segments(x1,y1,x2,y2)
> text(x1,y1-0.03,as.character(rev(seq(10,90,by=10))))
> # now the left internal ticks
> y1<-x1*sin60
> x1<-x1*0.5
> x2<-x1+0.02*sin60
> y2<-y1-0.02*0.5
> segments(x1,y1,x2,y2)
> text(x1-0.03,y1+0.015,as.character(seq(10,90,by=10)))
> x1<-rev(x1+0.5-0.02*sin60)
> x2<-x1+0.02*sin60
> segments(x1,y2,x2,y1)
> text(x2+0.03,y1+0.015,as.character(rev(seq(10,90,by=10))))
> text(0.5,0.9,"100% clay")
> par(xpd=TRUE)
> text(-0.1,0,"100% sand")
> text(1.1,0,"100% loam")
> text(0.07,0.43,"percent clay")
> text(0.93,0.43,"percent silt")
> text(0.5,-0.1,"percent sand")
> # boundary of clay with extensions
> x1<-c(0.275,0.35,0.6)
> x2<-c(0.4,0.79,0.7)
> y1<-c(0.55*sin60,0.41*sin60,0.41*sin60)
> y2<-c(0.285*sin60,0.41*sin60,0.6*sin60)
> segments(x1,y1,x2,y2)
> text(0.5,0.57,"Clay")
> # lower bound of clay loam & silty divider
> x1<-c(0.4,0.68)
> x2<-c(0.86,0.6)
> y1<-c(0.285*sin60,0.285*sin60)
> y2<-c(0.285*sin60,0.41*sin60)
> segments(x1,y1,x2,y2)
> text(0.7,0.49*sin60,"Silty")
> text(0.7,0.44*sin60,"clay")
> text(0.73,0.37*sin60,"Silty clay")
> text(0.73,0.33*sin60,"loam")
> text(0.5,0.35*sin60,"Clay loam")
> x1<-c(0.185,0.1,0.37)
> x2<-c(0.36,0.37,0.4)
> y1<-c(0.37*sin60,0.2*sin60,0.2*sin60)
> y2<-c(0.37*sin60,0.2*sin60,0.285*sin60)
> segments(x1,y1,x2,y2)
> text(0.27,0.43*sin60,"Sandy")
> text(0.27,0.39*sin60,"clay")
> text(0.27,0.3*sin60,"Sandy clay")
> text(0.27,0.26*sin60,"loam")
> # sand corner
> x1<-c(0.05,0.075)
> x2<-c(0.12,0.3)
> y1<-c(0.1*sin60,0.15*sin60)
> y2<-c(0,0)
> segments(x1,y1,x2,y2)
> text(0.25,0.13*sin60,"Sandy loam")
> text(0.13,0.075*sin60,"Loamy")
> text(0.15,0.035*sin60,"sand")
> text(0.055,0.021,"Sand")
> x1<-c(0.37,0.42,0.5,0.8,0.86)
> x2<-c(0.42,0.54,0.65,0.86,0.94)
> y1<-c(0.2*sin60,0.08*sin60,0,0,0.12*sin60)
> y2<-c(0.08*sin60,0.08*sin60,0.285*sin60,0.12*sin60,0.12*sin60)
> segments(x1,y1,x2,y2)
> text(0.49,0.18*sin60,"Loam")
> text(0.72,0.15*sin60,"Silt loam")
> text(0.9,0.06*sin60,"Silt")
> par(oldpar)
> }



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