On 03/14/2014 07:05 PM, al Vel wrote:
Hi,
I was very clear in the mail that i want to create a four edged
Barycentric diagram like Ternary plot (like the rhombus in the piper
diagram (http://en.wikipedia.org/wiki/Piper_diagram)). The idea is to
graphically depicts the ratios of the four variables as positions in an
rhombus/diamond shape. The more the value, then the point will be
towards that edge. In a four edged plot, the proportions of the four
variables /a/, /b/, c, d must sum to some constant, /K/. Usually, this
constant is represented as 1.
The code is simple for 3-edged ternary plot:
>grid.polygon(c(0, 0.5, 1), c(0, sqrt(3)/2, 0), gp = gpar(col = "black"))
>xp <- proportionvalueofB + proportionvalueofC / 2
>yp <- proportionvalueofC * sqrt(3)/2
> grid.points(xp, yp, pch = 1, size=size, default.units = "snpc")
(example if a=10,b=20,c=40; then proportionvalueofB=20/70)
The second two line in the above code converts the proportion value into
a cartesian co-oridinate to plot. This is for the triangle. The question
is how do i convert the proportions of 4 values into a cartesian
co-ordinate in a rhombus or a diamond.
Best regards,
Alaguraj.V
Hi Alaguraj,
Okay, the A, B, C, and D represent distances along the sides of a
rhombus. The important thing is that you have answered your own
question. The Wikipedia page above has the matrix transformation to
solve your problem. Also have a look at this site:
http://water.usgs.gov/nrp/gwsoftware/GW_Chart/GW_Chart.html
where there is free software to draw Piper diagrams. Unfortunately, it
is written in Pascal so that I can't easily translate it into R. There
is an R package "hydrogeo" that may have a Piper diagram function in it.
If you manage to sort this out, please let me know as I had a Piper
diagram function that was contributed to the plotrix package but didn't
work.
Jim
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