Pedal chart script

[wageningen]

A remark, perhaps useful. I got a request from a colleague of ISRIC to create in R a pedal chart, also called rose chart, like this (the data are fictional):
.
As I couldn't find a function or package, I wrote something myself. It will probably need adjustments (for example, I made it static: it can only show six leaves), but for inspiration, this is the code:

## script for plotting six roses in polar plot - "Pedal chart" 
# Luc Steinbuch, 22/10/2016

#You need to install this package one time: 
install.packages('plotrix')

# and load it..
require(plotrix)

# mathematical background: 
# browseURL("http://www.shelovesmath.com/trigonometry/polar-graphs/#DrawingGraphs")
# and then the "Rose" section


## Note: script works only for 6 roses!

## creating data frame
# first column: value of rose (between 0 and 1)
# second colum: corresponding color. See browseURL("http://www.stat.columbia.edu/~tzheng/files/Rcolor.pdf")
# third column: corresponding label 
df_roses <- data.frame(c(0.8, 0.5, 0.95, 0.8, 0.75, 0.6),
         c("lightgreen", "orange", "green", "lightgreen", "lightgreen", "grey90"),
         c("Soil Organic Carbon", "Yield", "Earthworms", "Water holding capacity", "Aggregate stability", "pH" ) ,
         stringsAsFactors = FALSE
         )
names(df_roses) <- c("Value", "Color", "Label")

View(df_roses)


## For our convenience: data frame with angles corresponding to the roses, 
# because a polar plot is angle-based
df_angles <- data.frame(2*pi/6*(0:5), 
                        2*pi/6*(1:6),
                        2*pi/6*seq(from = 0.5, to=5.5, by=1)
) 
names(df_angles) <- c("Start", "End", "Center")

#View(df_angles)


## first create empty plot, with labels
# labels cannot be added later :-(
radial.plot( lengths    = NA,
             radial.pos = NA,
             main       = "No-till versus conventional till",
             radial.lim = c(0,1),
             show.grid.labels = TRUE,
             show.radial.grid = TRUE,
             label.pos        = df_angles$Center,
             labels           = df_roses$Label
            )





## add roses one by one with for-loop
for (i in 1:6)
{
  vn_angle <- seq(from = df_angles$Start[i], to = df_angles$End[i], length=100)
  vn_rose  <-  abs( sin(vn_angle*6/2)*df_roses$Value[i] ) 
  
  radial.plot( lengths    = vn_rose,
               radial.pos = vn_angle,
               rp.type    = "p",
               line.col   = "black",
               poly.col   = df_roses$Color[i],
               add        = TRUE
          )
}


# draw the "no change" circle
n_no_change_value <- 0.6
vn_angle  <- seq(0, to = 2*pi, length=100)
vn_circle <- rep(x=n_no_change_value, times=100)
  
radial.plot( lengths      = vn_circle,
               radial.pos = vn_angle,
               radial.lim = c(0,1),
               rp.type    = "p",
               line.col   = "blue",
               add        = TRUE
          )

# add "no change" text
text(x      = 0, 
     y      = n_no_change_value + 0.05, # you can adjust this
     labels = "No change", 
     col    = "blue")

created by @LucSteinbuch