Manipulating x axis labelling for a feather plot - r

Question

I have some wind speed and direction data over a course of some time and I need to plot it into a feather plot.
After surfing the web for some time, I find a function someone wrote to plot the feather plot that works for me (Thank you if you are reading this!!). My problem now is that I don't know how to manipulate the labelling of the x-axis.
After the plotting, the figure looks like this:
Now the x-axis doesn't look too bad here, but imagine I have 200 data points (and thus ticks) instead of 10, and the axis ticks can get a bit confusing. So I was hoping someone can help me manipulate the x-axis, specifically messing with the ticks.
The code to plot the figure is:
stg <- scan(what="", sep="\n")
9/20/15_12:00 2.597058824 157.9411765
9/21/15_0:00 2.177192982 185.1754386
9/21/15_12:00 2.577391304 189.2173913
9/22/15_0:00 1.984955752 237.4336283
9/22/15_12:00 3.993859649 252.6315789
9/23/15_0:00 1.613392857 175.5357143
9/23/15_12:00 3.849166667 216.8333333
9/24/15_0:00 2.138135593 117.0338983
9/24/15_12:00 3.32605042 216.302521
9/25/15_0:00 1.490178571 239.8214286
df <- read.table(textConnection(stg), sep="")
colnames(df) <- c("Time", "wsp", "wdir")
df$PTime <- as.POSIXct(df$Time, format="%m/%d/%y_%H:%M")
feather.plot2 <- function (r, theta, xpos, yref = 0, use.arrows = TRUE, col.refline = "lightgray",
fp.type = "s", main = "", xlab = "", ylab = "", xlabels = NULL,
...)
{
if (missing(xpos))
xpos <- 1:length(theta)
if (fp.type == "m")
theta <- 5 * pi/2 - theta
x <- r * cos(theta)
y <- r * sin(theta)
xmult <- diff(range(xpos))/(diff(range(y)) * 2)
x <- x * xmult
xlim <- range(c(xpos, x + xpos))
ylim <- range(c(y, yref))
oldpin <- par("pin")
xdiff <- xlim[2] - xlim[1]
ydiff <- ylim[2] - ylim[1]
plot(0, xlim = xlim, ylim = ylim, type = "n", main = main,
xlab = xlab, ylab = ylab, axes = TRUE, xaxt = "n")
box()
if (is.null(xlabels))
axis(1)
else axis(1, at = xpos, labels = xlabels)
abline(h = yref, col = col.refline)
if (use.arrows)
arrows(xpos, yref, xpos + x, y, length = 0.1, ...)
else segments(xpos, yref, xpos + x, y, ...)
par(pin = oldpin)
}
feather.plot2(df$wsp, df$wdir, fp.type="m", xlabels=df$PTime)
And what I want is something like having big ticks for 12:00, and smaller ticks for 0:00, like in this figure:
Although I don't know why the label for this figure comes out as "Sun - Thu" instead of dates...
The code for this figure is:
daterange=c(min(df$PTime), max(df$PTime))
plot(x=df$PTime, y=df$wsp, xaxt="n", type="l")
axis.POSIXct(1, at=seq(daterange[1], daterange[2], by="day"))
axis.POSIXct(1, at=seq(daterange[1], daterange[2], by="12 hours"), tcl = -0.3, labels=FALSE )
I've tried using using these axis commands on the feather plot, but it did not work. So I'd appreciate any help/advice. Thank you so much!!

Answer 1

I'm seeing two requests: Major and minor ticks; and More compact axis annotation of date-times. Step 1: Suppress the default axis creation. Step 2: The usual manor is to label the major ticks, so we would determine the proper location of those ticks and give a format specification to the labels. Step 3: place the minor tick marks. Most of this you've already figured out, and I would have thought the format problem was the easiest one to solve, so let's see:
plot(x=df$PTime, y=df$wsp, xaxt="n", type="l")
axis.POSIXct(1, at=seq(daterange[1], daterange[2], by="day"), format="%m-%d %H%P",
lwd.ticks=2)
axis.POSIXct(1, at=seq(daterange[1], daterange[2], by="12 hours"),
tcl = -0.3, labels=FALSE )
Seems to succeed at what I think are your goals. The use of by = "day" may be what leads the interpreter to choose the three letter abbrev of day names. (I don't really know.)