[R] Polar graph of time and tide

Gabor Grothendieck ggrothendieck at gmail.com
Wed May 2 15:57:24 CEST 2007

On 5/2/07, Jim Lemon <jim at bitwrit.com.au> wrote:
> Alan E. Davis wrote:
> > I have been trying to visualize times of lowest tides, month by month.
> >  I have tide predictions with times either in unix time or a text
> > format, and heights in feet or meters.  I had been able to derive the
> > clock times of each prediction.   I would now like to graph this data
> > with points showing heights as "r" and times as "theta", from 0000 to
> > 2355.  There is a seasonal component: I am interested in displaying
> > times of lowest tides in particular.
> >
> > I am sure this is so simple as to burden those on the list; I however
> > have spent two evenings trying to figure out how to use polar.plot,
> > and I'm not sure that's the best way to do this.  May I request some
> > advice?  The docs with polar.plot are not complete, I fear.
> >
> > Thank you, begging for your indulgence,
> >
> Hi Alan,
> Earl Glynn's advice is spot-on if you are trying to map tides onto the
> diurnal cycle. However, I get the impression that you want an annual
> cycle. If this is the case, it is probably best to go to the underlying
> function, radial.plot. Here is an example with some imaginary tides.
> lowtide<-sin(seq(1:12)+sin(seq(1,24,by=2)/10))
> lowtide<-rescale(lowtide,c(0,2355))
> month.abbr<-c("jan","Feb","Mar","Apr","May","Jun",
>  "Jul","Aug","Sep","Oct","Nov","Dec")

> radial.plot(lowtide,labels=month.abbr,rp.type="s")

Note that month.abb is built into R so one could eliminate the
month.abbr<- line and write:

radial.plot(lowtide, labels = month.abb, rp.type = "s")

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