[R] Range of circular data

[Waichler, Scott R]

I want to get the minimum arc (in degrees) needed to include a set of
compass directions.  I would like to use the range.circular() function
of the package circular, because that package understands a compass-type
of angle convention, but it gives results I don't understand.  Howver, I
can get the correct answer in the example below, 90 degrees, using the
CircStats package.  How can I make the circular package work for me?

> R.version.string
[1] "R version 2.6.1 (2007-11-26)"

> library(circular)
> y <- circular(c(45, 135), units = "degrees", template = "geographics")
> range.circular(y)
Circular Data:
Type = angles
Units = degrees
Template = geographics
Modulo = asis
Zero = 1.570796
Rotation = clock
[1] 0

Just in case range.circular() expects radians, I tried this:

> range.circular(rad(y))
Circular Data:
Type = angles
Units = degrees
Template = geographics
Modulo = asis
Zero = 1.570796
Rotation = clock
[1] 88.4292

I can get the correct answer using CircStats instead:

> library(CircStats)
> y <- rad(c(45, 135))
> 180*circ.range(y)/pi
  range
1    90

Thanks,
Scott Waichler
Pacific Northwest National Laboratory
scott.waichler _at_ pnl.gov