sm (version 2.0-1)

sm.sphere: Nonparametric density estimation for spherical data.

Description

This function creates a density estimate from data which can be viewed as lying on the surface of a sphere. Directional data form a principal example. The data are displayed in spherical form and a density estimate may be superimposed. The angle of view may be altered. An interactive panel is available to control some features of the estimate and the display. Only modest amounts of data may be used. The limit will depend on the memory available.

Usage

sm.sphere(lat, long, phi=0, theta=0, kappa=20, panel=F, hidden=F, 
   sphim=F, addpoints=F, ngrid=32)

Arguments

lat

a vector giving the latitude component of the data in degrees from the equator.

long

a vector giving the longitude component of the data in degrees east.

phi

the vertical rotation of the displayed sphere in degrees. The viewing position moves from the equator.

theta

the horizontal rotation of the displayed sphere. The viewing position moves in an easterly direction. When theta is set to 0, the origin of the spherical scales lies in the middle of the right hand side of the plot.

kappa

the smoothing parameter used to construct the density estimate. The kernel function is a Fisher distribution and kappa is its scale parameter. Larger values of kappa will produce smaller amounts of smoothing.

panel

a logical value which controls the appearance of a panel display. This panel may be used to alter a variety of aspects of the estimate and the plot in an interactive manner.

hidden

a logical value which, when set to T, will display the points which lie on the rear side of the displayed sphere. This argument will be ignored if sphim is set to T.

sphim

a logical value which controls whether a density estimate is constructed and displayed on the sphere in image form.

addpoints

a logical value which controls whether the data points are added to the plot of the density estimate.

ngrid

the number of points on each side of the regular grid over which the density estimate is evaluated.

Value

• a list containing the value of the smoothing parameter and the rotation angles of the displayed plot.

Side Effects

none.

Details

see Section 1.5 of the reference below.

References

Bowman, A.W. and Azzalini, A. (1997). Applied Smoothing Techniques for Data Analysis: the Kernel Approach with S-Plus Illustrations. Oxford University Press, Oxford.

See Also

sm.density

Examples

lat  <- rnorm(50, 10, 15)
long <- c(rnorm(25, 300, 15), rnorm(25, 240, 15))
par(mfrow=c(1,2))
sm.sphere(lat, long)
sm.sphere(lat, long, sphim=T, kappa=15)
par(mfrow=c(1,1))