oce (version 0.2-1)

interpBarnes: Grid data using Barnes algorithm

Description

Grid data using Barnes algorithm.

Usage

interpBarnes(x, y, z, w=NULL, xg=NULL, yg=NULL, xr=NULL, yr=NULL, 
gamma=0.5, iterations=2)

Arguments

x

a vector of x locations.

y

a vector of y locations.

z

a vector of z values, one at each (x,y) location.

w

a optional vector of weights at the (x,y) location. If not supplied, i.e. if a NULL value, then a weight of 1 is used for each point, which means equal weighting. Higher weights give data points more influence.

xg

an optional vector defining the x grid. If not supplied, this will be determined from the x data, using pretty(x, n=50).

yg

a optional vector defining the y grid. If not supplied, this will be determined from the x data, using pretty(y, n=50). In the special case with all y values identical, yg is set to that value. This is useful for

xr

a optional value defining the width of the radius ellipse in the x direction. If not supplied,

yr

an optional value defining the height of the radius ellipse in the y direction.

gamma

grid-focussing parameter. At each iteration, xr and yr are reduced by a factor of sqrt(gamma).

iterations

number of iterations.

Value

• A list containing xg, the x-grid, yg, the y-grid, and zg, the gridded value.

concept

tide

Details

The algorithm follows that described by Koch et al. (1983).

References

S. E. Koch and M. DesJardins and P. J. Kocin, 1983. ``An interactive Barnes objective map anlaysis scheme for use with satellite and conventional data,'' J. Climate Appl. Met., vol 22, p. 1487-1503.

Examples

library(oce)

# Contouring example, with wind-speed data from Koch et al. (1983)
data(wind)
u <- interpBarnes(wind$x, wind$y, wind$u)
contour(u$xg, u$yg, u$zg, col="red", labcex=1)
text(wind$x, wind$y, wind$u, cex=0.7, col="blue")

# One-dimensional example, smoothing a salinity profile
data(ctd)
p <- ctd$data$pressure
y <- rep(1, length(p)) # fake y data, with arbitrary value
S <- ctd$data$salinity
pg <- pretty(p, n=100)
g <- interpBarnes(p, y, S, xg=pg, xr=2)
plot(S, p, cex=0.5, col="blue", ylim=rev(range(p)))
lines(g$zg, g$xg, col="red")