contoureR {contoureR}

contoureR: Contouring of Non-Regular Three-Dimensional Data

Description

Create contour lines for a non regular series of points, potentially from a non-regular canvas.

Details

The contoureR package executes linear interpolation on a delaunay triangulated mesh strung between three-dimensional (3D) points supplied by the user. Contours are calculated across the surface constrained by the convex hull of the supplied data.

Usually, the well known functions such as contourLines from the grDevices package, expect (or rather, require) data to be regular, this means that a rectangular array or matrix of x and y coordinate pairs, each with a corresponding z value is to be modelled – that is to say the cartesian product of a numeric vector of x values of length n, with a numeric vector of y values having length m, used to produce a set of (m x n) unique points that have been concurrently provided with exactly (m x n) z values.

By restricting values to the above format, this in turn limits the region of analysis to square/rectangular canvasses (ie plane defined by geometric and orthogonal vectors parallel to the x and y axes and range bound by the [xmin,xmax] and [ymin,ymax] in the above x and y input numeric vectors, respectively). This restriction, from time-to-time, can be very inconvenient, and is a primary objective and purpose for the creation of this package.

As suggested in the previous paragraph, the contoureR package, on the other hand, has no such orthogonality / regularity requirement and can therefore be applied over obscurely shaped regions such as triangles, circles, polygons and the like. To demonstrate this, in the example provided on the current page, an equation is contoured, where firstly the x and y data is randomly selected (non regular), and then the set of values is subsequently constrained by a bounding (limiting) circle.

Note, for the moment, the only restriction is that for polygon-type regions to be modelled, then these regions must not have holes, since these will be filled coarsely when the Deleaunaymesh gets generated, however, in future revisions, this obstacle should be easily addressed via parameter defining a manual exclusion list of points.

See Also

getContourLines, contourLinesR and contourWalker

Examples

# Contour Lines for a Function, Constrained to a limited domain
# Example of the provision of non-regular data
library(contoureR)
library(ggplot2)
a  = -2; b = +2; n  = 150
x  = runif(n*n,a,b)
y  = runif(n*n,a,b)
df = data.frame(x,y)
df$z   = with(df,-x*y*exp(-x^2-y^2))
df.sub = subset(df,x^2 + y^2 < 2)
df.cnt = getContourLines(df.sub,nlevels=20)
ggplot(data=df.cnt,aes(x,y,group=Group,colour=z)) + geom_path() + theme_bw()