geoR (version 1.0-0)

polygrid: Coordinates of Points Inside a Polygon

Description

This function builds a rectangular grid and extracts points which are inside of an internal polygonal region.

Usage

polygrid(xgrid, ygrid, poly, vec.inout = FALSE)

Arguments

xgrid

grid values in the x-direction.

ygrid

grid values in the y-direction.

poly

a matrix with the polygon coordinates.

vec.inout

logical. If TRUE a logical vector is included in the output indicating whether each point of the grid is inside the polygon. Defaults to FALSE.

Value

• A list with components:
• xypoly
  an $n \times 2$ matrix with the coordinates of the points inside the polygon.
• vec.inout
  logical, a vector indicating whether each point of the rectangular grid is inside the polygon. Only returned if vec.inout = TRUE.

Details

This function requires the package splancs.

The function works as follows: First it creates a grid using the Rfunction expand.grid and then it uses the function inout from the package splancs to extract the points of the grid which are inside the polygon. Within the package geoR this function is typically used to select points in a non-rectangular region to perform spatial prediction using krige.bayes, krige.conv or ksline. It is also useful to produce image or perspective plots of the prediction results.

References

Further information about geoR can be found at: http://www.maths.lancs.ac.uk/~ribeiro/geoR.html.

See Also

expand.grid, inout.

Examples

poly <- matrix(c(.2, .8, .7, .1, .2, .1, .2, .7, .7, .1), ncol=2)
plot(0:1, 0:1, type="n")
lines(poly)
poly.in <- polygrid(seq(0,1,l=11), seq(0,1,l=11), poly, vec=T)
points(poly.in$xy)