polygrid {geoR} | R Documentation

## 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, borders, vec.inout = FALSE, ...)

### Arguments

`xgrid` | grid values in the x-direction.
`ygrid` | grid values in the y-direction.
`borders` | a matrix with polygon coordinates defining the borders of the region.
`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`.
`...` | arguments to be passed to the splancs function `inout`.

### Details

This function requires the package splancs.

The function works as follows: First it creates a grid using the R function `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.

### Value

A list with components:

`xypoly` | an n x 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`.

### Author(s)

Paulo Justiniano Ribeiro Jr. Paulo.Ribeiro@est.ufpr.br,
Peter J. Diggle p.diggle@lancaster.ac.uk.

### References

Further information on the package geoR can be found at:
http://www.est.ufpr.br/geoR.

### See Also

`expand.grid`, `inout.`

### Examples

    if(require(splancs)){
     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=TRUE)
     points(poly.in$xy)
    }

[Package geoR version 1.5-7 Index]