in.out {mgcv} | R Documentation |

## Which of a set of points lie within a polygon defined region

### Description

Tests whether each of a set of points lie within a region defined by one or more (possibly nested) polygons. Points count as ‘inside’ if they are interior to an odd number of polygons.

### Usage

```
in.out(bnd,x)
```

### Arguments

`bnd` |
A two column matrix, the rows of which define the vertices of polygons defining the boundary of a region.
Different polygons should be separated by an |

`x` |
A two column matrix. Each row is a point to test for inclusion in the region defined by |

### Details

The algorithm works by counting boundary crossings (using compiled C code).

### Value

A logical vector of length `nrow(x)`

. `TRUE`

if the corresponding row of `x`

is inside
the boundary and `FALSE`

otherwise.

### Author(s)

Simon N. Wood simon.wood@r-project.org

### References

https://www.maths.ed.ac.uk/~swood34/

### Examples

```
library(mgcv)
data(columb.polys)
bnd <- columb.polys[[2]]
plot(bnd,type="n")
polygon(bnd)
x <- seq(7.9,8.7,length=20)
y <- seq(13.7,14.3,length=20)
gr <- as.matrix(expand.grid(x,y))
inside <- in.out(bnd,gr)
points(gr,col=as.numeric(inside)+1)
```

*mgcv*version 1.9-1 Index]