# gridSample

From dismo v1.3-3
by Robert Hijmans

##### Stratified regular sample on a grid

Sample points from xy, using a grid (raster) as stratification. Up to n points are sampled from each stratum (cell). For "chessboard" sampling (i.e. sampling from half the cells), use the argument `chess='black'`

, or `chess='white'`

.

- Keywords
- spatial

##### Usage

`gridSample(xy, r, n=1, chess='')`

##### Arguments

- xy
A two column matrix or data.frame with x and y coordinates (or longitude and latitude), or a SpatialPoints* object

- r
Raster* object

- n
Maximum number of samples per cell

- chess
Character. '', 'black', or 'white'. If 'black' or 'white', "chess-board" sampling is used. I.e. only the 'white' fields, or only the 'black' fields are sampled. Cell number 1 (the upper left corner of

`r`

) is white.

##### Value

A two column matrix with x and y coordinates (or longitude and latitude)

##### See Also

##### Examples

```
# NOT RUN {
x <- rnorm(1000, 10, 5)
y <- rnorm(1000, 50, 5)
xy <- cbind(x,y)
res <- 5
r <- raster(extent(range(xy[,1]), range(xy[,2])) + res)
res(r) <- res
samp <- gridSample(xy, r, n=1)
plot(xy, cex=0.1)
points(samp, pch='x', col='red')
# }
```

*Documentation reproduced from package dismo, version 1.3-3, License: GPL (>= 3)*

### Community examples

Looks like there are no examples yet.