```
spsample(x, n, type, ...)
makegrid(x, n = 10000, nsig = 2, cellsize, offset = rep(0.5, nrow(bb)),
pretty = TRUE)
```

x

Spatial object;

`spsample(x,...)`

is a generic method for the
existing `sample.Xxx`

fumctions...

optional arguments, passed to the appropriate

`sample.Xxx`

functions; see NOTES for `nclusters`

and `iter`

n

(approximate) sample size

type

character;

`"random"`

for completely spatial random;
`"regular"`

for regular (systematically aligned) sampling;
`"stratified"`

for stratified random (one single random location in
each "cell"); `"nonaligned"`

for nonaligned systematic sampling
(nx random y coordinates, ny random x coordinates); `"hexagonal"`

for sampling on a hexagonal lattice; `"clustered"`

for clustered sampling;
`"Fibonacci"`

for Fibonacci sampling on the sphere (see references).bb

bounding box of the sampled domain; setting this to a smaller
value leads to sub-region sampling

offset

for square cell-based sampling types (regular, stratified,
nonaligned): the offset (position) of the regular
grid; the default for

`spsample`

methods is a random location in
the unit cell [0,1] x [0,1], leading to a different grid after
each call; if this is set to `c(0.5,0.5)`

, the returned grid is
not random (but, in Ripley's wording, "centric systematic"). For
line objects, a single offset value is taken, where the value varies within
the [0, 1] interval, and 0 is the beginning of each Line object, and 1
its end cellsize

if missing, a cell size is derived from the sample size

`n`

; otherwise, this cell size is used for all sampling methods
except `"random"`

nsig

for "pretty" cell size;

`spsample`

does not result in
pretty grids pretty

logical; if

`TRUE`

, choose pretty (rounded) coordinates-
SpatialPoints-class. The number of
points is only guaranteed to equal

`n`

when sampling is done in a
square box, i.e. (`sample.Spatial`

). Otherwise, the obtained number
of points will have expected value `n`

.When `x`

is of a class deriving from Spatial-class for which
no spsample-methods exists, sampling is done in the bounding box
of the object, using `spsample.Spatial`

. An overlay using
over may be necessary to select the features inside the geometry
afterwards.Sampling type `"nonaligned"`

is not implemented for line objects.Some methods may return NULL if no points could be successfully placed.`makegrid`

makes a regular grid that covers `x`

; when
`cellsize`

is not given it derives one from the number of grid
points requested (approximating the number of cells). It tries to
choose pretty cell size and grid coordinates.- x = "Spatial"
- sample in the bbox of
`x`

- x = "Line"
- sample on a line
- x = "Polygon"
- sample in a Polygon
- x = "Polygons"
- sample in a Polygons object, consisting of possibly
multiple Polygon objects (holes must be correctly defined, use
`checkPolygonsHoles`

if need be) - x = "SpatialPolygons"
- sample in an SpatialPolygons object; sampling
takes place over all Polygons objects present, use subsetting to vary
sampling intensity (density); holes must be correctly defined, use
`checkPolygonsHoles`

if need be - x = "SpatialGrid"
- sample in an SpatialGrid object
- x = "SpatialPixels"
- sample in an SpatialPixels object

Fibonacci sampling: Alvaro Gonzalez, 2010. Measurement of Areas on a Sphere Using Fibonacci and Latitude-Longitude Lattices. Mathematical Geosciences 42(1), p. 49-64

data(meuse.riv) meuse.sr = SpatialPolygons(list(Polygons(list(Polygon(meuse.riv)), "x"))) plot(meuse.sr) points(spsample(meuse.sr, n = 1000, "regular"), pch = 3) plot(meuse.sr) points(spsample(meuse.sr, n = 1000, "random"), pch = 3) plot(meuse.sr) points(spsample(meuse.sr, n = 1000, "stratified"), pch = 3) plot(meuse.sr) points(spsample(meuse.sr, n = 1000, "nonaligned"), pch = 3) plot(meuse.sr) points(spsample(meuse.sr@polygons[[1]], n = 100, "stratified"), pch = 3, cex=.5) data(meuse.grid) gridded(meuse.grid) = ~x+y image(meuse.grid) points(spsample(meuse.grid,n=1000,type="random"), pch=3, cex=.5) image(meuse.grid) points(spsample(meuse.grid,n=1000,type="stratified"), pch=3, cex=.5) image(meuse.grid) points(spsample(meuse.grid,n=1000,type="regular"), pch=3, cex=.5) image(meuse.grid) points(spsample(meuse.grid,n=1000,type="nonaligned"), pch=3, cex=.5) fullgrid(meuse.grid) = TRUE image(meuse.grid) points(spsample(meuse.grid,n=1000,type="stratified"), pch=3,cex=.5)

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