Description Usage Arguments Details Value Author(s) References See Also Examples
Draws an equiprobable unstratified Generalized Random
Tessellation Stratified (GRTS) sample from a SpatialPoints*
object
1  grts.point(x, n, over.n = 0)

x 
A 
n 
Sample size. The number of sample points to draw from 
over.n 
Oversample size. The number of 'oversample' points to draw
from 
This is a wrapper for the grts
function in package spsurvey
.
This simplifies calling grts
when equiprobable samples are
desired. It extends the valid input frame types to SpatialPoints
objects
(i.e., no attributes),
rather than just SpatialPointsDataFrame
objects. For more
complicated designs (e.g., variable probability, stratification), call
grts
directly.
A SpatialPointsDataFrame
containing locations in the GRTS sample, in
order they are to be visited. Attributes of the sample points (in the embedded data frame) are
as follows:
sampleID
: Unique identifier for sample points. This
encodes the GRTS ordering of the sample. The output object
comes presorted in GRTS order.
If the sample becomes unGRTSordered, resort
by sampleID
(i.e., samp < samp[order(samp$sampleID),]
).
pointType
: A string identifying regular sample points (pointType=="Sample"
)
and oversample points (pointType=="OverSample"
).
geometryID
: The ID of the point in x
which was sampled. The
ID of points in x
are row.names(geometry(x))
.
Any attributes of the original points (in x
).
Trent McDonald
Stevens, D. L. and A. R. Olsen (1999). Spatially restricted surveys over time for aquatic resources. Journal of Agricultural, Biological, and Environmental Statistics 4 (4), 415428.
Stevens, D. L. and A. R. Olsen (2004). Spatially balanced sampling of natural resources. Journal of the American Statistical Association 99, 262278.
grts.line
, grts.polygon
, hal.point
,
sdraw
1 2 3 4 5 6 7 8 9 10 11  # Draw sample
WA.city.samp < grts.point(WA.cities,100,50)
# Plot
plot( WA.cities, pch=16, cex=.5 )
# Plot 'sample' locations
plot( WA.city.samp[ WA.city.samp$pointType == "Sample", ], pch=1, add=TRUE, col="red" )
# Plot 'over sample' locations
plot( WA.city.samp[ WA.city.samp$pointType == "OverSample", ], pch=2, add=TRUE, col="blue" )

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