grtsarea {psurvey.design} | R Documentation |
This function select a GRTS sample of an area resource. This function uses hierarchical randomization to ensure that the sample will include no more than one point per cell and then picks a point in selected cells using a center-peaked distribution. The function can impose a probability distribution on permutation selection in the hierarchical randomization.
grtsarea(src.frame="shapefile", shapefilename=NULL, xy.frame, areaframe, samplesize=100, SiteBegin=1, shift.grid=TRUE, startlev=NULL, maxlev=12, maxtry=1000, acept=1, prm.prb=rep(1, 24), ext.prb.fcn=NULL, fpar=NULL)
src.frame |
source of the frame, which equals "shapefile" if frame is to be read from a shapefile and otherwise is equal to NULL. The default is "shapefile". |
shapefilename |
name of the input shapefile. If src.frame equal "shapefile" and shapefilename equals NULL, then the shapefile or shapefiles in the currrent directory are used. The default is NULL. |
xy.frame |
name of the data structure containing xy-coordinates for elements in the frame, where format depends on type.frame. If src.frame equals "shapefile", then equal to NULL. |
areaframe |
a data frame containing id, mdcaty and mdm. |
samplesize |
number of points to select in the sample. The default is 100. |
SiteBegin |
number to use for first site in the design. The default is 1. |
shift.grid |
option to randomly shift the hierarchical grid, where TRUE means shift the grid and FALSE means do not shift the grid, which is useful if one desires strict spatial stratification by hierarchical grid cells. The default is TRUE. |
startlev |
initial number of hierarchical levels to use for the GRTS grid, which must be less than or equal to maxlev (if maxlev is specified) and cannot be greater than 12. The default is NULL. |
maxlev |
maximum number of hierarchical levels to use for the GRTS grid, which cannot be greater than 12. The default is 12. |
maxtry |
maximum number of iterations for randomly generating a point The default is 1000. |
acept |
parameter that controls peakedness of a center-peaked distribution, which must be between 0 and 1. A value of 0 gives a triangular distribution, and a value of 1 gives a uniform distribution. The default is 1. |
prm.prb |
specifies the permutation distribution. The default is an equiprobable distribution. |
ext.prb.fcn |
a user-defined function that calculates the inclusion probability for a vector of points with coordinates (x,y). The function must return a non-negative value (which can be zero) for any point within the grid region, and must return zero for (x,y) values outside the grid region. If a functions is not provided and src.frame is either "polygons" or "rectangle", a function is created that returns a vector of inclusion probabilities calculated using the multi-density category multiplier (mdm) values provided in areaframe. The default is NULL. |
fpar |
an optional list of parameters for ext.prb.fcn. The default is NULL. |
A data frame of GRTS sample points containing: SiteID, id, x, y, mdcaty, and weight.
Tony Olsen Olsen.Tony@epa.gov
Tom Kincaid Kincaid.Tom@epa.gov
Stevens, D.L., Jr., and A.R. Olsen. (2004). Spatially-balanced sampling of natural resources. Journal of the American Statistical Association 99: 262-278.