This function select a GRTS sample of a finite 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.
grtspts(src.frame="shapefile", shapefilename=NULL, ptsframe, samplesize=100,
SiteBegin=1, shift.grid=TRUE, do.sample=TRUE, startlev=NULL, maxlev=11)source of the frame, which equals "shapefile" if the frame is to be read from a shapefile, or "att.frame" if the frame is included in ptsframe. The default is "shapefile".
name of the input shapefile. If src.frame equal "shapefile" and shapefilename equals NULL, then the shapefile or shapefiles in the working directory are used. The default is NULL.
a data frame containing id, x, y, mdcaty, and mdm.
number of points to select in the sample. The default is 100.
number to use for first site in the design. The default is 1.
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.
option to select a sample, where TRUE means select a sample and FALSE means return the entire sample frame in reverse hierarchical order. The default is TRUE.
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 11. The default is NULL.
maximum number of hierarchical levels to use for the GRTS grid, which cannot be greater than 11. The default is 11.
A data frame of GRTS sample points containing: SiteID, id, x, y, mdcaty, and weight.
Stevens, D.L., Jr., and A.R. Olsen. (2004). Spatially-balanced sampling of natural resources. Journal of the American Statistical Association 99, 262-278.