grtsarea: Select a Generalized Random-Tesselation Stratified (GRTS) Sample of an Area Resource

Description

This function select a GRTS sample of an area resource. The 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.

Usage

grtsarea(shapefilename = NULL, areaframe, samplesize = 100,
  SiteBegin = 1, shift.grid = TRUE, startlev = NULL, maxlev = 1,
  maxtry = 1000)

Arguments

shapefilename

Name of the input shapefile. If shapefilename equals NULL, then the shapefile or shapefiles in the working directory are used. The default is NULL.

areaframe

Data frame containing id, mdcaty and mdm.

samplesize

Number of points to select in the sample. The default is 100.

SiteBegin

First number to start siteID numbering. The default is 1.

shift.grid

Option to randomly shift the hierarchical grid. 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 11. The default is NULL.

maxlev

Maximum number of hierarchical levels to use for the GRTS grid, which cannot be greater than 11. The default is 11.

maxtry

Maximum number of iterations for randomly generating a point within a grid cell to select a site when type.frame equals "area". The default is 1000.

Value

Data frame of sample points containing: siteID, id, x, y, mdcaty, and weight.

Other Functions Required

pointInPolygonObj: C function to determine which points in a set of points are located within a specified polygon
numLevels: C function to determine the number of levels for hierarchical randomization
constructAddr: C function to construct the hierarchical address for all points
ranho: C function to construct the randomized hierarchical address for all points
pickGridCells: C function to select grid cells that get a sample point
insideAreaGridCell: C function to determine ID value and clipped polygon area for shapefile records contained in the selected grid cells
selectrecordID: select a shapefile record from which to select a sample point
pickAreaSamplePoints: C function to pick sample points in the selected grid cells