calc_box {aspace}R Documentation

Calculate the Standard Deviation Box

Description

The orthogonal dispersion of a set of points can be described using the standard deviation of the x- and y-coordinates of a set of point observations. The orthogonal dispersion can then be visualized with a Standard Deviation Box. This function computes the properties of the Standard Deviation Box (SD Box) from a set of point observations.

Usage

calc_box(id=1, filename="BOX_Output.txt", centre.xy=NULL, calccentre=TRUE, weighted=FALSE, weights=NULL, CMD.npts=10000, points=activities, verbose=FALSE)

Arguments

id A unique integer to identify a SD Box
filename A string indicating the ASCII textfile where the box coordinates will be written
centre.xy A vector of length 2, containing the x- and y-coordinates of the geographic centre of the SD Box
calccentre Boolean: Set to TRUE if the mean center is to be calculated
weighted Boolean: Set to TRUE if the weighted mean center is to be computed with weighted coordinates
weights Weights applied to point observations, number of weights should equal the number of observations
CMD.npts The approximate number of points to generate for the centre of minimum distance (CMD) calculation
points A 2-column matrix or data frame containing the set of point observations input to the calc_box function
verbose Boolean: Set to TRUE if extensive feedback is desired on the standard output

Details

This function is most powerful when used repetitively within a loop to compute the SD Box for subsets of points stored in a large table.

Value

The returned result is a list:

id Identifier for the SD Box shape - it should be unique
calccentre Boolean: TRUE if the mean centre was estimated
weighted Boolean: TRUE if the weighted mean centre was estimated
CENTRE.x X-coordinate of the centre
CENTRE.y Y-coordinate of the centre
central.x X-coordinate of the identified central feature
central.y Y-coordinate of the identified central feature
median.x X-coordinate of median centre, median value of the X-coordinate vector
median.y Y-coordinate of median centre, median value of the Y-coordinate vector
CMD.x X-coordinate of estimated centre of minimum distance
CMD.y Y-coordinate of estimated centre of minimum distance
SD.x Orthogonal standard deviation in the x-axis
SD.y Orthogonal standard deviation in the y-axis
Box.area Area of the standard deviation box
NW.coord North-west coordinates of SD Box
NE.coord North-east coordinates of SD Box
SW.coord South-west coordinates of SD Box
SE.coord South-east coordinates of SD Box

Note

Results are stored in the r.BOX object (required for graphical visualization using the plot_box function). This function can be used on its own (once) or repetitively in a loop to process grouped point data stored in a larger table. When used repetitively, be sure to increment the id parameter to ensure that each SD Box has a unique identifier. The output ASCII coordinate file can be further processed using the makeshapes function to generate an ESRI Shapefile for SD Box polygons.

Author(s)

Randy Bui, Ron N. Buliung, Tarmo K. Remmel

See Also

plot_box, calc_mcp, calc_sde, calc_sdd, ellipse3, makeshapes, mcp, gridpts, wtd.var

Examples

calc_box(id=1, filename="BOX_Output.txt", centre.xy=NULL, calccentre=TRUE, weighted=FALSE, weights=NULL, CMD.npts=10000, points=activities, verbose=TRUE)

[Package aspace version 2.2 Index]