calc_sdd {aspace}R Documentation

Calculate and plot the Standard Distance Deviation (Standard Distance), and a Standard Deviation Box

Description

The dispersion of a set of points on a Cartesian plane can be described using the Standard Distance Deviation (SDD) or Standard Distance. For the purpose of geographic visualization, the SDD is typically portrayed as a circle with radius SDD centered on the mean center of a set of point observations. The orthogonal dispersion of a set of points can also be described using the standard deviation of the x- and y-coordinates of a set of point observations. The standard deviation of x- and y-coordinates can be geographically visualized using a box, with the edges set, respectively, to the standard deviation of the x- and y-coordinates.

Usage

calc_sdd(id = 1, filename = "SDD_Output.txt", centre.xy = centre, calccentre = TRUE, useWMC = FALSE, weightpoints = FALSE, weights = wts, destmat = activities, verbose = FALSE, plot = TRUE, plothv = TRUE, plotdest = TRUE, plotcenter = TRUE, box = TRUE)

Arguments

id A unique integer to identify the shape
filename A string indicating the ASCII textfile where shape coordinates will be written
centre.xy A vector of length 2, containing the x- and y-coordinates of the SDD centroid
calccentre Boolean: Set to TRUE if the mean center is to be calculated
useWMC Boolean: Set to TRUE if the mean center is to be computed with weighted coordinates
weightpoints Boolean: Set to TRUE if the point observations are to be weighted
weights Weights applied to point observations
destmat A 2-column matrix or data frame containing point coordinates
verbose Boolean: Set to TRUE if extensive feedback is desired on the standard output
plot Boolean: Set to TRUE if the SDD is to be plotted
plothv Boolean: Set to TRUE if the orthogonal N-S, E-W axes are to be plotted through the center
plotdest Boolean: Set to TRUE if the point observations are to be plotted
plotcenter Boolean: Set to TRUE if the mean center is to be plotted
box Boolean: Set to TRUE if the standard deviation of the x- and y-coordinates are to be plotted as a box

Details

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

Value

The result is a list of terms:

id Identifier for the SDD shape - it should be unique
calccentre True if mean centre is computed
Orig.x Original x-coordinate of center before mean center calculation
Orig.y Original y-coordinate of center before mean center calculation
CENTRE.x Actual, used x-coordinate of centre
CENTRE.y Actual, used y-coordinate of centre
SD.x Standard deviation of the x-coordinates
SD.y Standard deviation of the y-coordinates
SDD.radius SDD value, radius of the SDD
Box.area Area of the box formed by the standard deviation of the x- and y-coordinates
SDD.area Area of the SDD circle
useWMC Boolean: TRUE if the weighted mean center is used
WeightPoints Boolean: TRUE if point observations are weighted

Note

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 SDD has a unique identifier. The output ASCII coordinate file can be further processed using the makeshapes function to generate an ESRI Shapefile for SDD polygons.

Author(s)

Tarmo K. Remmel, Ron Buliung

See Also

ellipse3, calc_mcp, calc_sde, makeshapes

Examples

calc_sdd(id = 1, filename = "SDD_Output.txt", centre.xy = centre, calccentre = TRUE, useWMC = FALSE, weightpoints = FALSE, destmat = activities, verbose = FALSE, plot = TRUE, plothv = TRUE, plotdest = TRUE, plotcenter = TRUE, box = TRUE)

[Package aspace version 1.2 Index]