aspace (version 0.1)

calc.sdd: 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

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

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.

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)