aspace (version 2.5)

calc_box: 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

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

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.

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)