aspace (version 2.5)

calc_sdd: Calculate the Standard Distance Deviation (Standard Distance)

Description

This function computes the Standard Distance Deviation (SDD) or Standard Distance from a set of points.

Usage

calc_sdd(id=1, filename="SDD_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 SDD estimate

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 centre

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 grid points within the convex hull 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_sdd function

verbose

Boolean: Set to TRUE if extensive feedback is desired on the standard output

Value

• The result is a list of terms:
• id
  Identifier for the SDD shape - it should be unique
• calccentre
  Boolean: TRUE if mean centre is computed
• weighted
  Boolean: TRUE if the weighted mean centre is to be used instead
• 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
• SDD.radius
  SDD value, radius of the SDD
• SDD.area
  Area of the SDD circle

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

plot_sdd, calc_mcp, calc_sde, calc_box, ellipse3, makeshapes, mcp, gridpts

Examples

calc_sdd(id=1, filename="SDD_Output.txt", centre.xy=NULL, calccentre=TRUE, 
weighted=TRUE, weights=wts, CMD.npts=10000, points=activities, verbose=TRUE)