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

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calc_sdd(id=1, filename="SDD_Output.txt", centre.xy=NULL, calccentre=TRUE, 
weighted=FALSE, weights=NULL, 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

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

Details

Use the sddloc (coordinates) and sddatt(attributes) to produce shapefiles using the convert.to.shapefile and write.shapefile from the shapefiles library

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

SDD.radius

SDD value, radius of the SDD

SDD.area

Area of the SDD circle

Note

Results are stored in the r.SDD object (required for plot_sdd). 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 shapefiles package to generate an ESRI Shapefile for SDD polygons.

Author(s)

Randy Bui, Ron Buliung, Tarmo K. Remmel

See Also

plot_sdd, calc_sde, calc_box

Examples

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## SDD example
calc_sdd(id=1, filename="SDD_Output.txt", centre.xy=NULL, calccentre=TRUE, 
weighted=FALSE, weights=NULL, points=activities, verbose=FALSE)

## plot_sdd by default takes as input the result produced from the calc_sdd, read from the current workspace. 

## SDD to shapefile example (exclude the comments below to run script)
## shp <- convert.to.shapefile(sddloc,sddatt,"id",5)
## write.shapefile(shp, "SDD_Shape", arcgis=T)

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