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

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

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

Details

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

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

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

Note

Results are stored in the r.BOX object (required for plot_box). 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 SD BOX has a unique identifier. The output ASCII coordinate file can be further processed using the shapefiles package to generate an ESRI Shapefile for SD BOX polygons.

Author(s)

Randy Bui, Ron N. Buliung, Tarmo K. Remmel

See Also

plot_box, calc_sde, calc_sdd, wtd.var

Examples

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## BOX example
calc_box(id=1, filename="BOX_Output.txt", centre.xy=NULL, calccentre=TRUE, 
weighted=FALSE, weights=NULL, points=activities, verbose=FALSE)

## plot_box by default takes as input the result produced from the calc_box, read from the current workspace. 

## SD Box to shapefile example (exclude the comments below to run script)
## shp <- convert.to.shapefile(boxloc,boxatt,"id",5)
## write.shapefile(shp, "BOX_Shape", arcgis=T)

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