calc_box {aspace} | R Documentation |
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.
calc_box(id=1, filename="BOX_Output.txt", centre.xy=NULL, calccentre=TRUE, weighted=FALSE, weights=NULL, CMD.npts=10000, points=activities, verbose=FALSE)
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 |
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.
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 |
Results are stored in the r.BOX object (required for graphical visualization using the plot_box function). 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 makeshapes function to generate an ESRI Shapefile for SD Box polygons.
Randy Bui, Ron N. Buliung, Tarmo K. Remmel
plot_box
, calc_mcp
,
calc_sde
, calc_sdd
,
ellipse3
, makeshapes
,
mcp
, gridpts
, wtd.var
calc_box(id=1, filename="BOX_Output.txt", centre.xy=NULL, calccentre=TRUE, weighted=FALSE, weights=NULL, CMD.npts=10000, points=activities, verbose=TRUE)