Function to construct edges based on a tolerance angle and a maximum distance
This function creates an object of class
nb (defined in the library spdep) containing a connexion diagram. The edges between sites are based on a tolerance angle and a maximum distance. The angle is directional; its direction is always from the bottow to the top of the screen.
tolerance.nb(coords, unit.angle = "degrees", max.dist, tolerance, rot.angle, plot.sites=FALSE)
- A matrix or a data frame containing the X and Y coordinates of the study sites.
- Character. The measurement units in which angles are defined: either "degrees" (default) or "radians".
- Numeric. The maximum distance of an edge linking two sites together.
- Numeric. The tolerance angle in which a site can influence another site. The angle is measured vertically and from bottom to top of the pictures after rotation of the points.
- Numeric, optional. An angle at which a set of coordinates should be rotated before creating the connexion diagram. The set of coordinates is rotated counterclockwise. Negative values will produce a clockwise rotation.
- Logical (
FALSE) determining if the site should be plotted in a graphic window. This graph allows one to make sure the points are rotated in a correct direction.
Even though this function creates a connexion diagram based on a tolerance angle going from the bottom to the top of the screen, the resulting object is symmetric, meaning that a site influences another and vice versa. The final object does not represent a directional connexion network.
The function returns an object of class
nbwith a list of integer vectors corresponding to neighbour region numbers.
This function was not design to handle a large number of rows in
To use this function for a set of coordinates with more than 1500 entries is memory intensive.
set.seed(1) ex.data<-cbind(runif(50),rexp(50)) ### Construct object of class nb with a tolerance angle of 30 degrees ### and a maximum distance of 2 m. nb.ex<-tolerance.nb(ex.data, unit.angle = "degrees", max.dist=1, tolerance = 30) ### Construct object of class nb with a tolerance angle of 30 degrees ### and a maximum distance of 2 m. The coordinates are rotated at an angle ### of 45 degrees counterclockwise. nb.ex2<-tolerance.nb(ex.data, unit.angle = "degrees", max.dist=1, tolerance = 30, rot.angle = 45) ### Construct object of class nb with a tolerance angle of pi/8 radians ### and a maximum distance of 1.5 m. The coordinates are rotated at ### an angle of pi/4 radians clockwise. nb.ex3<-tolerance.nb(ex.data, unit.angle = "radians", max.dist=1.5, tolerance = pi/8, rot.angle = -pi*2/3) par(mfrow=c(1,3)) plot(nb.ex,ex.data,asp=1) plot(nb.ex2,ex.data,asp=1) plot(nb.ex3,ex.data,asp=1)