On 02/02/15 16:26, p_connolly wrote:
Just what is meant by dummy points as referred to by the help for the deldir() function? I understood they indicated the boundary beyond which triangulation would cease. I thought I would need the x/y elements (as described in the help file at the end of the description of the use of the dpl argument) to describe ad hoc dummy points as way to define a polygon or two as a boundary. However, it gives this error: Error in xd[-drop] : only 0's may be mixed with negative subscripts Something internal is doing the negative subscripting. I tried ndx/ndy instead of x/y but it evidently refers only to a rectangle so not what I need. Am I barking up the wrong tree altogether? Is the boundary defined somewhere else entirely? I need to get that clear before I am able to provide useful example code.
The dummy points have nothing to do with any "boundary". In fact they have nothing much to do with anything, really! :-) They are a hangover from the original purpose of deldir which was to assist in a numerical integration needed for the maximum likelihood estimation of the intensity function of an inhomogeneous Poisson process. I really should get rid of them, but that would require a bit of work and re-writing of code and help files, and they do no real harm so I have decided to apply the "If it ain't broke don't fix it." principle.
The deldir function creates a Delaunay triangulation/Dirichlet tessellation inside a "rectangular window" (denoted by "rw" in the argument list). This is the only boundary invoked or involved.
The function plot.tile.list() will *plot* the Dirichlet tessellation "clipped" to a specified polygon. But that is just for *plotting*. I am not sure that I really understand the idea of a "boundary beyond which the triangulation ceases". The Delaunay triangulation is a finite structure; its outer boundary is the convex hull of the set of points being triangulated. You cannot confine it to a smaller region without losing some of those points.
If you can explain what you really want to do, perhaps I can help. cheers, Rolf -- Rolf Turner Technical Editor ANZJS Department of Statistics University of Auckland Phone: +64-9-373-7599 ext. 88276 Home phone: +64-9-480-4619 ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
