Hello geo list,

I have a question about the bdist function in spatstat when applied to tiles.    The documentation for bdist.tiles says:
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Details
This function computes, for each tile s[[i]] in the tessellation X, the shortest distance from s[[i]] to the boundary of the window W containing the tessellation.
Value
A numeric vector, giving the shortest distance from each tile in the tessellation to the boundary of the window. Entries of the vector correspond to the entries of tiles(X).
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*** From what point on the tile does this function measure?  ****

I am interesting is doing Dirichlet (Voronoi) tessellations  (using dirichlet()), but I want to keep separate tiles that hit the window boundary and points that do not.     I thought I would use the bdist.tiles() function and keep only points where bdist>0.

I realize there can be issues with rounding distances, but I came across a situation where there seems to be a bug or an ambiguity for this function.  I have posted an example jpeg at http://mudrak.public.iastate.edu/bdist.tiles_problem.jpg that shows my tessellation, with bdist.tiles values plotted at the point location, and non-boundary tiles (bdist>0) printed in blue. There is a tile on the right that should be a boundary tile but has a bdist of 0.0269, which is larger than many of the other interior tiles.

** Is there a fix for this bug, or another way to identify boundary tiles? **

Thank you for any suggestions.

Erika Mudrak

------------------------------------------------------
Erika Mudrak
Postdoctoral Researcher
Ecology, Evolution, and Organismal Biology
251 Bessey Hall (mail)
224 Bessey Hall (office)
Iowa State University
Ames, IA 50011
mudrak@iastate.edu<mailto:mudrak@iastate.edu>
mudrak.public.iastate.edu


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