I just tried the following:
require(deldir)
require(geometry)
set.seed(42)
bm <- data.frame(x=sample(1:82,800,TRUE),y=sample(1:82,800,TRUE))
del <- deldir(bm)
tri <- triang.list(del)
geodel <- delaunayn(bm)
length(tri) # Got [1] 1481
dim(geodel) # Got [1] 1481 3
So all seems to be in harmony in the universe.
Something is weird about your "bm"; hard to say what without seeing it.
One thought: Are there any duplicated points in your "bm"? (Upon
re-reading your message and noting the problem with "ptNum", I think
this might be the case.)
Try doing something like:
newbm <- bm[!duplicated(bm),]
and then hit "newbm" with both deldir() and delaunayn().
cheers,
Rolf Turner
On 23/05/14 03:36, Raphael Päbst wrote:
Hello again,
I have found further depths of confusion concerning delaunay
triangulations to explore.
Here is the code I'm using to create the confusing results:
bm <- getbm(x) # a data.frame with 2 columns and 800 rows, values are
integers ranging from 1 to 82
del <- deldir(bm) # creating an object of type deldir with the 800
coordinates from bm
tri <- triang.list(del) # creating a list of length n, holding the n
triangles created by the delaunay triangulation with deldir(bm) as
data.frames
geodel <- delaunayn(bm) # creating a matrix with 3 columns and m rows
for the m triangles created by the delaunay triangulation using
delaunayn(bm) from geometry-package
now, the following is what I would expect: n and m should be the same,
since both triangulations should give me the same number of triangles,
right?
but this is what I get:
nrow(geodel) = 1584
length(tri) = 1186
This confuses me and I have the feeling I have left out some very
important parameter either in delaunayn() or deldir() to create the
different results.
There is however more confusion to come, this time in the result of
triang.list(del):
Every element in that list is a data.frame holding information on one
triangle. It has 3 columns and 3 rows with column headers 'ptNum', 'x'
and 'y'. Now I would expect, that 'ptNum' would give me the index at
which I can find the coordinates 'x' and 'y' as a row in my original
data.frame of coordinates, bm. And for example
bm[1,] gives me the same 'x' and 'y' that are listed in data.frame
tri[1] as 'ptNum' = 1.
But for some other points this does not work and for example the 'x'
and 'y' of 'ptNum' = 129 do not match bm[129, ]. Have I totally
misunderstood the meaning of 'ptNum' in this case or does my mistake
lie somewhere else?
Once again please excuse my slightly chaotic description of my
problems and my faulty english and thanks for any help you can give!
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