Hi, I just want to add a possible solution to the problem in the special case
all the points must stay on the edge of the outline. THis is sometimes the
case when doing image analysis and you want to order the points along a
closed path.
In this specific case, you can use some algorithm like the tr
Thanks for the interesting reference to alphahull. It might be a good
starting point for placing e.g. a legend in a plot (I think the usual
techniques for this (gregmisc?) are a bit more brute-force.)
baptiste
2009/11/27 Kjetil Halvorsen :
> There is a package on CRAN implementing such an idea:
There is a package on CRAN implementing such an idea:
alphahull, phull is other package,
kjetil
On Thu, Nov 26, 2009 at 6:11 PM, baptiste auguie
wrote:
> 2009/11/26 Ted Harding :
>> Raising a rather general question here.
>>
>> This is a tantalising discussion, but the notion of "concave hull"
>
On Thu, Nov 26, 2009 at 9:45 PM, Ted Harding
wrote:
> So it is still an undefined solution. As is yours -- since you might
> want to use different radii of spheres from different directions.
I think the formal and rigorous definition is "a nice polygon that goes round
my points".
Barry
__
On 26-Nov-09 21:11:02, baptiste auguie wrote:
> 2009/11/26 Ted Harding :
>> Raising a rather general question here.
>>
>> This is a tantalising discussion, but the notion of "concave hull"
>> strikes me as extremely ill-defined!
>>
>> I'd like to see statement of what it is (generically) supposed t
2009/11/26 Ted Harding :
> Raising a rather general question here.
>
> This is a tantalising discussion, but the notion of "concave hull"
> strikes me as extremely ill-defined!
>
> I'd like to see statement of what it is (generically) supposed to be.
I'm curious too, but I can imagine the followin
Raising a rather general question here.
This is a tantalising discussion, but the notion of "concave hull"
strikes me as extremely ill-defined!
I'd like to see statement of what it is (generically) supposed to be.
The examples discussed so far seem to rely on a person's inner
feelings of what it
On 26/11/2009 4:02 AM, Corrado Topi wrote:
Dear David and other concave-hull-ists,
yes, I meant concave hulls indeed. I know about the algorithm mentioed
(www.concavehull.com) but it is not open source, so you cannot integrate it
in R, and it is apparently patented, so even if you find the des
Dear David and other concave-hull-ists,
yes, I meant concave hulls indeed. I know about the algorithm mentioed
(www.concavehull.com) but it is not open source, so you cannot integrate it
in R, and it is apparently patented, so even if you find the description
you cannot apply it to implement a
On Nov 25, 2009, at 7:51 PM, David Winsemius wrote:
Drats; Forgot the plot:
xx <- runif(100, -1, 1)
yy <- abs(xx)+rnorm(100,0,.2); plot(xx,yy, xlim=c( min(xx)-sd(xx),
max(xx)+sd(xx)), ylim =c( min(yy)-sd(yy), max(yy)+sd(yy)))
dens2 <- kde2d(xx, yy, lims=c(min(xx)-sd(xx), max(xx)+sd(xx),
Drats; Forgot the plot:
xx <- runif(100, 0, 1)
xx <- runif(100, -1, 1)
yy <- abs(xx)+rnorm(100,0,.2); plot(xx,yy, xlim=c( min(xx)-sd(xx),
max(xx)+sd(xx)), ylim =c( min(yy)-sd(yy), max(yy)+sd(yy)))
dens2 <- kde2d(xx, yy, lims=c(min(xx)-sd(xx), max(xx)+sd(xx), min(yy)-
sd(yy), max(yy)+sd(yy)
This is not a true convave hull, but a 2D density is something similar
and perhaps more "statistical":
library(MASS)
xx <- runif(100, 0, 1)
xx <- runif(100, -1, 1)
yy <- abs(xx)+rnorm(100,0,.2)
dens2 <- kde2d(xx, yy, lims=c(min(xx)-sd(xx), max(xx)+sd(xx),
min(yy)-sd(yy), max(yy)+sd(yy) )
Oh right I think I did not catch that *because of* the caps. Sorry.
r
-
Remko Duursma
Post-Doctoral Fellow
Centre for Plants and the Environment
University of Western Sydney
Hawkesbury Campus
Richmond NSW 2753
Dept of Biological Science
Macqua
On Wed, Nov 25, 2009 at 11:39 PM, Remko Duursma wrote:
> See the function 'convhulln' in the 'geometry' package. It uses this
> algorithm : http://www.qhull.org/
That looks like a CONVEX hull, the original poster asked about
CONCAVE hulls (and in all CAPS to emphasise this!).
I've seen various
See the function 'convhulln' in the 'geometry' package. It uses this
algorithm : http://www.qhull.org/
remko
-
Remko Duursma
Post-Doctoral Fellow
Centre for Plants and the Environment
University of Western Sydney
Hawkesbury Campus
Richmond NSW 27
Dear friends,
Do you know how to calculate the CONCAVE hull of a set of points (2-
dimensional or n-dimensional)? is that possible in R? (With a "smoothing"
parameter of course).
Best,
--
Corrado Topi
Global Climate Change & Biodiversity Indicators
Area 18,Department of Biology
University of Y
follow-up there would be
a reasonable next step?
--
David Winsemius
On Jan 20, 2009, at 6:37 PM, Charles Geyer wrote:
Message: 64
Date: Mon, 19 Jan 2009 15:14:34 -0700
From: Greg Snow
Subject: Re: [R] Concave Hull
To: Michael Kubovy , r-help
Message-ID:
Content-Type: text
cted that one of the r-sig-Geo
folks would have a ready answer. Perhaps a follow-up there would be a
reasonable next step?
--
David Winsemius
On Jan 20, 2009, at 6:37 PM, Charles Geyer wrote:
Message: 64
Date: Mon, 19 Jan 2009 15:14:34 -0700
From: Greg Snow
Subject: Re: [R] Concave Hu
> Message: 64
> Date: Mon, 19 Jan 2009 15:14:34 -0700
> From: Greg Snow
> Subject: Re: [R] Concave Hull
> To: Michael Kubovy , r-help
>
> Message-ID:
>
> Content-Type: text/plain; charset="us-ascii"
>
> I don't know if it is the
gt; From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-
> project.org] On Behalf Of Michael Kubovy
> Sent: Saturday, January 17, 2009 9:49 AM
> To: r-help
> Subject: [R] Concave Hull
>
> Dear Friends,
>
> Here is an algorithm for finding concave hulls:
>
Dear Friends,
Here is an algorithm for finding concave hulls: http://get.dsi.uminho.pt/local/
Has anyone implemented such an algorithm in R?
RSiteSearch('concave hull') didn't reveal one (I think).
_
Professor Michael Kubovy
University of Virginia
Department of Psych
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