[R-sig-Geo] [FORGED] Re: [FORGED] kernel density: units of bandwidth

Tadaishi Yatabe-Rodriguez tyatabe at ucdavis.edu
Mon Feb 22 22:58:23 CET 2016

Sorry, Rolf. I didn't realize I was replying only to you!
Thanks for your reply. I'll project before making the ppp object that I'll
use in my Kernel.



On Mon, Feb 22, 2016 at 1:53 PM, Rolf Turner <r.turner at auckland.ac.nz>

> On 23/02/16 10:34, Tadaishi Yatabe-Rodriguez wrote:
> Thanks, Rolf. This ,makes it clearer. I've another question though: the
>> ppp object I get the Kernel density from is not projected, then what
>> would be the unit of projection of this un-projected object? The
>> projection of the object from which it was created from (e.g.
>> SpatialPoints object)?
>> Thanks again,
> You should probably keep this discussion on-list; others who subscribe to
> the list are much more knowledgeable than I and may have useful
> contributions to make (and may correct my errors).  I have taken the
> liberty of including the list in my reply.
> I think that your question is not well-posed.  The density.ppm() function
> treats the coordinates of points as Euclidean coordinates (with the same
> units on both the x and y axes).  If your point pattern is "un-protected"
> then I presume that x and y are in longitude and latitude in which case the
> coordinates are not Euclidean and the x and y axis units are different,
> since longitude and latitude are constructed in different ways.
> If the region in question is "small" (and not too near either pole, I
> guess) then this probably doesn't make much difference, and the units of
> sigma would, roughly speaking, be "degrees".  Otherwise it seems to me
> there is no meaningful answer to your question.
> It would probably be best to project your data before forming the ppp
> object.
> Ege has been doing some work on point patterns on the sphere which might
> possibly be of relevance here.  He may feel like chiming in on this issue.
> cheers,
> Rolf
> --
> Technical Editor ANZJS
> Department of Statistics
> University of Auckland
> Phone: +64-9-373-7599 ext. 88276

*Tadaishi Yatabe*
Center for Animal Disease Modeling and Surveillance (CADMS)
Department of Medicine and Epidemiology
School of Veterinary Medicine
University of California Davis


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