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
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Technical Editor ANZJS
Department of Statistics
University of Auckland
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