[OGRUG] R-UG-Ottawa Digest, Vol 35, Issue 2

[John Lewis]

Hi,
After quickly reading your email it appears to me that you have three or
four separate problems to solve with the need in each  for different
spatial algorithms. In some ways you might be better off looking at GRASS
or Qgis to do this job.
I am travelling now so when I get settled on Thursday I'll look at what you
have written more carefully and see if I can help.
Maybe in the meantime someone else might come up with a workable solution
for you.
Cheers,
John Lewis

On Tue, Oct 28, 2014 at 7:00 AM, <r-ug-ottawa-request at r-project.org> wrote:

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> Today's Topics:
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>    1. What R packages/vocabulary do I need to search for Spatial
>       Distance ranking? (Daniel Buijs)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Mon, 27 Oct 2014 11:11:53 -0400
> From: Daniel Buijs <dbuijs at gmail.com>
> To: "r-ug-ottawa at r-project.org" <r-ug-ottawa at r-project.org>
> Subject: [OGRUG] What R packages/vocabulary do I need to search for
>         Spatial Distance ranking?
> Message-ID:
>         <CAFVA2r+ro0GN=
> rCqnkJ2UxJZ-CChTNMfRSR_-c9n5ofR5ZRVZw at mail.gmail.com>
> Content-Type: text/plain; charset="UTF-8"
>
> Hello,
>
> I'm trying to do something that I'm pretty sure can be done in R and
> probably has been done in R, but I'm having trouble finding the right
> search vocabulary to find appropriate packages.
>
> Briefly, I'm working with various spatial datasets available from
> data.ottawa.ca. I can import them into R with the rgdal package and I've
> gained some comfort with basic plotting and geometry operations with ggmap,
> sp and rgeos packages. What I'm after is the following:
>
> >From a set of Spatial features (including SpatialPoints, SpatialLines, and
> SpatialPolygons), I would like to assign arbitrary weights to features
> based on categorical variables in the data (i.e. 1 for schools, 2 for
> parks, -1 for highways, etc.) and then estimate an intensity/density
> surface at defined points (like road intersections). I think that this will
> let me answer questions like "what are the top 10 intersections that are
> closest to schools, parks (weight 2 because I care more about parks than
> schools) and furthest form highways?"
>
> I don't really care about the actual value, I'm just using it as a ranking
> score.
>
> I think some flavour of 2D kernel density estimation will do this. This
> particular problem seems to differ from the more simple examples given in
> the various package vignettes in the following ways:
>
> To deal with roads in the form of SpatialLines, I either need to sample
> them into points with a fixed absolute frequently that results in a
> steady-state maximum equivalent to the maximum of a weight=1 point source,
> or find a package that has some reasonable treatment of edge effects.
>
> SpatialPolygons (i.e. large areas like parks) should have a uniform
> weighting of 1 within the polygon and behave like a SpatialLine at the
> edges. Weighted points within the polygon should combine constructively
> with the base weight of the polygon. If I have to do this with sampling, as
> with the SpatialLines, ok. Using the centroid is a temporary solution for
> smallish areas, but for bigger or irregular shapes, would prefer to deal
> with the SpatialPolygon as is and/or with somewhat automatic sampling to
> points.
>
> To estimate the intensity/density function at arbitrary points (i.e.
> intersections), I probably need to estimate the whole surface function with
> regular spacing and then interpolate from the estimated surface (somewhat
> concerned about double-sampling error in this case). Would prefer an
> algorithm that could calculate estimates directly from the points I care
> about for ranking.
>
> I haven't seen any packages yet that look like they would be comfortable
> with negative weights (i.e. things I don't want to be close to).
>
> I need to have some global control/parameter that allows me to adjust
> either the bandwidth of the smoothing and/or the extinction coefficient of
> the kernel function so I can empirically dictate and experiment with
> distance effects (i.e. objects more than x km away shouldn't influence the
> value function at my point of interest).
>
> Any thoughts on recommended reading/R packages that either already provide
> this functionality or could be extended to do this kind of thing?
>
> Dan Buijs
>
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>
>
>
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> End of R-UG-Ottawa Digest, Vol 35, Issue 2
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