Sounds good, Michael. If this proves out it would be worth a blog post by
you and/or me. (With a picture or two, of course!)
On Mon, Dec 2, 2013 at 6:07 PM, Michael Bedward
<[email protected]>wrote:
> That sounds like it could be just the ticket Martin !
>
> Thanks so much. I'll play with that and let you know how I get on.
>
> Michael
>
>
> On 3 December 2013 12:36, Martin Davis <[email protected]> wrote:
> > I just realized that you don't even have to alter STRtree to support a
> > custom filter function. STRtree already provides a method which accepts
> a
> > custom ItemDistance function. This could be given an implementation
> which
> > forces the distance of objects *not* in the current compass slice to be
> > Double.MAX_VALUE.
> >
> >
> > On Mon, Dec 2, 2013 at 5:25 PM, Martin Davis <[email protected]> wrote:
> >>
> >> A fascinating problem, Michael.
> >>
> >> How's this for a idea: use a direction-constrained nearest neighbour
> >> search. (Don't bother googling this - I just made it up!). The STRtree
> in
> >> JTS provides a nearest-neighbour search made efficient by walking the
> R-tree
> >> node hierarchy. It should be possible to add some further logic to the
> >> search algorithm to reject candidates which do not lie in the compass
> >> direction of interest. (It seems like it will be straightforward to
> compute
> >> whether a candidate lies with the compass slice).
> >>
> >> You'll have to open up the STRtree nearest neighbour code and add
> >> provision for a custom filter to be run on each candidate as they are
> added
> >> to the current search list. This should be built using a filter
> function
> >> interface, to make it reusable.
> >>
> >>
> >> On Mon, Dec 2, 2013 at 4:21 PM, Michael Bedward
> >> <[email protected]> wrote:
> >>>
> >>> Hi Martin,
> >>>
> >>> The following is a general algorithm query rather than a specific JTS
> >>> question - hope that's ok.
> >>>
> >>> I have a set of polygons which represent urban areas within a
> >>> fire-prone landscape. There are about 5000 polygons varying widely in
> >>> area, spatial extent, number of vertices and boundary complexity.
> >>>
> >>> I have the task of creating a regular grid of sample points within the
> >>> surrounding landscape and, for each point, determining the distance to
> >>> the nearest polygon within each of eight compass segments (ie. N to
> >>> NE, NE to E...). The results only need to be expressed as categorized
> >>> values based on a small number of distance cut-points.
> >>>
> >>> I've been trying to nut out something other than a brute force
> >>> approach to this without much success so far. One of the possibly less
> >>> brutish approaches I've thought of involves the following:
> >>>
> >>> 1. Split up the urban polygons by intersecting them with a regular
> >>> lattice, create PreparedGeometry objects for the resulting parts and
> >>> put them into an STRtree.
> >>>
> >>> 2. Construct a sampling template made up of polygons representing the
> >>> compass segments, each split according to the distance cut-points
> >>> (looking a bit like a dart board), possibly using a custom
> >>> CoordinateSequence to have vertex coordinates calculated on the fly
> >>> based on the centre coordinate.
> >>>
> >>> 3. For each sample point location:
> >>> For each compass segment:
> >>> For inner to outer segment part:
> >>> Query the spatial index with the segment part envelope
> >>> and, if any urban polygons are returned, test for
> >>> intersection.
> >>>
> >>> I'm sure there must be a better way. Any suggestions or comments will
> >>> be gratefully accepted.
> >>>
> >>> Michael
> >>>
> >>>
> >>>
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> >>
> >
>
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