On Sun, Dec 8, 2013 at 3:43 PM, Michael Bedward
<[email protected]>wrote:
>
>
> > One potential issue I just thought of is that the STRtree NN algorithm
> > relies on the envelope-envelope distance being a "consistent proxy" with
> the
> > actual distance between the geometry and the query geometry (the point).
> > However, I think this is still the case with the Sector distance, so that
> > should be fine.
>
> Hmm... but if "consistent proxy for" means something like "has the
> same rank order as" won't there be a problem ?
>
"Consistent proxy" means that the item distance algorithm must be bounded
by the maximum and minimum Euclidean distances between the envelopes of the
items. This is to allow pruning of known dead branches during the tree
search.
I think the actual sector distance algorithm obeys this bound (the sector
distance is within the envelope distances). But I'm not sure about the idea
of returning a MAX_DOUBLE distance to prune geometries fully outside the
sector. It *might* work - but it might not. The first step is to set up a
simple test case and try it out. If this doesn't work, then will have to
think again about how to discard out-of-sector geometries.
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