[postgis-devel] I want boxes

[Paragon Corporation]

Yes lets come up with a symbol we haven't used

<-#-> 

> -----Original Message-----
> From: postgis-devel-bounces at postgis.refractions.net 
> [mailto:postgis-devel-bounces at postgis.refractions.net] On 
> Behalf Of Paul Ramsey
> Sent: Tuesday, September 27, 2011 1:16 PM
> To: postgis-devel at postgis.refractions.net
> Subject: Re: [postgis-devel] I want boxes
> 
> What an exciting opportunity to try out strategy numbers... 
> through the magic of PostgreSQL's GiST framework, both 
> strategies can be made available using different operators 
> (because we love, love, love obscure combinations of symbols).
> 
> P.
> 
> On Tue, Sep 27, 2011 at 10:07 AM, Paragon Corporation 
> <lr at pcorp.us> wrote:
> > Paul,
> >
> > If it's not that much harder -- box is better even for 
> things that are 
> > closish.
> >
> > Take a road -- I can do tests to confirm but box is better 
> because I 
> > can never use the centroid
> >
> > Centroid tells me the closest is the farthest.  Not 
> terribly useful.  
> > At least the box will let me know it's useless.
> >
> > With centroid I have no idea if I'm dealing with largish or 
> smallish 
> > things to consider how credible the answer is.
> >
> >
> >
> >> -----Original Message-----
> >> From: Paul Ramsey [mailto:pramsey at opengeo.org]
> >> Sent: Tuesday, September 27, 2011 1:03 PM
> >> To: Paragon Corporation
> >> Cc: Sandro Santilli; nicklas.aven at jordogskog.no
> >> Subject: Re: I want boxes
> >>
> >> Just to point out:
> >>
> >> The problem with the centroid is that, for large long 
> features, lt's 
> >> overselective. So to get the "full potential set" of things you'll 
> >> have to winnow down, you need a large first limit.
> >>
> >> The problem with the box is that, for large long features, it's 
> >> underselective. So you'll get lots of things that aren't actually 
> >> very close still showing up al their boxes interact with the 
> >> candidate, causing zero-distance returns. The net result is that 
> >> you'll still need a large first limit, to ensure that in 
> addition to 
> >> all the zero-distance false positives you also have the non-zero 
> >> results that might actually be the closest.
> >>
> >> Which is not to say the box-distance might not be better 
> in the end, 
> >> just I'm finding in hard to visualize an extreme improvement.
> >>
> >> P.
> >>
> >> On Tue, Sep 27, 2011 at 9:57 AM, Paragon Corporation <lr at pcorp.us> 
> >> wrote:
> >> > If it weren't for the fact it's the centroid of the box, I
> >> would agree
> >> > with you.
> >> >
> >> > But honestly in many of my cases the centroid of my object
> >> is no where
> >> > near the centroid of the box so pretty useless to base
> >> anything on it.
> >> > Works fine for parcels but not much else I have.
> >> >
> >> > for the case of polygons etc.  as Nicklas and I think 
> others have 
> >> > pointed out, the objective is a little different
> >> >
> >> > not to get the best sort but faster compute the maximum
> >> distance you
> >> > need to stretch out to grab the top 10.
> >> >
> >> > Though I'm curious how Oracle's NN which is also imperfect works.
> >> > Haven't paid much attention to that.
> >> >
> >> > Thanks,
> >> > Regina
> >> >
> >> >
> >> >
> >> >> -----Original Message-----
> >> >> From: Paul Ramsey [mailto:pramsey at opengeo.org]
> >> >> Sent: Tuesday, September 27, 2011 12:52 PM
> >> >> To: Paragon Corporation
> >> >> Cc: Sandro Santilli; nicklas.aven at jordogskog.no
> >> >> Subject: Re: I want boxes
> >> >>
> >> >> I can almost guarantee you that boxes will be just as 
> bad but in a 
> >> >> different way... and centroids are always relative to 
> the box :) I 
> >> >> will think on doing box distance.
> >> >> P.
> >> >>
> >> >> On Tue, Sep 27, 2011 at 9:48 AM, Paragon Corporation 
> <lr at pcorp.us>
> >> >> wrote:
> >> >> > As I pointed out to strk -- the centroid appears to be
> >> ceontroid of
> >> >> > the box which is even less useful than I had originally
> >> >> thought.  That
> >> >> > said box distance is way better.
> >> >> >
> >> >> > Is it possible to have the distance be box based instead of
> >> >> centroid.
> >> >> > Centroid isn't terrible useful.
> >> >>
> >> >
> >> >
> >> >
> >>
> >
> >
> >
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