[postgis-devel] [PostGIS] #231: New distance-calculations proposal

[PostGIS]

#231: New distance-calculations proposal
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  Reporter:  nicklas      |       Owner:  robe         
      Type:  enhancement  |      Status:  assigned     
  Priority:  medium       |   Milestone:  postgis 1.5.0
 Component:  postgis      |     Version:               
Resolution:               |    Keywords:               
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Comment (by nicklas):

 Great

 One thing to check is if we should use the old calculations for smaller
 geometries. I guess maybe my function gives more overhead-cost than gain.
 It also would be very easy to put in a rule where for instance npoints og
 geom1 * npoints of geom2 is more than 500 or something like that otherwise
 it just uses the old one.
 The real gain is big geometries far from eachother. Then I have had cases
 where the querytime reduses from 220000ms to jus about 2000 ms. Try the
 queries at your slide 19 you mentioned, Regina. I think the querytime is
 reduced by approx 90% at least eat some of them :-)

 Now I'm working on a proposal for better handling of subgeoms. There is
 two good things about it. First, of course it will reduce querytime when
 there is many subgeoms involved in the geometries. st_distance(alaska,
 texas) in Reginas dataset takes about 7 seconds with my patch, but with
 this subgeoms handling it is under 1 sec.

 But the other nice thing about it, is that it's usable innearest neighbour
 queries. just collect all geometries and get the closest point with
 st_shortestline. Then st_shortestline first arrange all incomming
 geometries like it would have been just any subgeoms. find the closest one
 and returns a line to the closest point of it.

 I think it's a good thing. I have it running for st_shortestline and
 st_distance but I have to modifie it to also take st_max_distance and
 st_longestline.

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Ticket URL: <http://trac.osgeo.org/postgis/ticket/231#comment:5>
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