On Thu, Apr 9, 2009 at 9:30 AM, <[email protected]> wrote:
> On Thu, 9 Apr 2009 02:12:08 +0300, pablo platt <[email protected]> > wrote: > > Hi, > > > > I posted this question in the forum but I think that the list is more > > active. > > > > PostGIS uses R-Tree index over GIST. > > I'm trying to understand if it is possible to use couchDB for storing and > > indexing the osm data. > > couchdb is a schema less db for storing documents. Each document store > data > > encoded as JSON. > > It uses B-Tree index so the only way I know to enable spatial index is to > > use space-filling-curves (z-order, morton codes) > > to translate a lat,lng to a number and then index all the numbers using a > > B-Tree. > > From what I found out you usually do not use a Z-curve or Hilbert-Curve > on a 1-dimensional index but you use it while constructing a > never-to-be-changed > 2D-tree. > However I could not find any multi-dimensional trees that can do a > rebalancing > in O(1) like an AVL-tree can. I understand that you map 2D data on a 1D array and then you index it with a B-Tree. This article explains how it works http://www.ddj.com/184410998. It also says that R-Tree is always preferred but doesn't explains why. So while this may be a good index for data-sets that never change it > quickly > becomes highly unbalanced in datasets that are changed frequently. > > I guess an R-Tree (also called 2D (R)ange-tree) was just easiest with the > existing indexing datastructures they had and it provides adequate > performance. > > Marcus >
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