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Posted to dev@lucene.apache.org by "John Berryman (JIRA)" <ji...@apache.org> on 2013/05/09 09:01:20 UTC
[jira] [Comment Edited] (LUCENE-4922) A SpatialPrefixTree based on
the Hilbert Curve and variable grid sizes
[ https://issues.apache.org/jira/browse/LUCENE-4922?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13652785#comment-13652785 ]
John Berryman edited comment on LUCENE-4922 at 5/9/13 6:59 AM:
---------------------------------------------------------------
{{
# Converts from an x,y coordinate (vals[0],vals[1]) between min and max values to a point on the Hilbert curve in base4
#
def hilbert_point(vals,depth,mins=[],maxs=[]):
"""
cell_names
3 2
0 1
"""
if(mins):
# then convert vals to some place in 1-by-1 grid at the origin
vals[0] = (vals[0]-mins[0])/(maxs[0]-mins[0])
vals[1] = (vals[1]-mins[1])/(maxs[1]-mins[1])
if(depth == 0):
return ''
if( vals[0]<=0.5 and vals[1]<=0.5 ):
cell_name = '0'
x = vals[1]*2
y = vals[0]*2
elif( vals[0]>=0.5 and vals[1]<=0.5 ):
cell_name = '1'
x = (vals[0] - 0.5)*2
y = vals[1]*2
elif( vals[0]>=0.5 and vals[1]>=0.5 ):
cell_name = '2'
x = (vals[0] - 0.5)*2
y = (vals[1] - 0.5)*2
elif( vals[0]<=0.5 and vals[1]>=0.5 ):
cell_name = '3'
x = 1 - (vals[1] - 0.5)*2
y = 1 - vals[0]*2
return cell_name + hilbert_point([x,y],depth-1)
}}
was (Author: berryman):
# Converts from an x,y coordinate (vals[0],vals[1]) between min and max values to a point on the Hilbert curve in base4
#
def hilbert_point(vals,depth,mins=[],maxs=[]):
"""
cell_names
3 2
0 1
"""
if(mins):
# then convert vals to some place in 1-by-1 grid at the origin
vals[0] = (vals[0]-mins[0])/(maxs[0]-mins[0])
vals[1] = (vals[1]-mins[1])/(maxs[1]-mins[1])
if(depth == 0):
return ''
if( vals[0]<=0.5 and vals[1]<=0.5 ):
cell_name = '0'
x = vals[1]*2
y = vals[0]*2
elif( vals[0]>=0.5 and vals[1]<=0.5 ):
cell_name = '1'
x = (vals[0] - 0.5)*2
y = vals[1]*2
elif( vals[0]>=0.5 and vals[1]>=0.5 ):
cell_name = '2'
x = (vals[0] - 0.5)*2
y = (vals[1] - 0.5)*2
elif( vals[0]<=0.5 and vals[1]>=0.5 ):
cell_name = '3'
x = 1 - (vals[1] - 0.5)*2
y = 1 - vals[0]*2
return cell_name + hilbert_point([x,y],depth-1)
> A SpatialPrefixTree based on the Hilbert Curve and variable grid sizes
> ----------------------------------------------------------------------
>
> Key: LUCENE-4922
> URL: https://issues.apache.org/jira/browse/LUCENE-4922
> Project: Lucene - Core
> Issue Type: New Feature
> Components: modules/spatial
> Reporter: David Smiley
> Assignee: David Smiley
> Labels: gsoc2013, mentor, newdev
>
> My wish-list for an ideal SpatialPrefixTree has these properties:
> * Hilbert Curve ordering
> * Variable grid size per level (ex: 256 at the top, 64 at the bottom, 16 for all in-between)
> * Compact binary encoding (so-called "Morton number")
> * Works for geodetic (i.e. lat & lon) and non-geodetic
> Some bonus wishes for use in geospatial:
> * Use an equal-area projection such that each cell has an equal area to all others at the same level.
> * When advancing a grid level, if a cell's width is less than half its height. then divide it as 4 vertically stacked instead of 2 by 2. The point is to avoid super-skinny cells which occurs towards the poles and degrades performance.
> All of this requires some basic performance benchmarks to measure the effects of these characteristics.
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