[postgis-devel] RE: 40% faster st_distance and returning measurepoints :-)

[nicklas.aven at jordogskog.no]

Hi againI found that my modification crashed st_dwithin, but this version I think will work./NicklasDatum: 2009-03-11 13:46:35Från: nicklas.aven at jordogskog.noTill:Ämne: 40% faster st_distance and returning measurepoints :-)HalloI'm new to this list and have done my first steps in writing c-code. Thanks to the very well-written and readable source-code I think I have succeded over my expectations.What I have done is rewriting quite great parts of measures.c. My goal was to get the points out of st_distance from where the distance was calculated.The result was that st_distance worked about 40% faster on my small testmaterial. The points I wanted is also there, but I don't know the best way to output them.The idea I have followed is just to store the shortest distance and it's points in a new structure I have called DISTLINE.Then I only do testing if a diastance is closer then the "earlier shortest" in "distance2d_pt_pt" so there is no testing in the looping of the other relate!
 ted functions.I think the progress in speed should make it interesting for implementing but someone experienced have to take a serious look at it.I also would be greatful if I could get some help with the output of my points. they are included in the structure DISTLINE liketypedef struct{double d;  /*distance*/POINT2D *p1;  /*1st measure point*/POINT2D *p2; /*2nd measure point*/} DISTLINE;and they will be present when the process returns to function:lwgeom_mindistance2d_recursiveI attach my measure.c, libwgeom.h a small dataset with som roads in Norway and my resulting dllThe test I have done to compare speed is justselect a.vegnummer,b.vegnummer, st_distance(a.the_geom,b.the_geom) as avstand from distancetest a,distancetest b;on the attached dataset.My result was:original measure.cTotal query runtime: 3999 ms.400 rows retrieved.The new measure.cTotal query runtime: 2374 ms.400 rows retrieved.This increase in speed could be quite important on big "nearest neighbour" calcula!
 tions.I also mean som function like st_shortestline(geom1,geom2) would be nice and now the points for that line is ready to use.Have a nice dayfrom a quite proud beginnerNicklas Avén
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