[postgis-devel] distance measuring between ugly polygons

[nicklas.aven at jordogskog.no]

As written in ticket #63 and #137 I have rewritten the oplygon-polygon measuring.
 
Here I post a shapefile with one ugly polygon and one more normal.
I don't know how common problem it is to work with this ugly ones, but I had to do it the other day and this will help me a lot.
 
 
if I run :
 
select st_distance(a.the_geom, b.the_geom) from example a, example b where a.objektid = 1 and b.objektid =2
 
I now get a querytime on about 720 ms to compare with more than 6 seconds before.
 
 
I also tried to use the bounding-box as a shortcircuit to determine if the polygons shared bbox and otherwise go directly on just comparing outer-rings. But that wasn't that easy as I understood it when the headers for handling the bboxes is in the postgis folder. But I don't tkink this way of doing it seems to be that much heavier. 
 
 
 
 
Something interesting to note is that I tried this polygon on an old Arcview 3.2 installation and that is fast, very, very fast. 
I don't understand how they did it and I doubt that arcgis of today can compare. But I had one test where I had a different result in Arcview and I think I could prove that postgis was right and Arcview wrong, so maybe they are taking som shortcircuit to much.
 
to try in arcview 3.x just run an avenue-script like:
Script.The.SetNumberFormat( "d.ddddd" )
vyn = av.finddoc("view1")
temat = vyn.findtheme("example.shp")
ftabben = temat.getftab
shpfld = ftabben.findfield("shape")
thedist = ftabben.returnvalue(shpfld,0).distance(ftabben.returnvalue(shpfld,1))
msgbox.info(thedist.asstring,"")
 
Greetings
Nicklas
 
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