[postgis-users] Postgis Simplify

[strk at refractions.net]

Christo, please be specific about your problem.
Do you have a test case showing unexpected behaviour for
the simplify() function ?
Would you include postgis version information in the
file ?

--strk;

On Tue, Jul 26, 2005 at 09:27:44PM +0200, Christo Du Preez wrote:
> I used another installation, this time Linux and did the same test.
> 
> This time the result was different on rows 3, 6 and 9. More what I was 
> expecting in the first place.
> 
> 1:   25290 :  39
> 2:   23978 :  43
> 3:   25999 :  41
> 4:   4996  :  19
> 5:   24679  : 31
> 6:   50819 :  25
> 7:   31899 :  71
> 8:   63292 :  45
> 9:   84990 :  59
> 10: 12878 :  15
> 11: 1047   :   8
> 
> In previous posts I also mentioned the exponential format that my result 
> was, doing a Simplify(). I have also noticed that the exponential format 
> was only on rows 3, 6 and 9. The rest of the results was lat/long wgs84, 
> as expected.
> 
> Can someone please shed some light on this?
> 
> 
> strk at refractions.net wrote:
> 
> >Christo, nothing weird about it, not every shape contains redundand
> >informations.
> >
> >Consider a straight line defined by millions of intermediate points.
> >A simplify(geom, 0) would make it a 2 point line.
> >
> >If you google for Douglas-Peuker you'll get
> >lots of informations about the algorithm.
> >
> >--strk;
> >
> >On Mon, Jul 25, 2005 at 10:20:23PM +0200, Christo Du Preez wrote:
> > 
> >
> >>This is really weird.
> >>
> >>select npoints(the_geom), npoints(Simplify(the_geom, .1))
> >>from province
> >>
> >>results to:
> >>
> >>1:	25290,		39
> >>2:	23978,		43
> >>3:	25999,		22046
> >>4:	4996,		19
> >>5:	24679,		31
> >>6:	50819,		43120
> >>7:	31899,		71
> >>8:	63292,		45
> >>9:	84990,		70460
> >>10:	12878,		15
> >>11:	1047,		8
> >>
> >>The data is lat/long wgs84, what could cause rows 3,6 and 9 not to 
> >>simplify as much as the others?
> >>
> >>_______________________________________________
> >>postgis-users mailing list
> >>postgis-users at postgis.refractions.net
> >>http://postgis.refractions.net/mailman/listinfo/postgis-users
> >>   
> >>
> >_______________________________________________
> >postgis-users mailing list
> >postgis-users at postgis.refractions.net
> >http://postgis.refractions.net/mailman/listinfo/postgis-users
> >
> >
> > 
> >
> 
> -- 
> Kind Regards,
> Christo Du Preez
> 
> Senior Software Engineer
> Mecola IT
> http://www.mecola.com
> +27 [0]82 4255 895
> 
> _______________________________________________
> postgis-users mailing list
> postgis-users at postgis.refractions.net
> http://postgis.refractions.net/mailman/listinfo/postgis-users