[postgis-users] Postgis Simplify
Christo Du Preez
christo at mecola.com
Wed Jul 27 02:52:33 PDT 2005
Sorry, the 20 tolerance was a typo, it was actually 0.1
strk at refractions.net wrote:
>Christo, you are using two different versions of postgis:
>0.9.1 on Windows and 1.1.0CVS on Gentoo.
>If you want to help you need to provide a self-contained
>test script showing the problem.
>
>BTW, note that 20 is a *really* big number for a tolerance
>in lat/long space.
>
>--strk;
>
>On Wed, Jul 27, 2005 at 11:39:53AM +0200, Christo Du Preez wrote:
>
>
>>No I don't have a test case, the result on the Windows platform just
>>didn't look right to me.
>>
>>Windows:
>>
>>version: PostgreSQL 8.0.3 on i686-pc-mingw32, compiled by GCC gcc.exe
>>(GCC) 3.4.2 (mingw-special)
>>postgis_version: 0.9 USE_GEOS=1 USE_PROJ=1 USE_STATS=1
>>postgis_lib_version: 0.9.1
>>postgis_geos_version: 2.1.1
>>postgis_proj_version: Rel. 4.4.9, 29 Oct 2004
>>postgis_full_version: POSTGIS="0.9.1" GEOS="2.1.1" PROJ="Rel. 4.4.9,
>>29 Oct 2004" USE_STATS DBPROC="0.0.1" RELPROC="0.0.1"
>>
>>Gentoo:
>>
>>version: PostgreSQL 8.0.2 on i686-pc-linux-gnu, compiled by GCC gcc
>>(GCC) 3.3.2 20031218 (Gentoo Linux 3.3.2-r5, propolice-3.3-7)
>>postgis_version: 1.1 USE_GEOS=0 USE_PROJ=1 USE_STATS=1
>>postgis_lib_version: 1.1.0CVS
>>postgis_geos_version: 2.1.1
>>postgis_proj_version: Rel. 4.4.9, 29 Oct 2004
>>postgis_full_version: POSTGIS="1.1.0CVS" GEOS="2.1.1" PROJ="Rel.
>>4.4.9, 29 Oct 2004" USE_STATS DBPROC="0.3.0" RELPROC="0.3.0"
>>
>>At first I recieved an "NOTICE: IllegalArgumentException: Exponent out
>>of bounds" trying to run:
>>
>> SELECT
>>AsSVG(intersection(Simplify(the_geom,20),GeometryFromText('POLYGON((16
>>-38,33 -38,33 -21,16 -21,16 -38))',-1)),1,1) AS svg_geom
>> FROM province
>> WHERE the_geom && setSRID('BOX3D(16 -38, 33 -21)'::box3d,-1)
>>
>>It was the intersection() function that caused the error for whatever
>>reason. Then I stripped the intersection() function and and noticed the
>>exponential format of the results on windows (only on rows 3, 6 and 9),
>>but the results on linux was lat/long wgs84. After further testing I
>>noticed using npoints() that some rows on the windows machine didn't
>>simplify as much as on the linux box. Again this was only on rows 3, 6
>>and 9. As you can see below.
>>
>>windows:
>>
>>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
>>
>>linux
>>
>>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
>>
>>
>>strk at refractions.net wrote:
>>
>>
>>
>>>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?
>>>>>>
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>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
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>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>--
>>>>Kind Regards,
>>>>Christo Du Preez
>>>>
>>>>Senior Software Engineer
>>>>Mecola IT
>>>>http://www.mecola.com
>>>>+27 [0]82 4255 895
>>>>
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>>>>
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>>--
>>Kind Regards,
>>Christo Du Preez
>>
>>Senior Software Engineer
>>Mecola IT
>>http://www.mecola.com
>>+27 [0]82 4255 895
>>
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>>postgis-users mailing list
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>>http://postgis.refractions.net/mailman/listinfo/postgis-users
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--
Kind Regards,
Christo Du Preez
Senior Software Engineer
Mecola IT
http://www.mecola.com
+27 [0]82 4255 895
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