[mapserver-users] Buffer

[Steve Lime]

It may not be an error in the buffer function. It could be an error in
MapServer's GEOS support, specifically
in the code that does the translation between GEOS geometries and
MapServer shapeObj's.

Can you try converting your WKT polygon to a shape and then back to
WKT? They should match, but if not
that could be the source of the error. Also, what version are we taking
about (GEOS and MapServer)?

Steve

>>> On 12/23/2008 at 4:46 AM, in message
<AEE643A9833AA34FA047EAE74820EB7F07C6C54A at lymbx1.COWI.Net>, "Jeppe
Lund
Andersen" <JXA at cowi.dk> wrote:
> Hello
> 
> Thank you for running the code
> 
> Okay there is an error in the buffer function.
> The reason why I have less vertices/segments is because I have
changed the 
> code to take a parameter to tell how many vertices/segments.
> 
> Jeppe
> 
> 
>> -----Original Message-----
>> From: José María Michia [mailto:jose.maria.michia at gmail.com] 
>> Sent: Tuesday, December 23, 2008 2:36 AM
>> To: Jeppe Lund Andersen
>> Cc: mapserver-users at lists.osgeo.org 
>> Subject: Re: [mapserver-users] Buffer
>> 
>> 2008/12/22 Jeppe Lund Andersen <JXA at cowi.dk>:
>> > Hello all
>> >
>> > I need a little help here
>> > If I run the following
>> >
>> > $NewShapeFromWkt = ms_shapeObjFromWkt( "MULTIPOLYGON(((566725.7595

>> > 6131923.3645, 566755.923 6131916.786, 566774.0885 6131912.417, 
>> > 566794.538 6131907.418, 566798.6035 6131901.309, 566788.164 
>> > 6131836.8625, 566779.4235 6131830.6935, 566724.0525 6131841.7915,

>> > 566723.665 6131863.507, 566714.6605 6131868.216, 566718.157 
>> > 6131885.2325, 566725.7595 6131923.3645)),
>> > ((566655.975 6131935.652, 566661.6235 6131937.282, 566696.924 
>> > 6131929.5735,
>> > 566694.755 6131919.4455, 566702.3 6131917.506, 566704.304 
>> 6131927.964,
>> > 566725.6935 6131923.2945, 566718.091 6131885.1625, 566652.446 
>> > 6131899.0795,
>> > 566655.975 6131935.652)))" );
>> >
>> > $new_shape = $NewShapeFromWkt->Buffer(-0.1); 
>> > echo($new_shape->toWkt());
>> >
>> > I get this shape, and it remove one of the shapes in the 
>> multipolygon 
>> > can any one try and see if they get the same error ?
>> >
>> > POLYGON ((566725.8376634185000000 6131923.2451023338000000, 
>> > 566755.9006510233700000 6131916.6885235561000000, 
>> > 566774.0649345762800000 6131912.3198161256000000, 
>> > 566794.4763613325800000 6131907.3301233519000000, 
>> > 566798.4985129962400000 6131901.2862604791000000, 
>> > 566788.0720058706400000 6131836.9199698064000000, 
>> > 566779.4009780341300000 6131830.8000029027000000, 
>> > 566724.1510484541100000 6131841.8737367792000000, 
>> > 566723.7649840826600000 6131863.5087841563000000, 
>> > 566723.7113416689700000 6131863.5956140496000000, 
>> > 566714.7736214522700000 6131868.2696908442000000, 
>> > 566718.2549535385300000 6131885.2123727966000000, 
>> > 566718.2550698703900000 6131885.2129474934000000, 
>> > 566725.8376634185000000 6131923.2451023338000000))
>> >
>> 
>> I execute your code, with its data, in my system, with the
following
>> results: One of the polygons has been eliminated, just like 
>> as in their case. In addition, my result, it has more 
>> vertices. In the attached image you can see the differences 
>> (or at least part of them).
>> I don't know which is the reason for the difference in 
>> resolution (number of vertices).
>> 
>> My result:
>> 
>> POLYGON ((566725.8376634184969589 6131923.2451023338362575,
>> 566755.9006510233739391 6131916.6885235561057925,
>> 566774.0649345762794837 6131912.3198161255568266,
>> 566794.4763613325776532 6131907.3301233518868685,
>> 566798.4985129962442443 6131901.2862604791298509,
>> 566788.0720058706356212 6131836.9199698064476252,
>> 566779.4009780341293663 6131830.8000029027462006,
>> 566724.1510484541067854 6131841.8737367792055011,
>> 566723.7649840826634318 6131863.5087841562926769,
>> 566723.7647452256642282 6131863.5141337206587195,
>> 566723.7642203503055498 6131863.5194628285244107,
>> 566723.7634109617210925 6131863.5247561996802688,
>> 566723.7623193806502968 6131863.5299986554309726,
>> 566723.7609487375011668 6131863.5351751623675227,
>> 566723.7593029623385519 6131863.5402708780020475,
>> 566723.7573867744067684 6131863.5452711889520288,
>> 566723.7552056685090065 6131863.5501617584377527,
>> 566723.7527658988256007 6131863.5549285616725683,
>> 566723.7500744614517316 6131863.5595579305663705, 
>> 566723.7471390739083290 6131863.5640365900471807,
>> 566723.7439681534888223 6131863.5683516971766949,
>> 566723.7405707928119227 6131863.5724908793345094,
>> 566723.7369567337445915 6131863.5764422677457333,
>> 566723.7331363394623622 6131863.5801945300772786,
>> 566723.7291205649962649 6131863.5837369086220860,
>> 566723.7249209255678579 6131863.5870592454448342,
>> 566723.7205494635272771 6131863.5901520121842623,
>> 566723.7160187140107155 6131863.5930063417181373,
>> 566723.7113416689680889 6131863.5956140495836735, 
>> 566714.7736214522738010 6131868.2696908442303538,
>> 566718.2549535385333002 6131885.2123727966099977,
>> 566718.2550698703853413 6131885.2129474934190512,
>> 566725.8376634184969589 6131923.2451023338362575))
>> 
>> Saludos
>> José María
>> 
>> 
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