[postgis-users]postgis database connection failed.

[strk at refractions.net]

The upcoming GEOS 3.0.0rc1 implements your "wrapping" internally.
You can give it a try by installing the svn snapshot:
http://geos.refractions.net/geos-svn.tar.bz2

--strk;

On Fri, Aug 04, 2006 at 10:33:46AM +0200, Rene Neidt wrote:
> Hi all ...,
> 
> 
> We are creating an application with height requirements for geometric /
> geographical functions. We decided to use postgres/postgis:
> 	
> version(): "PostgreSQL 8.1.2 on i686-pc-mingw32, compiled by GCC gcc.exe
> (GCC) 3.4.2 (mingw-special)"
> gostgis_version(): "1.1 USE_GEOS=1 USE_PROJ=1 USE_STATS=1"
> 
> The features are really great and the performance is ok. But again we have
> trouble with the geos - functions (GEOS Intersection() threw an error! (or
> union or difference)). The reason seems to be a little inaccuracy in the
> coordinates, that accures while converting, intersecting, ... the
> geometries. For demonstration following example:
> 	
> Geometry1: GeometryFromText('MULTIPOLYGON(((5415144.13 5665163.17,5415155.58
> 5665159.46,5415167.78 5665155.72,5415173.02 5665153.58,5415185.57
> 5665172.69,5415167.07 5665187.86,5415157.12 5665174.96,5415144.13
> 5665163.17)))')
> 
> Geometry2:
> '010300000001000000150000006C9BD9273DA854411F2D0B86619C55412913FA603DA854413
> 78478B7619C5541B5075B743DA85441F4B287B1619C5541BE0C12833DA8544136D767BE619C5
> 5414C0D12833DA85441CCD767BE619C5541BA0D12833DA854417AD867BE619C5541F80D12833
> DA854411AD967BE619C5541000000F03FA854419A9999F9609C554114AE474141A8544152B81
> E65609C55411A0BD67443A85441398640BF639C55410CF5E3B843A854416D104AB2639C55415
> 982C67641A854416FFEFC41609C5541E9DFDF6E41A85441E8183538609C55414FBD366541A85
> 441AAF62830609C5541958E2A5A41A854410B1B282A609C5541D77B284E41A854411BD76D266
> 09C5541BB2AA74141A854418EFF1E25609C5541282A223541A85441D3804826609C55416D2D1
> 52941A8544164DFDE29609C5541560666DC3FA85441B3E0BCB1609C55416C9BD9273DA854411
> F2D0B86619C5541'
> 
> (Sorry for the complex geometries, but with Polygon((1 0, 0 1, 1 1, 1 0))...
> the problems do not occur.)
> 	
> select intersection(Gemetry1, Geometry2) 
> ->raises the error: 
> NOTICE:  TopologyException: no outgoing dirEdge found
> (5.41516e+006,5.66516e+006,5.66516e+006)
> GEOS Intersection() threw an error!
> 
> BUT
> 
> select intersection(Gemetry1, asText(Geometry2)) 
> -> works fine!
> 
> 
> Probably because of converting the geometry the coordinates are a little bit
> different, so that the error does not occur.
> 
> The last tip we got, was allways to use SnapToGrid. But we can not do. To
> demonstrate this, the two pictures:
> 	
> Input: We have the red polygon and the blue line. Both are "snaped to the
> grid". We want to devide the polygon into two parts by "cutting it with the
> line" (in our application we do not cut with a line, we use a polygon which
> overlays one part of the red polygon, so we can use intersection and
> difference...). 
> 
> The output of such a division would be the two green polygons (output.gif),
> which are allready snapped to grid (We have to snap them too, because maybe
> in the next moment one of them will be devided again...). And when we
> compare the union of both green polygons with the red polygon, it will not
> be the same. And so we will get holes (many of the red polygons adjoin each
> other an form a big polygon, which should not have holes...)
> 	
> I hope, you could understand, what we meant...
> 
> 
> So at the moment our workaround is to encapsulate the geos - functions. At
> first we try a intersection(geometry1, geometry2). If this raises an
> exception, we try intersection(asText(geometry1), asText(geometry2)). In the
> cases we had up to now it worked, but I am not sure, whether it will allways
> work...
> 
> In our opinion it is necessary to have a tollerance for the geos -
> functions, which could be set as a parameter.
> 
> Thank you in advance,
> Thomas and Rene
> 
>   



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