I don't be sure use the CCW detection is what I'm need. Because my lines are surely simple, but not closed.
I need more study on the problem. 2010/5/3 strk <[email protected]> > You're probably looking for an ST_IsCCW() function > ( is counter-clock-wise ? ). > > Such a function could only work with closed and simple > lines (see ST_IsClosed and ST_IsSimple). > > It's not available at the moment, but defining the interface > is half work, so shouldn't cost too much to add :) > > --strk; > > () Free GIS & Flash consultant/developer > /\ http://strk.keybit.net/services.html > > On Sun, May 02, 2010 at 11:27:25AM +0200, Andrea Peri wrote: > > Hi, > > > > I do some test. > > > > I notice that the ST_OrderingEquals > > > > return true only when two lines are perfectly identical (same sequence > > vertex too). > > > > For example: > > > > Select ST_OrderingEquals( > > ST_GeomFromText('LINESTRING(2 3, 3 2, 6 1)',3003 > > ),ST_GeomFromText('LINESTRING(2 3, 3 2, 6 1)',3003 ) > > ) > > > > But if I add a single vertex to one of lines it return false. > > Select ST_OrderingEquals( > > ST_GeomFromText('LINESTRING(2 3, 3 2, 6 1, 8 9)',3003 > > ),ST_GeomFromText('LINESTRING(2 3, 3 2, 6 1)',3003 ) > > ) > > > > So it is not useful to detect the versus of lines because > > the linestring of the line table is not sure they are perfectly identical > to > > the definition of the boundary of polygons. > > The boundary of polygons are always closed lines. > > Instead the same closed arc may be require more lines of the line table. > > > > More again: > > even supposing the lines-table elements was closed like the boundary of > > polygons the ST_OderingEqual require they are > > first vertex identical. > > > > So this case of two lines identical, and same versus but different > starting > > vertex, return false. > > > > Select ST_OrderingEquals( > > ST_GeomFromText('LINESTRING(2 3, 3 2, 6 1, 8 9, 2 3)',3003 > > ),ST_GeomFromText('LINESTRING(3 2, 6 1, 8 9, 2 3, 3 2)',3003 ) > > ) > > > > Regards, > > > > > > -- > > ----------------- > > Andrea Peri > > . . . . . . . . . > > qwerty אטלעש > > ----------------- > > > _______________________________________________ > > postgis-users mailing list > > [email protected] > > http://postgis.refractions.net/mailman/listinfo/postgis-users > > -- ----------------- Andrea Peri . . . . . . . . . qwerty àèìòù -----------------
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