[postgis-users] AsSVG inner poly reversed

[klaus Förster]

hi Sean,

does this occur when you use AsText() as well or is it limited to 
AsSVG()? are you using the latest PostGIS version? AsSVG(the_geom,0,8) 
seems to be the notation for an old version where precision was 
specified by number of significant digits and there some other bugs in 
this version as well.
Could you give an example with the original inner ring? you're using 
"..." to indicate you ommit some coords and the inner ring presented 
here is 4 units wide so it's hard to visually figure out direction with 
marker-symbols.
i think it's not true that in the first poly "the inner path is returned 
in the same direction as the out polygon." outer and inner path have to 
follow different directions to create a hole in SVG.

klaus

Sean M. Montague wrote:
> In my efforts to try and narrow my problem down and simplify my examples
> of some intersection problems, I've run across another oddity.  PostGIS
> is returning the inner polygon AsSVG of an intersection in reverse order
> to the outer polygon, causing display problems.  The inner polygon
> should be a hole, and when returned properly, have no fill.  Below are
> two sets of sql statements from my PHP code.    The first is just the
> poly "One" from table "test_02".  The SVG is below that.  This displays
> properly because the inner path is returned in the same direction as the
> out polygon.
> 
> $sql = ("SELECT  AsSVG(the_geom,0,8) As the_geom
> 	From test_02
> 	WHERE Name='One'");
> 
> --The outer polygon coords follow the first M, and the inner follows the
> second M.  I added comas and deleted the cords between the first 4 and
> last 4 for simplicity purposes.  These are in the correct order.
> 
> (outer)M -358 -4857 2866 -4235 3090 -2614 5520 -89 3969 4284 -651 4605
> -4978 2965 -5719 -1842 -2978 -4556 -358 -4857
> (inner)M 2083 -447, 2082 -497, 2081 -548, 2079 -598, ... 2079 -295, 2081
> -346, 2082 -396, 2083 -447
> 
> --This is how it would look normally.
> 
> M -358 -4857 2866 -4235 3090 -2614 5520 -89 3969 4284 -651 4605 -4978
> 2965 -5719 -1842 -2978 -4556 -358 -4857 M 2083 -447 2082 -497 2081 -548
> 2079 -598 ... 2079 -295 2081 -346 2082 -396 2083 -447
> 
> 
> The second is the intersection between the_geom from table "test_02" and
> a poly defined by the coordinates $theXMax and so on.
> 
> $theXMax= 5651;
> $theYMax= 5009;
> $theXMin=-6072;
> $theYMin= -4732;
> 
> $sql = ("SELECT  AsSVG(intersection(the_geom,
> PolygonFromText('POLYGON(($theXMin $theYMax, $theXMax $theYMax, $theXMax
> $theYMin, $theXMin $theYMin, $theXMin $theYMax))',32767)),0,8)
> 	As the_geom
> 	From test_02
> 	WHERE Name='One'
> 	AND the_geom && PolygonFromText('POLYGON(($theXMin $theYMax,
> $theXMax 	$theYMax, $theXMax $theYMin, $theXMin $theYMin, $theXMin
> $theYMax))',32767)");
> 
> --Notice that the inner poly cords are reversed.  This causes display
> problems.  The inner poly has a fill when it should not.
> 
> (outer)M -358 -4857 2866 -4235 3090 -2614 5520 -89 3969 4284 -651 4605
> -4978 2965 -5719 -1842 -2978 -4556 -358 -4857
> (inner)M 2083 -447, 2082 -396, 2081 -346, 2079 -295, ... 2079 -598, 2081
> -548, 2082 -497, 2083 -447
> 
> Any insight would be appreciated.
> 
> 
> 
> 
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