[Jts-topo-suite-user] question on isValidOp()

[John Cartwright - NOAA Federal]

Hello All,

I'm confused about the isValidOp.setSelfTouchingRingFormingHoleValid(true)
method. Given a bow-tie polygon like the one below, I would have expected
setting the above option to cause the polygon to report as valid but it
doesn't.
​

Can someone please clarify for me?

Thanks!

--john

​//​
​//JTS version 1.14.0 with Groovy 2.4.5.​
//
wkt = '''POLYGON((1 1, 2 1, 1 2, 2 2, 1 1))'''
def geom = wktReader.read(wkt)

def validOp = new IsValidOp(geom)
validOp.setSelfTouchingRingFormingHoleValid(true)

//fails
assert geom.valid

[Martin Davis]

That polygon contains two edges that cross, which is invalid under any
setting.

The setSelfTouchingRingFormingHoleValid parameter only allows situations
where a ring self *touches*, not crosses, AND only for the situation where
the self-touch forms a hole - NOT where it splits the polygon into two
separate areas.

So these are valid with the setSelfTouchingRingFormingHoleValid flag set:

Shell self-touches and isolates a hole:

POLYGON ((100 400, 300 400, 300 300, 150 350, 150 250, 300 300, 300 200,
100 200, 100 400))

Hole self touches to form two separate hole areas:

POLYGON ((100 400, 300 400, 300 200, 100 200, 100 400), (150 350, 250 350,
200 300, 250 250, 150 250, 200 300, 150 350))

and this is not:

Bow-tie - shell split into two areas by a self-touch

POLYGON ((100 400, 300 400, 200 300, 300 200, 100 200, 200 300, 100 400))


On Thu, Jan 14, 2016 at 4:00 PM, John Cartwright - NOAA Federal <

Post by John Cartwright - NOAA Federal
Hello All,
I'm confused about the isValidOp.setSelfTouchingRingFormingHoleValid(true)
method. Given a bow-tie polygon like the one below, I would have expected
setting the above option to cause the polygon to report as valid but it
doesn't.
​
Can someone please clarify for me?
Thanks!
--john
​//​
​//JTS version 1.14.0 with Groovy 2.4.5.​
//
wkt = '''POLYGON((1 1, 2 1, 1 2, 2 2, 1 1))'''
def geom = wktReader.read(wkt)
def validOp = new IsValidOp(geom)
validOp.setSelfTouchingRingFormingHoleValid(true)
//fails
assert geom.valid
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