Hi,
Unfortunately there's no rule or metric about which operations will
fail on invalid geometry. It all comes down to the details of the
algorithm. For instance, overlay ops are likely to fail, whereas
buffer is relatively robust (although with the caveat that for an
invalid geometry the result may not be what is "expected"). In some
cases this is noted in the Javadoc.
From my experience, TopologyException are also more likely to happen
while working with an integer PrecisionModel than with the double
precision model.
The bottom line is that geometry passed to any non-trivial JTS
operation should be known to be valid. There is a performance hit for
doing this, for sure. Perhaps an even bigger issue is: what do you do
with an invalid geometry? (Of course there are various heuristic ways
of cleaning it up, but in general this is context-dependent).
Generally it's best to ensure validity as early as possible in the
system, so that subsequent processing can proceed robustly. That's
why JTS leaves the question of when to do validity checking to the
client, since only they can know when it is appropriate and efficient
to do it.
A clear separation between validating and processing geometries is
probably a good thing. What is a bit frustrating for the user is that
JTS does not offer much tools to fix invalid geometries before
processing. I agree that there is not always one way to fix invalid
geometries, but even when the user knows what he wants, the work to do
it may be tedious. From my experience, the most frequent problems are :
- polygon with self-intersecting rings
most obvious solution : noding the rings and creating a MultiPolygon
doing it with JTS is difficult
- linestring with two identical points
most obvious solution : creating a Point
doing it with JTS is not difficult
- multipolygon with overlapping polygons
no obvious solution : merging ? making hole when possible ?
creating several features ?
- polygon with less than 4 points
most obvious solution : creating a LineString or even a Point
doing it with JTS is not difficult
...
Don't know what postgis ST_MakeValid does exactly, but a method to solve
the first case would be great in JTS.
My 2 cents,
Michaël
On Wed, May 21, 2014 at 8:00 AM, Rob Emanuele <[email protected]
<mailto:[email protected]>> wrote:
Thanks Martin. We were doing isValid checks other places in the
code (inside the wrapped geometry initializations), and I assumed
that was happening for MultiPolygon too, which it wasn't. And I
haven't quite internalized what vector data is invalid and what's
valid.
Is it the case that most operations will throw a TopologyException
for invalid geometries? I've been debating not putting the isValid
check inside the wrapped Geometry class initializers, since this
article:
http://www.vividsolutions.com/jts/caseStudy_largePolyValidation.htm worries
me about the potential performance hit of validating each geometry
on creation. But if most operations you would do with an invalid
polygon would throw TopologyExceptions, it might be worth it to
eat the performance hit and make sure everything is valid before
letting the user start working with the geometry, for the scala
wrapper.
On Tue, May 20, 2014 at 5:30 PM, Martin Davis <[email protected]
<mailto:[email protected]>> wrote:
The TopologyException occurs because the MultiPolygon is not
valid. The two components overlap (precisely, the first
polygon contains the second).
On Tue, May 20, 2014 at 2:17 PM, Rob Emanuele
<[email protected] <mailto:[email protected]>> wrote:
Hello,
I was wondering if I could get some insight on why this
would be throwing a TopologyException. I've been looking
through the JTS source, and trying different variations on
the MultiPolygon, but I can't seem to nail down what about
this is causing the issue (sorry for the scala code, I did
this example in the interpreter, but I think it should be
clear):
import com.vividsolutions.jts.geom._
val f = new GeometryFactory()
val l = f.createLineString(Array(new Coordinate(0,0), new
Coordinate(2,2)))
val exterior1 = f.createLinearRing(Array(new
Coordinate(0,0), new Coordinate(0,2), new Coordinate(2,2),
new Coordinate(2,0), new Coordinate(0,0)))
val exterior2 = f.createLinearRing(Array(new
Coordinate(0,0), new Coordinate(0,1), new Coordinate(2,1),
new Coordinate(2,0), new Coordinate(0,0)))
val p1 = f.createPolygon(exterior1, Array())
val p2 = f.createPolygon(exterior2, Array())
val mp = f.createMultiPolygon(Array(p1, p2))
mp.union(l)
Here is the exception thrown in the interpreter:
com.vividsolutions.jts.geom.TopologyException: side
location conflict [ (0.0, 1.0, NaN) ]
at
com.vividsolutions.jts.geomgraph.EdgeEndStar.propagateSideLabels(EdgeEndStar.java:300)
at
com.vividsolutions.jts.geomgraph.EdgeEndStar.computeLabelling(EdgeEndStar.java:136)
at
com.vividsolutions.jts.geomgraph.DirectedEdgeStar.computeLabelling(DirectedEdgeStar.java:127)
at
com.vividsolutions.jts.operation.overlay.OverlayOp.computeLabelling(OverlayOp.java:373)
at
com.vividsolutions.jts.operation.overlay.OverlayOp.computeOverlay(OverlayOp.java:173)
at
com.vividsolutions.jts.operation.overlay.OverlayOp.getResultGeometry(OverlayOp.java:127)
at
com.vividsolutions.jts.operation.overlay.OverlayOp.overlayOp(OverlayOp.java:66)
at
com.vividsolutions.jts.operation.overlay.snap.SnapIfNeededOverlayOp.getResultGeometry(SnapIfNeededOverlayOp.java:96)
at
com.vividsolutions.jts.operation.overlay.snap.SnapIfNeededOverlayOp.overlayOp(SnapIfNeededOverlayOp.java:58)
at
com.vividsolutions.jts.geom.Geometry.union(Geometry.java:1395)
at .<init>(<console>:18)
at .<clinit>(<console>)
at .<init>(<console>:7)
at .<clinit>(<console>)
at $print(<console>)
at
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at
scala.tools.nsc.interpreter.IMain$ReadEvalPrint.call(IMain.scala:734)
at
scala.tools.nsc.interpreter.IMain$Request.loadAndRun(IMain.scala:983)
at
scala.tools.nsc.interpreter.IMain.loadAndRunReq$1(IMain.scala:573)
at
scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:604)
at
scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:568)
at
scala.tools.nsc.interpreter.ILoop.reallyInterpret$1(ILoop.scala:756)
at
scala.tools.nsc.interpreter.ILoop.interpretStartingWith(ILoop.scala:801)
at
scala.tools.nsc.interpreter.ILoop.command(ILoop.scala:713)
at
scala.tools.nsc.interpreter.ILoop.processLine$1(ILoop.scala:577)
at
scala.tools.nsc.interpreter.ILoop.innerLoop$1(ILoop.scala:584)
at
scala.tools.nsc.interpreter.ILoop.loop(ILoop.scala:587)
at
scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply$mcZ$sp(ILoop.scala:878)
at
scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply(ILoop.scala:833)
at
scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply(ILoop.scala:833)
at
scala.tools.nsc.util.ScalaClassLoader$.savingContextLoader(ScalaClassLoader.scala:135)
at
scala.tools.nsc.interpreter.ILoop.process(ILoop.scala:833)
at
scala.tools.nsc.interpreter.ILoop.main(ILoop.scala:900)
at
xsbt.ConsoleInterface.run(ConsoleInterface.scala:57)
at
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at
sbt.compiler.AnalyzingCompiler.call(AnalyzingCompiler.scala:73)
at
sbt.compiler.AnalyzingCompiler.console(AnalyzingCompiler.scala:64)
at sbt.Console.console0$1(Console.scala:23)
at
sbt.Console$$anonfun$apply$2$$anonfun$apply$1.apply$mcV$sp(Console.scala:24)
at sbt.TrapExit$.executeMain$1(TrapExit.scala:33)
at sbt.TrapExit$$anon$1.run(TrapExit.scala:42)
Any insights on why this simple example is throwing?
Thanks,
Rob
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------------------------------------------------------------------------------
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Instantly run your Selenium tests across 300+ browser/OS combos.
Get unparalleled scalability from the best Selenium testing platform available
Simple to use. Nothing to install. Get started now for free."
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