[GEOS] #974: Union of Polylines results in additional segments

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[GEOS] #974: Union of Polylines results in additional segments

geos-2
#974: Union of Polylines results in additional segments
------------------------+------------------------------
 Reporter:  jerryfaust  |      Owner:  geos-devel@…
     Type:  defect      |     Status:  new
 Priority:  minor       |  Milestone:
Component:  Default     |    Version:  3.4.2
 Severity:  Unassigned  |   Keywords:  UNION UNARYUNION
------------------------+------------------------------
 Hello.

 Hopefully I'm overlooking something simple.  I am selecting a group of
 roads.  I want to Union and Buffer them in order to search within the
 resulting polygon.

 However, when I get back the union, there are additional line segments
 that did not exist in the original set.

 I've tried individually Union'ing them, I've tried UnaryUnion of a multi-
 part polyline (MultiLineString). I've also clipper calls.  And I always
 get a similar result.

 I've tried reording the lines as I union them [[Image()]]so that each
 union operation always involves line segments that touch eachother.

 I'm hoping that there is something that I'm simply overlooking, or not
 understanding, or not using properly.

 I'm attaching a snapshot of the circle used to 'select' the streets.  I'm
 expecting a result something like a '#' sign, or tic-tac-toe.  But I get
 additional diagonal lines in the result set.

 Thank you for any feedback.

 Regards.
 Jerry.

--
Ticket URL: <https://trac.osgeo.org/geos/ticket/974>
GEOS <http://trac.osgeo.org/geos>
GEOS (Geometry Engine - Open Source) is a C++ port of the Java Topology Suite (JTS).

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Re: [GEOS] #974: Union of Polylines results in additional segments

geos-2
#974: Union of Polylines results in additional segments
------------------------------+---------------------------
 Reporter:  jerryfaust        |       Owner:  geos-devel@…
     Type:  defect            |      Status:  new
 Priority:  minor             |   Milestone:
Component:  Default           |     Version:  3.4.2
 Severity:  Unassigned        |  Resolution:
 Keywords:  UNION UNARYUNION  |
------------------------------+---------------------------
Changes (by jerryfaust):

 * Attachment "Circular Container.PNG" added.


--
Ticket URL: <https://trac.osgeo.org/geos/ticket/974>
GEOS <http://trac.osgeo.org/geos>
GEOS (Geometry Engine - Open Source) is a C++ port of the Java Topology Suite (JTS).

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Re: [GEOS] #974: Union of Polylines results in additional segments

geos-2
In reply to this post by geos-2
#974: Union of Polylines results in additional segments
------------------------------+---------------------------
 Reporter:  jerryfaust        |       Owner:  geos-devel@…
     Type:  defect            |      Status:  new
 Priority:  minor             |   Milestone:
Component:  Default           |     Version:  3.4.2
 Severity:  Unassigned        |  Resolution:
 Keywords:  UNION UNARYUNION  |
------------------------------+---------------------------
Changes (by jerryfaust):

 * Attachment "Unioned Streets.PNG" added.


--
Ticket URL: <https://trac.osgeo.org/geos/ticket/974>
GEOS <http://trac.osgeo.org/geos>
GEOS (Geometry Engine - Open Source) is a C++ port of the Java Topology Suite (JTS).

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Re: [GEOS] #974: Union of Polylines results in additional segments

geos-2
In reply to this post by geos-2
#974: Union of Polylines results in additional segments
------------------------------+---------------------------
 Reporter:  jerryfaust        |       Owner:  geos-devel@…
     Type:  defect            |      Status:  new
 Priority:  minor             |   Milestone:
Component:  Default           |     Version:  3.4.2
 Severity:  Unassigned        |  Resolution:
 Keywords:  UNION UNARYUNION  |
------------------------------+---------------------------

Comment (by komzpa):

 Hi,

 Can you share a snippet of code how you do it?
 (Coming from PostGIS land this looks like ST_MakeLine GEOS analogue used
 instead of ST_Union)

 I haven't seen this behavior accessing GEOS via PostGIS.

--
Ticket URL: <https://trac.osgeo.org/geos/ticket/974#comment:1>
GEOS <http://trac.osgeo.org/geos>
GEOS (Geometry Engine - Open Source) is a C++ port of the Java Topology Suite (JTS).

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Re: [GEOS] #974: Union of Polylines results in additional segments

geos-2
In reply to this post by geos-2
#974: Union of Polylines results in additional segments
------------------------------+---------------------------
 Reporter:  jerryfaust        |       Owner:  geos-devel@…
     Type:  defect            |      Status:  new
 Priority:  minor             |   Milestone:
Component:  Default           |     Version:  3.4.2
 Severity:  Unassigned        |  Resolution:
 Keywords:  UNION UNARYUNION  |
------------------------------+---------------------------

Comment (by mdavis):

 this seems like a straightforward case for unioning lines, so it's very
 unlikely the problem is in GEOS.  It's more likely to be caused by how
 GEOS is called.  This has the appearance of a situation where the client
 code is providing the lines as a single list of coordinates, rather than a
 set of individual linestrings.

 If possible please post a code snippet or even better a self-contained
 unit test showing the behaviour.

--
Ticket URL: <https://trac.osgeo.org/geos/ticket/974#comment:2>
GEOS <http://trac.osgeo.org/geos>
GEOS (Geometry Engine - Open Source) is a C++ port of the Java Topology Suite (JTS).

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Re: [GEOS] #974: Union of Polylines results in additional segments

geos-2
In reply to this post by geos-2
#974: Union of Polylines results in additional segments
------------------------------+---------------------------
 Reporter:  jerryfaust        |       Owner:  geos-devel@…
     Type:  defect            |      Status:  new
 Priority:  minor             |   Milestone:
Component:  Default           |     Version:  3.4.2
 Severity:  Unassigned        |  Resolution:
 Keywords:  UNION UNARYUNION  |
------------------------------+---------------------------

Comment (by jerryfaust):

 Thank you for the feedback.

 I walked through the process again and found MY error.  During one of the
 steps in my process, while reprojecting the points of the multi-part line,
 I lost the 'Parts', so it became an oddly connected single linestring.

 Thanks again.

--
Ticket URL: <https://trac.osgeo.org/geos/ticket/974#comment:3>
GEOS <http://trac.osgeo.org/geos>
GEOS (Geometry Engine - Open Source) is a C++ port of the Java Topology Suite (JTS).

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Re: [GEOS] #974: Union of Polylines results in additional segments

geos-2
In reply to this post by geos-2
#974: Union of Polylines results in additional segments
------------------------------+---------------------------
 Reporter:  jerryfaust        |       Owner:  geos-devel@…
     Type:  defect            |      Status:  closed
 Priority:  minor             |   Milestone:
Component:  Default           |     Version:  3.4.2
 Severity:  Unassigned        |  Resolution:  invalid
 Keywords:  UNION UNARYUNION  |
------------------------------+---------------------------
Changes (by komzpa):

 * status:  new => closed
 * resolution:   => invalid


Comment:

 Thanks for the update. Have a good day.

--
Ticket URL: <https://trac.osgeo.org/geos/ticket/974#comment:4>
GEOS <http://trac.osgeo.org/geos>
GEOS (Geometry Engine - Open Source) is a C++ port of the Java Topology Suite (JTS).

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