#1000: behavior of GEOSCoordSeq_isCCW() is unclear when input is not a simple
closed curve
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Reporter: sirsigurd | Owner: geos-devel@…
Type: defect | Status: new
Priority: major | Milestone:
Component: Default | Version: 3.7.0
Severity: Unassigned | Keywords:
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Here's GEOSCoordSeq_isCCW() doc from C API header:
{{{
/*
* Check orientation of a CoordinateSequence and set 'is_ccw' to 1
* if it has counter-clockwise orientation, 0 otherwise.
* Return 0 on exception, 1 on success.
*/
extern int GEOS_DLL GEOSCoordSeq_isCCW_r(GEOSContextHandle_t handle,
const GEOSCoordSequence* s,
char* is_ccw);
}}}
As I understand from [https://en.wikipedia.org/wiki/Curve_orientation
Wikipedia], 'orientation' is defined only for simple closed curves
(hereafter referred to as SCC).
So from my perspective GEOSCoordSeq_isCCW() could follow one these
approaches for input which is not SCC:
1. Orientation is defined only for SCC, so if input is not SCC, it can't
be CCW-oriented curve (is_ccw = 0).
2. Orientation is defined only for SCC, so if input is not SCC, it's
invalid (error code is returned)
Currently GEOSCoordSeq_isCCW() doesn't follow any of these approaches
consistently. If coordinate sequence has less than 4 points error code is
returned. At later stage if it turns out that there are less than 3
distinctive points is_ccw is set to 0.
--
Ticket URL: <https://trac.osgeo.org/geos/ticket/1000>
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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