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<p class=MsoNormal><font size=2 face=Arial><span lang=EN-CA style='font-size:
10.0pt;font-family:Arial'>I’m asking for advice here: What is the
most robust (numerically stable) way to use GEOS? What are its
limitations?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-CA style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-CA style='font-size:
10.0pt;font-family:Arial'>For our purposes we need to use code that is both as
fast and accurate as possible. As you probably know, when using a complex
algorithm sometimes even small inaccuracies in geometric computations can
compound into drastically incorrect results.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-CA style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-CA style='font-size:
10.0pt;font-family:Arial'>Here is a concrete example from real customer data:<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-CA style='font-size:
10.0pt;font-family:Arial'>I have created two simple 2-point LINEs and used the
GEOS call to get the spot where they intersect:<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-CA style='font-size:
10.0pt;font-family:Arial'>point = lineA.intersection(lineB);<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-CA style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-CA style='font-size:
10.0pt;font-family:Arial'>lineA = from (2089426.5233462777,1180182.3877339689)
to (2085646.6891757075,1195618.7333999649)<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-CA style='font-size:
10.0pt;font-family:Arial'>lineB = from (1889281.8148903656,1997547.0560044837)
to (2259977.3672235999,483675.17050843034)<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-CA style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-CA style='font-size:
10.0pt;font-family:Arial'>the intersection point I get back is this:<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-CA style='font-size:
10.0pt;font-family:Arial'>point = (2097408.2633752143,1144595.8008114607)<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-CA style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-CA style='font-size:
10.0pt;font-family:Arial'>This point is a significant distance away from any
part of lineA. If one were to place this intersection point between the
start and end points of lineA, the resulting line would look ridiculous.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-CA style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-CA style='font-size:
10.0pt;font-family:Arial'>JTS returns the same result.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-CA style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-CA style='font-size:
10.0pt;font-family:Arial'>Depending on your explanations for this I may have
some technical advice.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-CA style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-CA style='font-size:
10.0pt;font-family:Arial'>Thanks for your comments,<o:p></o:p></span></font></p>
<p class=MsoNormal style='text-autospace:none'><font size=2 face=Arial><span
style='font-size:10.0pt;font-family:Arial'>-Kevin-<o:p></o:p></span></font></p>
<p class=MsoNormal style='text-autospace:none'><font size=2 face=Arial><span
style='font-size:10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='text-autospace:none'><font size=2 face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New"'>----------------------------------------------------------------<o:p></o:p></span></font></p>
<p class=MsoNormal style='text-autospace:none'><font size=2 face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New"'> Kevin
Wiebe Safe Software
Inc.
kevin@safe.com<o:p></o:p></span></font></p>
<p class=MsoNormal style='text-autospace:none'><font size=2 face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New"'>
Senior Surrey, BC,
CANADA phone: (604) 501-9985<o:p></o:p></span></font></p>
<p class=MsoNormal style='text-autospace:none'><font size=2 face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New"'>
Developer
http://www.safe.com fax: (604)
501-9965<o:p></o:p></span></font></p>
<p class=MsoNormal style='text-autospace:none'><font size=2 face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New"'>----------------------------------------------------------------<o:p></o:p></span></font></p>
<p class=MsoNormal style='text-autospace:none'><font size=2 face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New"'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='text-autospace:none'><font size=2 face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New"'> <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-CA style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
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