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<p style="margin-top:0;margin-bottom:0">The intersectionpoint macro, based on the intersectiontimes
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<p style="margin-top:0;margin-bottom:0">primitive, works by succesively subdividing the two paths
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<p style="margin-top:0;margin-bottom:0">and determining whether the parts are close together. It stops
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<p style="margin-top:0;margin-bottom:0">when the range of the time parameter has been narrowed down
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<p style="margin-top:0;margin-bottom:0">to some preset tiny parameter. <br>
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<p style="margin-top:0;margin-bottom:0">It is mainly luck if this produces the mathematically exact
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<p style="margin-top:0;margin-bottom:0">intersection point. This seems to be especially true if the
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<p style="margin-top:0;margin-bottom:0">point of intersection is a node of both paths. In that
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<p style="margin-top:0;margin-bottom:0">case, the algorithm can even falsely conclude that there is
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<p style="margin-top:0;margin-bottom:0">no intersection. <br>
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<p style="margin-top:0;margin-bottom:0">Coming within a distance less than .008 is good enough for
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<p style="margin-top:0;margin-bottom:0">drawing purposes, but one should not rely on the
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<p style="margin-top:0;margin-bottom:0">intersectionpoint even lying exactly on the paths that supposedly
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<p style="margin-top:0;margin-bottom:0">intersect there.<br>
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<p style="margin-top:0;margin-bottom:0">Dan,<br>
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<div style="font-family:Tahoma; font-size:13px"><font size="3" face="Courier New">Daniel H. Luecking [luecking@uark.edu]
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Department of Mathematical Sciences<br>
1 University of Arkansas<br>
Fayetteville, AR, USA 72701-1201</font><br>
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<div id="divRplyFwdMsg" dir="ltr"><font style="font-size:11pt" face="Calibri, sans-serif" color="#000000"><b>From:</b> metapost <metapost-bounces+luecking=uark.edu@tug.org> on behalf of Walt Burkhard <burkhard@cs.ucsd.edu><br>
<b>Sent:</b> Tuesday, October 2, 2018 12:37 PM<br>
<b>To:</b> Metapost List<br>
<b>Subject:</b> [metapost] another question</font>
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Hello,</div>
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I have another question for the program attached below. The program is to round out the corner of two intersecting paths. </div>
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When it runs, the intersectionpoint does not seem to work correctly. The program makes three calls to intersectionpoint, the first two seem to work as expected. The third is to return the pair (120 ,300) but </div>
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instead returns something close (119.99693. 299.99229). </div>
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Using numbersystem = double does not resolve this issue. What is going on here?</div>
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Any suggestions would be appreciated. Many thanks in advance. </div>
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Walt Burkhard </div>
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