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From Curtis Jensen <cur...@the-jensens.org>
Subject Re: SubLine Intersection Math 3.0
Date Tue, 14 Jun 2011 23:27:16 GMT
Got it working (added some Jira issues too).  Thanks.

--
Curtis


On Tue, Jun 14, 2011 at 11:53 AM, Luc Maisonobe <Luc.Maisonobe@free.fr> wrote:
> Hi Curtis,
>
> Le 14/06/2011 19:38, Curtis Jensen a écrit :
>>
>> In the commons math 3.0 Geometry package, How can get the intersection
>> of two SubLines?  I see that the Line class has an intersection
>> method, but not the SubLine class.  I can create Lines from SubLines
>> and call the intersection method, but I'm not sure how to tell if the
>> resultant Vector is on the SubLines.
>
> There is not (yet) any convenient method to get such a point. However, it
> would be interesting to add one. Feel free to open a Jira issue to ask for
> it ig you want.
>
> In the mean time, the proper way to compute this point is as follows:
>
>  // retrieve the underlying lines (it does not recreate them)
>  Line line1 = (Line) subLine1.getHyperplane();
>  Line line2 = (Line) subLine2.getHyperplane();
>
>  // compute the intersection on infinite line
>  Vector2D v2D = line1.intersection(line2);
>
>  // check location of point with respect to first sub-line
>  Location loc1 =
>    sub1.getRemainingRegion().checkPoint(l1.toSubSpace(v2D));
>
>  // check location of point with respect to second sub-line
>  Location loc2 =
>    sub2.getRemainingRegion().checkPoint(l2.toSubSpace(v2D));
>
> You can the compare loc1 and loc2 as you want. If you want strict inclusion
> (i.e. without endpoints) you should simply do
>
>  if ((loc1 == INSIDE) && (loc2 == INSIDE)) {
>     return v2D;
>  } else {
>     return null; // or throw an exception
>  }
>
> and if you want to large inclusion (i.e. with endpoints) you should do
>
>  if ((loc1 != OUTSIDE) && (loc2 != OUTSIDE)) {
>     return v2D;
>  } else {
>     return null; // or throw an exception
>  }
>
> There are three possible values for Location: INSIDE, OUTSIDE and BOUNDARY.
>
>>
>> Also, How do I get the end points of the SubLine.
>
> Here again, there is no convenience function. If you are sure you subline is
> only one segment and not several disjoints segments, you can do:
>
>  IntervalSet is = (IntervalsSet) sub1.getRemainingRegion();
>  Vector2D start = line1.toSpace(new Vector1D(is.getInf()));
>  Vector2D end   = line1.toSpace(new Vector1D(is.getSup()));
>
> If there may be several disjoint segments, use the asList method from
> IntervalSet to retrieve all segments, and perform a loop to convert the 1D
> abscissa into a 2D point, using line.toSpace.
>
> Here again, if you think it would be interesting, open a Jira issue to ask
> for a convenience function for that. In the same spirit, I guess a
> constructor with the two endpoints may be interesting.
>
> Hope this helps
> Luc
>
>>
>> Thanks,
>> Curtis
>>
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>
>
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