cgal-discuss - problem with CGAL:intersection()

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problem with CGAL:intersection()

From: Michael Balzer <>
To:
Subject: problem with CGAL:intersection()
Date: Fri, 03 Aug 2007 17:37:42 +0200
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Hi,

I encountered a strange problem by making intersection tests between Line_2 and Segment_2. Sometimes, I get no intersections when there must be one.

Example (from debug output):
----------------------------
Debug: "edge from (1014,10) to (1014,718)"
Debug: "line.y_at_x( 1014 ) = 300.902"
Debug: "line.x_at_y( 10 ) = 1837.88"
Debug: "line.y_at_x( 1014 ) = 300.902"
Debug: "line.x_at_y( 718 ) = -167.281"
Debug: "CGAL::intersection( edge, line ): no intersection found"
Debug: "edge from (10,718) to (10,10)"
Debug: "line.y_at_x( 10 ) = 655.404"
Debug: "line.x_at_y( 718 ) = -167.281"
Debug: "line.y_at_x( 10 ) = 655.404"
Debug: "line.x_at_y( 10 ) = 1837.88"
Debug: "CGAL::intersection( edge, line ): intersection at (10,655.404)"

This means I have two vertical segments which both must have an intersection with the given line. But for the first segment I get no intersection. :(

My implementation is exactly the same as in the CGAL::intersection example in the manual. By the way, I'm using a CGAL::Cartesian< double> kernel.

Are their any known problems with this function, or has someone a hint what might be wrong?

Michael :)

problem with CGAL:intersection(), Michael Balzer, 08/03/2007

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problem with CGAL:intersection()