CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

On 09/04/2012 05:32 PM, mathog wrote:
> Given a 2D path P consisting of a series of linear and bezier
> segments, and a path distance pair {start,end} measured from a point
> in P, can CGAL return the subpath corresponding to the section of P
> inclusive of the distances from start to end?
>
> If so how?
>
> This is for an application that needs to convert a path with an
> arbitrary dot/dash pattern into a set of discrete paths, because a 2nd
> application which needs to read this data has no other support for
> reading dotted/dashed pairs. In the first application the pattern is
> actually written as a series of emit/omit lengths, for example
> {3,1,2,1}, which would emit 0->3, omit 3->4, emit 4->6, omit 6->7,
> then repeat lengths again. Implementing this loop would be fastest if
> CGAL had something like (pseudocode)
>
> new subpath = get_subpath(P, &point_on_P, start, end, &wrap);
>
> where point_on_P would initially be the first point in P and the
> method/function returned the point corresponding to "end". Wrap would
> return a value >0 whenever the subpath start->end fell on or beyond
> P.end() (not the start point), and would be the length beyond which
> the specified interval extended. So for the 3,1,2,1 example the calls
> would be (not including tests on wrap)
>
> point_on_P = P.begin();
> path1 = get_subpath(P, &point_on_p, 0, 3, &wrap); // 3 dash
> path2 = get_subpath(P, &point_on_p, 1, 3, &wrap); // 2 dash
> path3 = get_subpath(P, &point_on_p, 1, 4, &wrap); // 3 dash
> path4 = get_subpath(P, &point_on_p, 1, 3, &wrap); // etc.
> path5 = get_subpath(P, &point_on_p, 1, 4, &wrap);
>
> Thank you.
>
> David Mathog
>
> Manager, Sequence Analysis Facility, Biology Division, Caltech
I probably did not get what you want because to me it looks like you
need to extract subsets of points from a container and put that into
another container. In that case, using STL algorithms is sufficient.



Sebastien.