dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Sat, Feb 20, 2010 at 01:06:17AM -0000, Andre Massing wrote:
> Question #101686 on DOLFIN changed:
> https://answers.launchpad.net/dolfin/+question/101686
>
> Andre Massing proposed the following answer:
>
> Garth N. Wells wrote:
> >
> > Andre Massing wrote:
> >> Question #101686 on DOLFIN changed:
> >> https://answers.launchpad.net/dolfin/+question/101686
> >>
> >>     Status: Open => Answered
> >>
> >> Andre Massing proposed the following answer:
> >> On Friday 19. February 2010 18.33.47 marc spiegelman wrote:
> >>  > New question #101686 on DOLFIN:
> >>  > https://answers.launchpad.net/dolfin/+question/101686
> >>  >
> >>  > Hi All,
> >>  >    I've implemented a rather nifty semi-lagrangian advection scheme in
> >>  >  dolfin that requires rapid checking to see if a point intersects a
> >>  >  cell
> >>  >  (without necessarily firing up the full intersection operator).  Pre
> >>  >  0.9.7
> >>  >  this was implemented as cell.intersects(point).
> >>  >
> >>  > Everything works fine in 0.9.6   with the new CGAL intersection
> >>  > operator
> >>  > replacing the GTS intersection operator (with about a 20% speedup).
> >>
> >> Did you only use the intersection between meshentities and points or did
> >> you
> >> use also the new mesh intersection operator? Just curious, because the
> >> former
> >> code for intersection between points og e.g. triangles did not change.
> >>
> >>  >  However, in 0.9.7 the code breaks because  cell.intersects() has been
> >>  >  removed as a GTS dependency (actually, looking at
> >>  >  TriangleCell.intersects(point), it looks like it simply reproduces
> >>  >  GTS
> >>  >  code but wasn't actually dependent on GTS)
> >>
> >> Yep that's true, the intersection functions was removed and there is a new
> >> PrimitiveIntersector class in C++ with two static functions. These computes
> >> the intersection between rather arbitrary mesh entities (exact or only
> >> using
> >> doubling precision). The functions are exposed as do_intersect and
> >> do_intersect_exact in the python interface. But you are right, a point -
> >> meshentity intersection is not provided. I attached a patch against the
> >> recent
> >> 0.9.7 release. Could you can apply to you sources and see whether it
> >> works for
> >> you?
> >>
> >
> > Andre: Did you forget to attach it?
>
> Hmm, I did not, at least in my sent box it also appeared with
> attachment. Strange... resend it (CC to the DOLFIN-ml).

We also need to add back the simple interface

  bool MeshEntity::intersects(const Foo& foo) const;

where foo can be either a Point or another MeshEntity.

do_intersect looks a bit strange to me. (But it might be good for the
low-level interface that interacts with the CGAL templates.)

--
Anders

Attachment: signature.asc
Description: Digital signature