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[Andre Massing <question101686@xxxxxxxxxxxxxxxxxxxxx>]

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).

> 
>>  >
>>  > The question is... is there is any equivalent functionality in CGAL 
>> and is
>>  > anyone interested in implementing it (either as cell.intersects(??)
>>  > or some other interface).  The functionality should be straightforward
>>  > (and I'd be surprised if it didn't exist), given a *known cell* and a
>>  >  point, does the cell intersect the point.  This would be useful for
>>  >  particle based methods as well.
>>  >
>>  > On a related note...are there any plans for a parallel implementation 
>>  > of Function::eval(Array<double>& values, const Array<double>& x) by
>>  > release 1.0?
> 
> I've just pushed a change for this, although it won't work for
> off-process points.
> 
> Garth
> 
>>  >
>>  > All assistance greatly appreciated
>>
>> Any feedback as well :)
>>
>>  > marc
>>  >
>>
> 
> 
> 
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