Re: Repeats and Triangulation

[Ben Tupper <pemaquidriver(at)tidewater.net>]

Thanks Craig,

I think I'll pursue you final suggestion.  The tricky part there is that it is
possible to have indices repeated not only within column 1 but also apprearing
in column 2.

Ben

Craig Markwardt wrote:

> Ben Tupper <pemaquidriver@tidewater.net> writes:
> > The REPEATS keyword to TRIANGULATION returns a 2,n element
> > array of pairs indices of repeated values.  If no values are
> > repeated then REPEATS = [-1,-1].  My question is 'How do I
> > pull out the repeated values efficiently?'
> >
> ...
> >  ;make the polygon descriptor (see IDLgrPolyLine)
> > List = Conn[Conn[0]:Conn[1]-1L]
> > Ptr = Ptr_NEW([N_elements(List),List])
> > For  i = 1, n_elements(X) -1 DO Begin
> >  List = Conn[conn[i]:Conn[i+1]-1]
> >  *Ptr = [*Ptr, n_elements(List), List]
> > EndFor
>
> Umm, while the procedure does not document how it treats repeated
> points -- which might be considered a documentation bug -- the format
> of the adjacency list is very similar to the output from the
> REVERSE_INDICES keyword of HISTOGRAM.  That is, there are bins that
> have no entries, and there is a way to ignore them.  How about
> inserting an IF clause which tests for this?
>
> List = Conn[Conn[0]:Conn[1]-1L]
> Ptr = Ptr_NEW([N_elements(List),List])
> For  i = 1, n_elements(X) -1 DO IF CONN[i+1] GT CONN[i] then Begin
>  List = Conn[conn[i]:Conn[i+1]-1]
>  *Ptr = [*Ptr, n_elements(List), List]
> EndIf
>
> The above solution works for me.
>
> Your other options are to:
>  * pre-check your point list to remove repeats.  This might be done
>    similar to UNIQ.
>  * use the REPEATS array to remove duplicates.
>    DELMASK = lonarr(n_elements(x))
>    DELMASK (REP(1,*)) = 1
>    and then check DELMASK(i) EQ 1 before adding the point to your list.
>
> Good luck,
> Craig
>
> --
> --------------------------------------------------------------------------
> Craig B. Markwardt, Ph.D.         EMAIL:    craigmnet@cow.physics.wisc.edu
> Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
> --------------------------------------------------------------------------

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Ben Tupper
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