Accuracy of libkdtree

[Paul Harris]

Hi Walter,

So is the calculated Distance the inaccurate bit ?
Or is it that the points found were not the closest ?

Or is it the fact that it returned a result that was > 10.0f ?

thanks,
Paul

2009/1/15 Walter Keiner <walter.keiner at googlemail.com>

> Hello,
>
> I used libkdtree (ver 0.7.0) with floating point values and the function
> find_within_range() to get all values within a specified range.
> Unfortunately, the accuracy of the results have been poor. I used two set of
> points. The first one:
>
> x=18.892500 y=20.341400 z=-1.188940
> x=18.446899 y=18.649700 z=-2.155560
> x=18.228800 y=16.921600 z=-2.665970
>
> And the second one:
>
> x=28.771200 y=16.921600 z=-2.665970
> x=28.553101 y=18.649700 z=-2.155560
> x=28.107500 y=20.341400 z=-1.188940
>
> If you insert the second set into the kdtree and check all points of the
> first one with find_within_range(sv, 10.0f, std::back_inserter(vectors));
> you get the following result:
>
> info: distance = 10.557716 with :
>
> info: x=18.892500 y=20.341400 z=-1.188940
>
> Info: x=28.771200 y=16.921600 z=-2.665970
>
>
> Info: distance = 9.855121 with :
>
> Info: x=18.892500 y=20.341400 z=-1.188940
>
> Info: x=28.553101 y=18.649700 z=-2.155560
>
>
> Info: distance = 9.215000 with :
>
> Info: x=18.892500 y=20.341400 z=-1.188940
>
> Info: x=28.107500 y=20.341400 z=-1.188940
>
>
> Info: distance = 9.855121 with :
>
> Info: x=18.446899 y=18.649700 z=-2.155560
>
> Info: x=28.107500 y=20.341400 z=-1.188940
>
> The distance is calculated by the norm of the difference vector between the
> two provided. As you can see the there is a value with a distance >10, also
> find_within_range was provided with 10.0f.
>
> The Tree was defined:
>
> struct sVECTOR
> {
>         float v[3];
>         //some other values
>  };
>
>  typedef KDTree::KDTree<3, sVECTOR,
> std::pointer_to_binary_function<sVECTOR, size_t, float> > tTreeType;
>
> The tree was allocated with:
>
> tree = new tTreeType(std::ptr_fun(tac));
>
> where tac is:
>
> inline float KDTreeHandler::tac( KDTreeHandler::sVECTOR t, size_t k )
> {
>     return t.v[k];
> }
>
> The variable vectors provided for find_within_range is a
> std::deque<sVECTOR>.
>
> Can anyone give me some advices or recommendations?
>
> Grettings,
> Walter
>
>
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>
>
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