Add an example using custom distance for nearest search

[aprokop]

Add an example that does nearest search using custom points and metric.

Drive-by change: remove couple unnecessary headers

[dalg24]

I would drop the callback to reduce complexity and explore defining struct MyPoint { float x, y; };

[dalg24]

Why did you elect to get distances out instead of indices?
I suspect indices would make it more obvious that the distance metric was changed.
I find the use of both a custom geometry with specialized distance computation mixed with a callback that recomputes the distance potentially confusing.

[aprokop]

I chose distances so that a user can see that the computed distances are indeed the custom ones. Computing just the found indices seems insufficient to me, as it still does not confirm that we can get the correct distance in the callback.

[aprokop]

explore defining struct MyPoint { float x, y; };

The whole point is for a user to not define their own type. The only thing that's necessary is to have a separate type for disambiguation during the dispatch.

[aprokop]

@dalg24 Do you have any blocking objections to merging the example in the current form?

[dalg24]

Formally blocking. I find the complexity unnecessary (along the lines of my previous comments)

[aprokop]

I chose distances so that a user can see that the computed distances are indeed the custom ones. Computing just the found indices seems insufficient to me, as it still does not confirm that we can get the correct distance in the callback.

@dalg24 If you find complexity unnecessary, please provide a reply to this comment.

[dalg24]

Please fix the header includes before you merge

[dalg24]

How comes we don't default that implementation?
(not blocking but we should consider fixing)

[aprokop]

We do. I removed it. It was from the time when CustomPoint did not have operator[], and returnCentroid returned ArborX::Point and not CustomPoint.