# Re: How to find closest point(s) around a specific point in point cloud?

On Mar 31, 5:33 pm, Willem <wil...@xxxxxxxx> wrote:
Ed wrote:

) Why hard? We are working in integer dimensions.
) Given point 5,4,3 the unit shell (points exactly 1 unit away)
) includes the points
) 5,4,4
) 5,4,2
) 6,4,3
) 4,4,3
) 5,5,3
) 5,3,3

The OP was talking about a list with a couple hundred of points.
You're talking about *all* points with integer coordinates.

To solve the OP's problem you still need to search through the given
list of points to find the ones that match the box you just described.

) The key of what I am suggesting is not to start the search at 0,0,0.
) Maybe I assumed wrong that your suggestion of linear search starts
) there and not at the point of interest.

The 'linear search' has nothing to do with starting at 0,0,0 or anywhere
else. It means that you have to look at each point in the list to see if
it may be one of the 10 closest points.

)> Even if the shell were rectilinear it would be more than just 'tricky'.
)> How are you going to find all points that fall inside a given box without
)> looking at most (if not all) of the points ?
)
) the coordinates are integers. it is an array space, not a real
) coordinate space. That simplifies the search.

I think you misunderstood the OP's question.

He has a list of points. Not a 3D array where each item is a location.

For your suggestion to work he would have to create a full-blown 3-D array
where each entry specifies which, if any, points there are at that location.

SaSW, Willem
--
Disclaimer: I am in no way responsible for any of the statements
made in the above text. For all I know I might be
drugged or something..
No I'm not paranoid. You all think I'm paranoid, don't you !
#EOT

His original post said "I have an array". So why you think it is a
list, I do not understand.

If it is a list, then your comments are spot on, except I do not quite
understand you last sentence above. His problem statement was each
position has a value. He wanted to find a list of points closest to a
given point where the value at those points met some condition (e.g
40). At least that is how I read his post.

Some of us are confused on the requirements which is leading to these
apparent disagreements (because we are solving different problems!).
Ed
.

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