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Re: fast search [message #50811 is a reply to message #50803]

Tue, 17 October 2006 07:15

greg michael
Messages: 163
Registered: January 2006

Senior Member

Hi Marie,

Also take a look at this thread...

http://groups.google.de/group/comp.lang.idl-pvwave/browse_th read/thread/1d020842b165598a/8e57c4b2c3841851?#8e57c4b2c3841 851

A program to search for pairs closer than a given distance d in a point
cloud. It recursively cuts up the volume until there are fewer than a
given threshold of points in the subvolume, and then directly compares
those few. At each cutting of the space, it's necessary to leave an
overlap of d so that points in adjoining subvolumes aren't missed. I
don't remember - looks like it might be necessary to check for the
uniqueness of the solutions at the end. Anyway, the recursion is the
fun part...

By the way, it looks like there are a lot of for-loops there, but
they're powerful ones - each run of the loop cuts the space.

regards,
Greg

m.goullant@gmail.com wrote:
> Hi there,
>
> I have the following problem:
>
> ;data structure of an irregular point cloud
> x = points.x
> y = points.y
> z = points.z
>
> search radio
> radio = 8
>
> FOR i=0L,N_ELEMENTS(z)-1 DO BEGIN
>
> square = WHERE(x LE x[i] + radio AND x GE x[i] - radio AND y LE
> y[i] + radio AND y GE y[i] - radio)
> ;(...)
>
> ENDFOR
>
> I realize that WHERE will do the job, but at very low efficiency.
> WHERE
> makes no assumptions about the list being ordered. It seems to me it
> has
> to check every element of the array, requiring N steps for an N-element
> array
>
> There is a faster way to do this?
>
> thanks,
> Marie

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[Message index]

		Re: fast search By: greg michael on Wed, 18 October 2006 08:25
		Re: fast search By: greg michael on Tue, 17 October 2006 11:25
		Re: fast search By: greg michael on Tue, 17 October 2006 10:17
		Re: fast search By: greg michael on Tue, 17 October 2006 07:15
		Re: fast search By: Paolo Grigis on Tue, 17 October 2006 05:53
		Re: fast search By: m.goullant@gmail.com on Thu, 19 October 2006 04:01
		Re: fast search By: m.goullant@gmail.com on Thu, 19 October 2006 03:46

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