| Clustering x,y coordinates with IDL? [message #70220] |
Mon, 29 March 2010 02:44  |
Maxwell Peck
Messages: 61
Registered: February 2010
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Member |
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Hi All, This is not strictly an IDL question but I'm hoping it's
something simple to do and I'm not missing something painfully
obvious!
I have a set of x,y values e.g.
x = [34.5,36.7,35.6,80.5,81.2,79.3]
y = [50.6,51.2,53.2,48.5,50.3,51.2]
The values will be sparsely clustered overall but tightly within an
approximate 10x10 box. What I'd like to do is replace each clusters
values with the average x,y value. This doesn't have to be 'perfect',
the edges aren't that important.
My initial thought was to use hist_2d or hist_nd to try and calculate
the 2d histogram with a binsize of 10 and use this to average the
values but I can't get it to work. My other thought was using griddata
or something similar, or at worst generating an approximate binary
image and running a window over it.
Any advice or suggestions would be appreciated.
Regards
Max
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| Re: Clustering x,y coordinates with IDL? [message #70311 is a reply to message #70220] |
Mon, 29 March 2010 13:20  |
Maxwell Peck
Messages: 61
Registered: February 2010
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Member |
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On Mar 30, 2:38 am, Mort Canty <m.ca...@fz-juelich.de> wrote:
> Am 29.03.2010 11:44, schrieb Maxwell Peck:
>
>
>
>> Hi All, This is not strictly an IDL question but I'm hoping it's
>> something simple to do and I'm not missing something painfully
>> obvious!
>
>> I have a set of x,y values e.g.
>
>> x = [34.5,36.7,35.6,80.5,81.2,79.3]
>> y = [50.6,51.2,53.2,48.5,50.3,51.2]
>
>> The values will be sparsely clustered overall but tightly within an
>> approximate 10x10 box. What I'd like to do is replace each clusters
>> values with the average x,y value. This doesn't have to be 'perfect',
>> the edges aren't that important.
>
>> My initial thought was to use hist_2d or hist_nd to try and calculate
>> the 2d histogram with a binsize of 10 and use this to average the
>> values but I can't get it to work. My other thought was using griddata
>> or something similar, or at worst generating an approximate binary
>> image and running a window over it.
>
>> Any advice or suggestions would be appreciated.
>
>> Regards
>
>> Max
>
> The IDL function CLUSTER() implements k-means clustering. I think that's
> what you want.
>
> Mort
Thanks Mort. I had seen this I am concerned though about how it will
deal with single/a few points as opposed to real 'clusters'. Also the
distance with which points are considered to be a cluster as well is
concerning. I will give it a bash anyway and see how it looks. I had
thought there must be a nice way to do it with histogram but I just
can't get it to work.
Regards
Nax
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| Re: Clustering x,y coordinates with IDL? [message #70315 is a reply to message #70220] |
Mon, 29 March 2010 08:38 |
Mort Canty
Messages: 134
Registered: March 2003
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Senior Member |
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Am 29.03.2010 11:44, schrieb Maxwell Peck:
> Hi All, This is not strictly an IDL question but I'm hoping it's
> something simple to do and I'm not missing something painfully
> obvious!
>
> I have a set of x,y values e.g.
>
> x = [34.5,36.7,35.6,80.5,81.2,79.3]
> y = [50.6,51.2,53.2,48.5,50.3,51.2]
>
> The values will be sparsely clustered overall but tightly within an
> approximate 10x10 box. What I'd like to do is replace each clusters
> values with the average x,y value. This doesn't have to be 'perfect',
> the edges aren't that important.
>
> My initial thought was to use hist_2d or hist_nd to try and calculate
> the 2d histogram with a binsize of 10 and use this to average the
> values but I can't get it to work. My other thought was using griddata
> or something similar, or at worst generating an approximate binary
> image and running a window over it.
>
> Any advice or suggestions would be appreciated.
>
> Regards
>
> Max
>
The IDL function CLUSTER() implements k-means clustering. I think that's
what you want.
Mort
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