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Re: How 2 extract LOCAL Max? [message #68776]

Fri, 04 December 2009 11:12

jeffnettles4870
Messages: 111
Registered: October 2006

Senior Member

On Dec 4, 5:52 am, Dave_Poreh <d.po...@gmail.com> wrote:
> Folks
> I have a signal with few peaks (localmaximum). I need to extract the
> x and y of these Peaks programmatically. The input data is an array
> whit 2 column (x&y). What is the best way to do this?
> Any help highly appreciated
> Cheers
> Dave

Have a look at this thread:

http://groups.google.com/group/comp.lang.idl-pvwave/browse_f rm/thread/d70f405993359066/cc11ef2037032c6f?lnk=gst&q=lo cal+max#cc11ef2037032c6f

(or search for "Local max filter" in this newsgroup)

The stuff I found there worked very nicely for me as I recall.

Jeff

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Re: How 2 extract LOCAL Max? [message #68778 is a reply to message #68776]

Fri, 04 December 2009 04:12

greg.addr
Messages: 160
Registered: May 2007

Senior Member

> Dave_Poreh wrote:
>> Folks
>> I have a signal with few peaks (local maximum). I need to extract the
>> x and y of these Peaks programmatically. The input data is an array
>> whit 2 column (x&y). What is the best way to do this?
>
> "best" is a loaded word...
>
> /A/ way is to move along the array comparing values to their neighbours
> and see if things are going up/down, but you need to be quite careful
> about thresholds that will constitute a real peak (i.e., there can be
> plenty of false peak-lets caused by noise) and account for the fact that
> the signal might not really start to drop for several x increments.

You could apply a boxcar filter (e.g. median) with a width chosen to
exclude your interpretation of noise in the signal (or define your
notion of local), then search for points with adjacent lesser values
(possibly beyond adjacent equal values).

Greg

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Re: How 2 extract LOCAL Max? [message #68779 is a reply to message #68778]

Fri, 04 December 2009 03:59

Peter Clinch
Messages: 98
Registered: April 1996

Member

Dave_Poreh wrote:
> Folks
> I have a signal with few peaks (local maximum). I need to extract the
> x and y of these Peaks programmatically. The input data is an array
> whit 2 column (x&y). What is the best way to do this?

"best" is a loaded word...

/A/ way is to move along the array comparing values to their neighbours
and see if things are going up/down, but you need to be quite careful
about thresholds that will constitute a real peak (i.e., there can be
plenty of false peak-lets caused by noise) and account for the fact that
the signal might not really start to drop for several x increments.

If you find a peak then x will be whatever the count increment is and y
will be whatever the value is.

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net p.j.clinch@dundee.ac.uk http://www.dundee.ac.uk/~pjclinch/

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Re: How 2 extract LOCAL Max? [message #69017 is a reply to message #68776]

Wed, 09 December 2009 06:11

d.poreh
Messages: 406
Registered: October 2007

Senior Member

On 4 Dez., 11:12, "Jeff N." <jeffnettles4...@gmail.com> wrote:
> On Dec 4, 5:52 am, Dave_Poreh <d.po...@gmail.com> wrote:
>
>> Folks
>> I have a signal with few peaks (localmaximum). I need to extract the
>> x and y of these Peaks programmatically. The input data is an array
>> whit 2 column (x&y). What is the best way to do this?
>> Any help highly appreciated
>> Cheers
>> Dave
>
> Have a look at this thread:
>
> http://groups.google.com/group/comp.lang.idl-pvwave/browse_f rm/thread...
>
> (or search for "Local max filter" in this newsgroup)
>
> The stuff I found there worked very nicely for me as I recall.
>
> Jeff

Thanks Guys.
Cheers

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