Plot envelope of a grassy plot

2016 6 11
3 个回答
更新时间：2016 6 14
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Hi all, I have a graph which looks very grassy. What I want is the following (see picture). I have a grassy graphy (blue line), but I want the envelope which clearly shows the peaks of the graph (red line - this line is drawn in paint). A group of peaks may added to 1 group of peak. I have tried the following in matlab, without success: - smooth; - basic tool of curve fitting; - Hilbert transform; - polyfit; - Toolbox Ezyfit; butterworth function.
The problem is that I either get too many peaks, or the envelope does not really fit.
Any suggestions how to deal with this? Thanks in advance!

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回答（3 个）

Chad Greene
Chad Greene 2016-6-11

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Do you have the Signal Processing toolbox? If so, the envelope function makes is pretty easy to use.

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André
André 2016-6-11
Thanks for your answer. I tried the envelope function, also with 'peak' to detect the peak envelope. However, it is still too grassy ..but it is sort of in the right direction ..

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Image Analyst
Image Analyst 2016-6-11

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Another option is sgolayfilt(). They all give different looks and it just depends on what "look" you're looking for.
Image Analyst
Image Analyst 2016-6-11

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Maybe you can use findpeaks(). There are lots of options for specifying which peaks you want to detect and which you want to ignore. Then, once you've found the peaks, use linspace() to draw lines in between the peaks to fill out the array so that you have a value at every index.

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André
André 2016-6-12
I tried your suggestion, but I keep getting the following error:
Error using findpeaks
Expected X to be increasing valued.
However, there are many many X-values that are the same (and not increasing), and I do not want to delete it (manually), because I will probably lose too much information for my purpose.
Any idea how to proceed?
Image Analyst
Image Analyst 2016-6-12
编辑：Image Analyst 2016-6-13
We can't really help you unless you supply your X and x and y values and code.
André
André 2016-6-13
Please find attached. The first row is x and second row y.
Image Analyst
Image Analyst 2016-6-13
Please supply the code you used that generated the error and I'll try it tomorrow.
André
André 2016-6-13
I tried the following with findpeaks():
  1. findpeaks(y); because I want find the peaks of y and then proceed as you suggested
  2. findpeak(x,y); then I get the error message as above. In addition, I did not provide an X (only x and y as the file attached).
For point 1, I am able to detect the peaks, but there is a shifting in the x-axis and y-axis.
How to proceed from here?
André
André 2016-6-14
I also tried stem() instead of plot() and then envelope, but without success still.

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André
André
2016-6-11

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2016-6-14

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