Find turning point in data

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Hg
Hg 2015-10-22
评论： Firas Guechchati 2020-10-20
How to get data gradient and how to locate significant changes of the gradient? I'm trying to locate the first "turning point" of the plot below. Other turning points can be ignored.
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Walter Roberson
Walter Roberson 2015-10-22
How can you tell that it is a turning point? The part to the left of it is not linear so the part to the left of it has places where the slope changes: why are they not turning points?
Hg
Hg 2015-10-22
It's hard. May be by thresholding.

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Image Analyst
Image Analyst 2015-10-22
Points like that are often found using a triangle thresholding method. I think there's one in the File Exchange. Basically it draws a line from the peak to the tail and then draws perpendicular lines from that hypotenuse line to the curve. The longest perpendicular line from the hypotenuse to the curve indicates the "corner" of the curve. Maybe that will work for you.
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Image Analyst
Image Analyst 2020-10-19
Your data and your signal are the same thing in that case. The index is the element of the data where your threshold is. Why doesn't it work for you? You can't personally message me but I monitor this forum very closely.
Please start your own thread and attach your data or image, and code. Let's not keep bugging the original poster HG with emails about activity on this discussion.
Firas Guechchati
Firas Guechchati 2020-10-20
sorry my last post
this is the thread
https://de.mathworks.com/matlabcentral/answers/613781-i-plotted-this-and-i-want-to-measure-the-length-and-analyze-the-section-of-this-plot

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