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 Calculating area under a complicated curve

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Flopi Posted - 03/16/2016 : 09:31:06 AM
Hello all,
I would like to calculate an area with ORIGIN. The issue is that the data I have look like the following image




There are some x-position where we have 2 (or more) y-values. My question is then twofold : is the integrate operation in ORIGIN calculating the proper area under my curve (i.e. the area enclosed by the curve). If not, how shoud I proceed to obtain the proper area ?
Thanks a lot for your help
6   L A T E S T    R E P L I E S    (Newest First)
Chris D Posted - 03/17/2016 : 12:04:34 PM
Hi,

Perhaps you can rearrange your data so that it follows a line shape as appears in your original data (which I simulated). There isn't too much else that can be done that does not require some manual work on your part to get a polgygon shape.

Thanks,
Chris Drozdowski
Originlab Technical Support
Flopi Posted - 03/17/2016 : 10:39:47 AM
Thank you for your answer. It's exactly what I need. I have however a last question. In my case, I don't have a clean curve as yours when I plot it. I have rather what is on the following image. The enclosing for the polygon follows this graph and is not quite I want...
Chris D Posted - 03/17/2016 : 10:01:17 AM
Hi,

Try this.

Follow the steps outlined in the screen shots below to enclose your data into a polygon area. you may have to adjust the steps based on your actual data but this will point you in the right direction.

Once you do that, you can go to the analysis menu and select Mathematics->Polygon Area to integrate the enclosed polygon.



Thanks,
Chris Drozdowski
Originlab Technical Support
Flopi Posted - 03/17/2016 : 04:57:44 AM
Thanks for your answers.
So if I understand correctly AmandaLu the integrate function is already doing the job without any additional correction ? Does the area has to be closed though (like your disk) ?
AmandaLu Posted - 03/17/2016 : 04:21:43 AM
Hi Flopi,

Analysis: Mathematics: Integrate can calculate such area. See image below:



Thanks,
Amanda
OriginLab Technical Service
Castiel Posted - 03/17/2016 : 04:05:42 AM
quote:
Originally posted by Flopi

Hello all,
I would like to calculate an area with ORIGIN. The issue is that the data I have look like the following image




There are some x-position where we have 2 (or more) y-values. My question is then twofold : is the integrate operation in ORIGIN calculating the proper area under my curve (i.e. the area enclosed by the curve). If not, how shoud I proceed to obtain the proper area ?
Thanks a lot for your help


I suppose you are looking for something equivalent to polyarea(X, Y) in MATLAB. Here it is:
OCMATH_API_MUST double ocmath_d_polygon_area(double* pX, double* pY, uint nSize)

It's available in Origin C though.

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