inpolygon usage with big matrices or faster function

Question

Ahmet Hakan UYANIK 2022-11-9

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https://ww2.mathworks.cn/matlabcentral/answers/1847343-inpolygon-usage-with-big-matrices-or-faster-function

评论： Ahmet Hakan UYANIK 2022-11-10

Hello,

I have a matrix for latitudes with the size of 12200x6700 and longitudes with same size as well. I have a polygon of a river as well to check if the points are inside the polygon. However when I do

in = inpolygon(longitude,latitude,Poly.Lon,Poly.Lat);

it never ends.

If I check it by each column with for loop(6700 times), it again takes so much time.

Is there any way to fasten this single line. Like maybe using parfor by seperating the longitude and latitude?

Thanks in advance, Cheers

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Answer 1

Bruno Luong 2022-11-9

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https://ww2.mathworks.cn/matlabcentral/answers/1847343-inpolygon-usage-with-big-matrices-or-faster-function#answer_1095598

Try this https://fr.mathworks.com/matlabcentral/fileexchange/27840-2d-polygon-interior-detection?s_tid=srchtitle

At some point it was 10 time faster than MATLAB stock function.

But you can start to discard points outside the conves hull first as Matt suggests then refine with this non convex polygonal function.

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Ahmet Hakan UYANIK 2022-11-10

Regarding big size of matrices, this tool works way more faster than MATLAB stock function(even much more faster than 10 times :) Thanks in advance.

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Answer 2

Matt J 2022-11-9

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https://ww2.mathworks.cn/matlabcentral/answers/1847343-inpolygon-usage-with-big-matrices-or-faster-function#answer_1095583

编辑：Matt J 2022-11-9

Is it a convex polygon? There are much faster alternatives to inpolygon for convex polygons,e.g.,

https://www.mathworks.com/matlabcentral/fileexchange/10226-inhull?s_tid=srchtitle

Even if it is not a convex polygon, perhaps you can frst discard points that are not in the convex hull of the polygon, thereby reducing the amount of work that inpolygon needs to do.