inpolygon counting points within holes

Question

Alan 2024-7-31，20:52

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2141886-inpolygon-counting-points-within-holes

评论： Alan 2024-7-31，21:37

采纳的回答： Aditya

matlabest.mat

在 MATLAB Online 中打开

Hello,

I am attempting to find whether points fall within areas on a map. I've decided to do this using inpolygon. I've been having trouble with areas with holes and I have no idea why. Here is an example:

load("matlabest.mat")

test2=polyshape(test)

test2 =

polyshape with properties: Vertices: [159x2 double] NumRegions: 1 NumHoles: 1

plot(test2)

As we can see from this shape, the point (-75.6,40.51) falls within the hole of this shape. Therefore, inpolygon should return 0. Let's test this:

inpolygon(-75.6,40.51,test(:,1),test(:,2))
ans = logical
   1

I really don't understand why this is happening, as my example here is almost identical to the example given in the literature for inpolygon, just on a larger scale. I thought it had something to do with the NaNs I inserted to split between the coordinates of the hole and the actual shape, but the example in the literature does the same thing, so I don't think its that. I'm not sure what else it could be, so could someone please help me out?

Thanks

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Answer 1

Aditya 2024-7-31，21:22

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https://ww2.mathworks.cn/matlabcentral/answers/2141886-inpolygon-counting-points-within-holes#answer_1493071

在 MATLAB Online 中打开

Hi Alan,

It seems that the data "test" contains NaN values somewhere which is creating the issue.

you could either use:

isInside = isinterior(test2, -75.6, 40.51);

or you can modify your code to use test2 directly:

inpolygon(-75.6,40.51,test2.Vertices(:,1),test2.Vertices(:,2))

Refer to the below MATLAB documentation to read more about "isinterior" function:

https://in.mathworks.com/help/matlab/ref/polyshape.isinterior.html

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Alan 2024-7-31，21:37

The NaN aren't causing the issue here, as the 2nd to last example given in this link show the NaNs working with holes. However, I didn't realize that isinterior works with polyshapes, so this fixed my issue, thanks

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