How to subtract a scatterplot object from a polyshape object
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In my app I am defining polyshapes that represent satellite scan regions on Earth. I know how to subtract polyshapes from each other, for example along coastlines. Now I have a set of scatterplots that represent things such as sea ice, that I also need to subtract from the polyshape scan regions, something like this:
The pink represents the satellite scan region, and the blue is the scatterplot. I need to subtract the scatterplot area from the polyshape scan region. I know scatterplots do not have "area" per se, but perhaps we can define a boundary?
Is there a way to convert a scatterplot to a polyshape? I have seen several discussions here on scatterplots, but nothing quite like this situation. The closest I have come is this answer:
Thanks!
采纳的回答
Walter Roberson
2025-4-8
0 个投票
You can retrieve the XData and YData from the scatter plot, and pass the resulting points to boundary or alphaShape to trace around the outside of the set of points. This will give you a refined set of points that you can use to create another polyshape that you can then subtract from the original polyshape.
8 个评论
Walter Roberson
2025-4-8
You do not need to keep them well-ordered to use boundary() or (more likely) alphaShape()
Unless what you are talking about is
xd = HANDLE.XData;
yd = HANDLE.YData;
xyd = rmmissing([xd(:), yd(:)]);
shp = alphaShape(xyd);
Walter Roberson
2025-4-8
What is wrong with using rmmissing to strip out the fluff?
If you must use isnan then
xd = HANDLE.XData;
yd = HANDLE.YData;
mask = isnan(xd) | isnan(yd);
xd(mask) = [];
yd(mask) = [];
shp = alphaShape(xd, yd);
but rmmissing is a more compact way of removing nan.
Walter Roberson
2025-4-8
There are a large number of holes in data patches formed from scattered points. Even if you restrict your analysis to triangulations, every triangle created is a "hole"
Kurt
2025-4-9
Walter Roberson
2025-4-10
Well you could do something like kmeans clustering and select each cluster and boundary() it individually.
... Now you just need a way of automatically determining the correct number of clusters...
Kurt
2025-4-10
更多回答（1 个）
peak
2025-4-1
编辑：Steven Lord
2025-4-1
0 个投票
The scatterplot is shown in blue, while the satellite scan region is shown in pink. The scatterplot area must be subtracted from the polyshape scan region. https://www.mathworks.com/matlabcentral/answers/472879-surface-from-scatter-3-plot
[SL: Removed link that appeared to be unrelated to the question.]
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