Area of contor from Matrix

Question

Mad Gano 2023-1-13

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1893810-area-of-contor-from-matrix

评论： Mad Gano 2023-1-18

采纳的回答： Matt J

I have a matrix with 2 coordinates x, y and the force F

about 2 million rows (2M X 3)

I want to plot the contor of this data while F > 0.1 N.

after that I want to calculate the area of the contor.

I can't use the function "contour" because I don't have mesh data and I cant use meshgrid because the matrix is very large

Can any one help me :)

Thanks

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Matt J 2023-1-13

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1893810-area-of-contor-from-matrix#answer_1148425

编辑：Matt J 2023-1-13

在 MATLAB Online 中打开

Use scatteredInterpolant to resample the data on a grid,

S=scatteredInterpolant(x,y,F);
xg=linspace(min(x),max(x),500);
yg=linspace(min(y),max(y),500);
Fg=S({xg,yg});

and then use contour().

cm=contour(xg,yg,Fg',[0.1,0.1]);

meshgrid is irrelevant to the discussion. As demonstrated above, you don't need meshgrids of the x,y data to use contour(), but even if you were to do that, they wouldn't be that large.

4 个评论
显示 2更早的评论隐藏 2更早的评论

Adam Danz 2023-1-15

编辑：Adam Danz 2023-1-15

在 MATLAB Online 中打开

TestFile.mat

getContourLineCoordinates produces a table indicating the (x,y) coordinates and level for all contourlines along with a grouping variable that groups each contour line group. You can loop through the groups to compute the area for each contour line and then select the largest group.

File=load('TestFile.mat');
x=File.Matrix(:,1);
y=File.Matrix(:,2);
F=File.Matrix(:,3);
S=scatteredInterpolant(x,y,F);
xg=linspace(min(x),max(x),500);
yg=linspace(min(y),max(y),500);
Fg=S({xg,yg});
cm=contour(xg,yg,Fg',[0.01,0.01]);
T=getContourLineCoordinates(cm); % Get contour table
% loop through each contour group
groups = unique(T.Group);
areas = nan(size(groups)); 
for i = 1:numel(groups)
    idx = T.Group==i;
    areas(i) = polyarea(T.X(idx), T.Y(idx));
end
% Find the max area
[maxArea, maxidx] = max(areas)