how to use polyarea

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louis rassinfosse 2016-4-28

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评论： louis rassinfosse 2016-4-29

采纳的回答： Image Analyst

hello,

I would need some help using the 'polyarea' function..

lets say: x=[1.5 1.25]; y=[570 363];

Plot(x,y) gives me a clear line, when is use area(x,y) I can visualize the area I want to calculate, but when I use polyarea(x,y), the answer is always 0 ... Can anyone help me out ?

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John D'Errico 2016-4-28

What area is it that you want to calculate? Be clear, as it is difficult for us to know what you are visualizing. The crystal ball can be so foggy.

For example, what if the line crosses the x-axis?

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Answer 1

Image Analyst 2016-4-29

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You need at least 3 points to have an area. Maybe you want the area below. Try this:

   x=[1.5 1.25]; 
   y=[570 363];
   xTrap = [x(1), x(1), x(2), x(2)]
   yTrap = [0, y(1), y(2), 0]
   patch(xTrap, yTrap, 'r.-', 'LineWidth', 2);
   grid on;
   theArea = polyarea(xTrap, yTrap)