How to use linear interpolation?

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Nicolas Perillo 2017-1-19

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https://ww2.mathworks.cn/matlabcentral/answers/321002-how-to-use-linear-interpolation

评论： Nicolas Perillo 2017-1-19

Hello everyone. I have a matrix that contains a pairs (pixel coordinates), for example M = [51,2 ; 50,2 ; 50,3 ; 51,2 ; 50,2 ; 50,1 ; 51,2 ; 52,4 ; 50,3], size(M) 9x2. The idea is that these pixels models a curve/contour extracted by a picture.

My problem is to use linear interpolation to obtain a new set of pairs of pixel coordinates such that the curve/contour is divided evenly in X segments, let's suppose X=12 segments.

In the example I'll have that each segment has a length of 9/12=0.75, this means I need to save 12 pixels starting from the position (51,2), ending at (50,3) with a rest of 10 pixels inside this interval placed "equally" with a distance of 0.75 that follow the curve/contour.

It seems impossible to obtain, save and display this new set of points because MATLAB works only with integer values. Notice that after this step, I need to use the new set of pixel coordinates to implement other functionalities (I don't need to display them and stop).

Does anyone knows a possible solution to my problem? Are there any functions that allow to use decimal coordinates (like cartesian axis)?

Thank you so much in advance.

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Jan 2017-1-19

I cannot imagine what "because MATLAB works only with integer values" means. Of course Matlab works with floating point values also. The coordinates can be floating point values without any problems. Only the indices of arrays must be integer, but this does not matter here at all. Do I understand correctly, that you want to obtain a [12 x 2] matrix by interpolation from your [9 x 2] matrix? If you claim, that the segements have a length of 0.75 - what does this mean? 0.75 in which units? I seems like you confuse the value of the elemts with the index.

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Answer 1

Jan 2017-1-19

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/321002-how-to-use-linear-interpolation#answer_251156

编辑：Jan 2017-1-19

在 MATLAB Online 中打开

M  = [51,2 ; 50,2 ; 50,3 ; 51,2 ; 50,2 ; 50,1 ; 51,2 ; 52,4 ; 50,3];
L  = size(M, 1);
MM = interp1(1:L, M, linspace(1, L, 12));

This does not consider this part of your question:

 In the example I'll have that each segment has a length of 9/12=0.75, 
 this means I need to save 12 pixels starting from the position (51,2),
 ending at (50,3) with a rest of 10 pixels inside this interval placed
 "equally" with a distance of 0.75 that follow the curve/contour.

because I do not understand its meaning.