Set points that matches with a vector as NaN

Question

Philippe Corner 2021-8-12

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/897257-set-points-that-matches-with-a-vector-as-nan

评论： Philippe Corner 2021-8-17

采纳的回答： Dave B

var.mat

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load('var.mat')

scatter3(cy(:,1),cy(:,2),cy(:,3),10,'k','filled');hold on

scatter3(top(:,1),top(:,2),top(:,3),10,'r','filled');

scatter3(bot(:,1),bot(:,2),bot(:,3),10,'r','filled');

whos cy

Name Size Bytes Class Attributes cy 46057x4 1473824 double

cy is a 4 columns matrix, I would like to set all the values of cy(:,4) that matches with the positiones above top vector and below bot vector as NaN values.

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Answer 1

Dave B 2021-8-12

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/897257-set-points-that-matches-with-a-vector-as-nan#answer_765902

在 MATLAB Online 中打开

In this particular case, because they all have the same y value, you can do this quite easily with interp:

scatter3(cy(:,1),cy(:,2),cy(:,3),10,'k','filled');hold on
scatter3(top(:,1),top(:,2),top(:,3),10,'r','filled');
scatter3(bot(:,1),bot(:,2),bot(:,3),10,'r','filled');
ind = cy(:,4) < interp1(bot(:,1),bot(:,3),cy(:,1)) | ...
            cy(:,4) > interp1(top(:,1),top(:,3),cy(:,1));
cy(ind,4) = nan;
scatter3(cy(:,1),cy(:,2),cy(:,4),10,'m','filled');hold on

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Dave B 2021-8-12

编辑：Dave B 2021-8-12

在 MATLAB Online 中打开

var.mat

The way that i understood your problem was that you have top which contains x,y,z co-ordinates for a top, and bot which contains x,y,z co-ordinates for a bottom.

Looking at your data, it was clear that the y values were irrelevant: all of the values are the same plane.

So I used interp1 to find the relvant z value for each x value. The expression:

interp1(bot(:,1),bot(:,3),cy(:,1))

says to find the z co-ordinate of the bottom by interpolating, using the x cordinate in cy and the mapping of x to z established in bot.

Below I've attached the result (I had to re-include the file): you can see that the values of cy(:,4) which are above and below top and bot have been removed.

load('var.mat')

scatter3(cy(:,1),cy(:,2),cy(:,3),10,'k','filled');hold on

scatter3(top(:,1),top(:,2),top(:,3),10,'r','filled');

scatter3(bot(:,1),bot(:,2),bot(:,3),10,'r','filled');

ind = cy(:,4) < interp1(bot(:,1),bot(:,3),cy(:,1)) | ...

cy(:,4) > interp1(top(:,1),top(:,3),cy(:,1));

cy(ind,4)=nan;

scatter3(cy(:,1),cy(:,2),cy(:,4),10,'m','filled');hold on

Philippe Corner 2021-8-12

Thank you very much for your help. And this approah using interp1 is very interesting idea to solve this task.

Best wishes!

Philippe Corner 2021-8-17

Hi Dave, this quiestion is very similar tham this one, but im confused about how to use it for all X, Y, Z positons. If you can give a hand it would be highly appreciated! https://it.mathworks.com/matlabcentral/answers/1413272-how-to-change-the-c-values-that-matches-a-3-coordinates-position-condition

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