Removing negative values of 3d data

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Nathan Mu 2022-4-17

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https://ww2.mathworks.cn/matlabcentral/answers/1698670-removing-negative-values-of-3d-data

评论： Tim Albertsson 2024-2-16

Hello, I have a diagram where I want to get rid of the lower portion (the points which have negative z value) so I can use scatteredInterpolant on it. How would I do this?

The points are stored in a 3D array with index (1,1,1) being an x-value, (1,1,2) being the corresponding y value and (1,1,3) being the corresponding z value.

Thanks!

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Torsten 2022-4-18

编辑：Torsten 2022-4-18

This answer should be helpful in your case:

https://de.mathworks.com/matlabcentral/answers/384291-3d-surface-plot-out-of-points

Or you could just replace the data points with negative z by NaN - they will not appear in the plot afterwards.

Nathan Mu 2022-4-18

Okay thanks!

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Chunru 2022-4-18

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1698670-removing-negative-values-of-3d-data#answer_945030

编辑：Chunru 2022-4-19

在 MATLAB Online 中打开

ggv.mat

x = load("ggv.mat");

GGV = x.GGV;

figure

surf(GGV(:,:,2), GGV(:,:,3), GGV(:,:,1), 'EdgeColor', 'none');

xlabel('x'); ylabel('y')

figure

% to demonstrate limit works for X data (Z in the plot)

surf(GGV(:,:,2), GGV(:,:,3), max(GGV(:,:,1), -20), 'EdgeColor', 'none'); % -20 and above

xlabel('x'); ylabel('y')

% The number of points for z<0

sum(GGV(:, :, 3) < 0, 'all')

ans = 0

min(GGV(:, :, 3), [], 'all')

ans = 0

figure

% limit z data here will not make no change since no z is less than 0

surf(GGV(:,:,2), max(GGV(:,:,3), 0), GGV(:,:,1), 'EdgeColor', 'none');

xlabel('x'); ylabel('y')

figure

% limit GGV(:,:,1)

surf(GGV(:,:,2), GGV(:,:,3), max(GGV(:,:,1), 0), 'EdgeColor', 'none');

xlabel('x'); ylabel('y')

zlim([-80 20])

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Chunru 2022-4-19

See above update.

Tim Albertsson 2024-2-16

Hi! How did you get the GGV points from the start? I'm trying to make my own script for this and I've gotten the max lat and lon accelerations for the different speeds but not the full (GG "elipse").

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更多回答（1 个）

Chunru 2022-4-18

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1698670-removing-negative-values-of-3d-data#answer_944895

在 MATLAB Online 中打开

% Your data
data = randn(357, 177, 3);
% limit to 0
data(:, :, 3) = max(data(:, :, 3), 0);   % to limit the surface up to 0
% You may also want to try nan (depending on how you plot the data)
idx = data(:, :, 3) < 0;
data(idx, 3) = nan;

I wanted to get rid of the points which have z<0 so I could use it as a function. So I would input lateral acceleration and speed and it would give out a longitudinal acceleration. However with the GGV array as is, there are two different values of long acc for any given lat acc and speed, so it isn't a function which can be put into scatteredInterpolant.

The issue may actually be due to how the array is structured. So I'll try to restructure it as a 2D matrix with three columns (x,y,z) and see how that pans out.