generate a 3d scatter plot with z-support lines / pin plot / needle plot ...

Question

Andres 2024-12-10，11:02

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2171921-generate-a-3d-scatter-plot-with-z-support-lines-pin-plot-needle-plot

评论： Star Strider 2024-12-11，13:54

I'd like to plot scattered 3d data. To enhance readability, I want to add support lines in z-direction ("needles") to the data points with matching colors, see the image below.

Is there a specific name for such a plot?

To generate the chart, I used the code below with a for loop. I wonder if you have ideas how to simplify the code.

X = rand(20, 3);
f = figure;
hsc = scatter3(X(:,1),X(:,2),X(:,3), 20, X(:,3));
cmap = colormap('cool');
axis tight
xlabel("x"), ylabel("y"), zlabel("z")
title('needle plot')
box on
hold on
% draw support lines ("needles")
zlo = zlim*[1;0];
c_inter_fun = @(x) ...
    interp1(linspace(zlo, zlim*[0;1], length(cmap)).' , cmap, x);
for k = 1:numel(hsc.XData)
    plot3(hsc.XData(k)*[1 1], ...
        hsc.YData(k)*[1 1], ...
        [zlo, hsc.ZData(k)], ...
        Color=c_inter_fun(hsc.ZData(k)));
end

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Answer 1

Star Strider 2024-12-10，11:24

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See if the stem3 function will do what you want.

You will probably still have to use a loop of you want the individual stems and markers to be different colours, since the stem plots do not offer those options.

X = rand(20, 3);

f = figure;

hsc = stem3(X(:,1),X(:,2),X(:,3));

cmap = colormap('cool');

axis tight

xlabel("x"), ylabel("y"), zlabel("z")

title('needle plot')

box on

cm = cool(size(X,1));

f = figure;

hold on

for k = 1:size(X,1)

hsc = stem3(X(k,1),X(k,2),X(k,3), 'filled', Color=cm(k,:));

end

hold off

cmap = colormap('cool');

axis tight

xlabel("x"), ylabel("y"), zlabel("z")

title('needle plot')

box on

grid on

view(-27,30)

% hold on

% draw support lines ("needles")

% zlo = zlim*[1;0];

% c_inter_fun = @(x) ...

% interp1(linspace(zlo, zlim*[0;1], length(cmap)).' , cmap, x);

% for k = 1:numel(hsc.XData)

% plot3(hsc.XData(k)*[1 1], ...

% hsc.YData(k)*[1 1], ...

% [zlo, hsc.ZData(k)], ...

% Color=c_inter_fun(hsc.ZData(k)));

% end

.

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Star Strider 2024-12-10，15:59

编辑：Star Strider 2024-12-10，21:22

在 MATLAB Online 中打开

Using:

cmap = cool(size(X,1));

automatically interpolates to create individual colours for each row of ‘X’. This just makes the assignments easier.

Wiith respect to shorter colormaps, the interpolation would be the same, if you are interpolating. I characteristically limit colormaps to the number of elements in a particular vector, unless I know that I am dealing with values on a continuum or that is liikely to change.

It probably does not make any real difference, proviiding that there are enough rows in the ‘cmap’ variable to account for all the possible colours in the colormap.

EDIT — (10 Dec 2024 at 21:22)

It occurred to me later that the interpolation could be siimpliified to this by sorting X(:,3) in the interp1 call.

For that to work, ‘cmap’ has to have the same row size as ‘X’, since interp1 requires that—

X = rand(20, 3);

cmap = cool(size(X,1));

cm = interp1(sort(X(:,3)), cmap, X(:,3));

figure

axis tight

hold on

for k = 1:size(X,1)

stem3(X(k,1),X(k,2),X(k,3), Color=cm(k,:));

end

xlabel("x"), ylabel("y"), zlabel("z")

title('needle plot')

box on

grid on

view(-27,30)

.

Andres 2024-12-11，13:08

编辑：Andres 2024-12-11，13:08

在 MATLAB Online 中打开

If you just want to sort the colormap values along the z-value, you don't need to interpolate.

Two sorts

[~, si] = sort(X(:,3));
[~, si] = sort(si);
cm = cmap(si,:);

or one unique

[~, ~, si] = unique(X(:,3));
cm = cmap(si,:);

would do.

As I want to link the colormap values linearly to the z-value, the explicit interpolation seems unavoidable.

Star Strider 2024-12-11，13:54

Noted.

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Answer 2

Jacob Mathew 2024-12-10，11:13

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2171921-generate-a-3d-scatter-plot-with-z-support-lines-pin-plot-needle-plot#answer_1555442

在 MATLAB Online 中打开

Hey Andres,

You can use stem3 to achieve the effect you want. Here is an example:

X = rand(20, 3);

figure;

hold on;

% Create stem plot (needles)

stem3(X(:,1), X(:,2), X(:,3), 'Color', 'k');

% Customize plot

colormap('cool');

axis tight;

xlabel('x');

ylabel('y');

zlabel('z');

title('Needle Plot');

box on;

view(45,45); % To view the plot from a angle since plot is not interactive below

You can refer to the documentation of stem3 below:

https://www.mathworks.com/help/releases/R2024b/matlab/ref/stem3.html

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Andres 2024-12-10，12:49

Thanks, see above.

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generate a 3d scatter plot with z-support lines / pin plot / needle plot ...

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