How to plot coordinate data to appear solid with lighting effect?

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jf 2021-10-1

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评论： jf 2021-10-2

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I have quite delicate problem.

In the for loop I am plotting these circles using

plot3(x,y,z)

so after number of iteration it make this body of a certain shape.

I was searching everywhere but is it possible to plot these points to look more like solid/surface with lighting like as in the example below

The problem is that quite often these surfaces will cross itself like in the example here

so I also need to setup opacity of the resulting surface to see through.

I cannot provide any data because they are huge, but I would be gratefull for similar problem because I tried everything.

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Answer 1

Kevin Holly 2021-10-1

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编辑：Kevin Holly 2021-10-1

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There may be a better way doing it. Here is my attempt:

x1 = 0;

x2 = 0;

y1 = -.8; % value based on angle of 25 degrees

y2 = .8; % value based on angle of 25 degrees

eccentricity = .78;

numPoints = 300; % Less for a coarser ellipse, more for a finer resolution.

% Make equations:

a = (1/2) * sqrt((x2 - x1) ^ 2 + (y2 - y1) ^ 2);

b = a * sqrt(1-eccentricity^2);

t = linspace(0, 2 * pi, numPoints); % Absolute angle parameter

X = a * cos(t);

Y = b * sin(t);

% Compute angles relative to (x1, y1).

angles = atan2(y2 - y1, x2 - x1);

x = (x1 + x2) / 2 + X * cos(angles) - Y * sin(angles);

y = (y1 + y2) / 2 + X * sin(angles) + Y * cos(angles);

figure

subplot (2,2,1)

plot3(x,y,zeros(size(y)))

hold on

plot3(x,y,0.5*ones(size(y)))

hold on

plot3(x,y,ones(size(y)))

axis equal

X = [x x x];

Y = [y y y];

Z = [zeros(size(y)) 0.5*ones(size(y)) ones(size(y))];

T=delaunayTriangulation(X',Y',Z');

% Generate solid object

subplot (2,2,2)

% hObj = tetramesh(T,ones(size(T)),'FaceAlpha',0.5,'EdgeColor','none','FaceLighting','phong');

hObj = tetramesh(T,ones(size(T)),'FaceAlpha',0.5,'EdgeColor','none','FaceLighting','gouraud');

light('Position',[-10 -10 10],'Style','local')

light('Position',[-10 -10 -10],'Style','local')

subplot (2,2,3)

% hObj = tetramesh(T,ones(size(T)),'FaceAlpha',0.5,'EdgeColor','none','FaceLighting','phong');

hObj = tetramesh(T,ones(size(T)),'FaceAlpha',0.2,'EdgeColor','none','FaceLighting','gouraud');

light('Position',[-10 -10 10],'Style','local')

light('Position',[-10 -10 -10],'Style','local')

subplot (2,2,4)

% hObj = tetramesh(T,ones(size(T)),'FaceAlpha',0.5,'EdgeColor','none','FaceLighting','phong');

hObj = tetramesh(T,ones(size(T)),'FaceAlpha',0.1,'EdgeColor','none','FaceLighting','gouraud');

light('Position',[-10 -10 10],'Style','local')

light('Position',[-10 -10 -10],'Style','local')

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jf 2021-10-1

Thank you for your attempt, but this one will fail for cases with iteself colliding surfaces

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Answer 2

Kelly Kearney 2021-10-1

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The following example shows a relatively simple way to create patch surfaces that connect each circle to the adjacent one (assuming that all of your circles include the same number of vertices).

% Coordinates for 3 simple test circles

nv = 50;

th = linspace(0,2*pi,nv);

r = [10; 5; 6; 8];

z = [0; 1; 2; 1.5];

x = r.*cos(th);

y = r.*sin(th);

z = zeros(size(x))+z;

x = x'; y = y'; z = z';

% Calculate surface patch coordinates by connecting each

% circle to the adjacent one

ncirc = size(x,2);

[c0,v0] = ndgrid(1:ncirc-1, 1:nv-1);

cidx = c0(:) + [0 1 1 0 0];

vidx = v0(:) + [0 0 1 1 0];

idx = sub2ind(size(x), vidx, cidx);

xs = x(idx');

ys = y(idx');

zs = z(idx');

% Plot

hp = patch(xs, ys, zs, 'b');

view(3);

set(hp, 'facealpha', 0.8, 'edgecolor', 'none');

hold on;

plot3(x,y,z, 'k');

camlight

You'll probably have to play around with lighting and transparency, but this should be robust even if your circles overlap or reverse direction, as I've shown with the last two in this example.

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jf 2021-10-2

Thank you, provided code in R2016 does not run, but its not an issue since I got the idea how you approach the problem. Once I manage to tackle with on my own, I am accepting your answear.

jf 2021-10-2

This is indeed an improvement

but the problem with this approach is that the lighting is effectively not seen because the step size between circles is (and must be) small so calling camplight in each iteration produce nothing for the whole 'object'.

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How to plot coordinate data to appear solid with lighting effect?

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