How to create a surface of revolution from the 2D perimeter?

Question

Martina Clairand 2021-4-29

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https://ww2.mathworks.cn/matlabcentral/answers/817355-how-to-create-a-surface-of-revolution-from-the-2d-perimeter

评论： Martina Clairand 2021-4-29

采纳的回答： DGM

IM.jpg

Hello,

I would like to transform the pear-shaped object in the attached image to a 3D pear.

For this I first tried to obtain the perimeter of the object via this code:

%% To detect the object

E = imbinarize(IM);

etiqueta=bwlabel(E);

object=(etiqueta==1);

figure (1)

imshow(object)

%% To find the figure contour

[B,L] = bwboundaries(object);

boundary=B{1};

figure (2)

plot(boundary(:,2), boundary(:,1), 'k', 'LineWidth', 2)

Then I was planning to use "cylinder" to revolve the perimeter but I didn't manage to obtain what I expected. Do you have an idea on how I can convert my 2D pear-shaped object into a 3D pear?

Thank you in advance for your help!

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Answer 1

DGM 2021-4-29

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There are probably plenty of ways to do this, but the basic idea is that you need to know the axis of rotation and you need a function describing the radius of the object. Since your boundary is a closed curve, you have a surplus of information. In this example, I just chose to use the upper half of the curve, but you could use the lower half or average them or something.

IM = imread('pear.jpg');
E = imbinarize(IM);
object=bwareafilt(E,1); % this can be done with bwareafilt() if you have it
imshow2(object,'invert')
% i guess the object is already centered at y=140
% select the upper curve
[~,upper] = max(object);
xextent = [find(upper>1,1,'first') find(upper>1,1,'last')];
upper = 140-upper(upper>1); % trim off invalid radii
upper([1 end]) = 0; % close the curve
% in order to orient the cylinder, reorder the axes
[Y Z X] = cylinder(upper,40);
% by default, Z is normalized, so it has to be denormalized
surf(X*diff(xextent)+xextent(1),Y,Z)
axis equal
shading flat