Spherical Patch in 3D

Question

Chris Dan 2022-3-29

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1683214-spherical-patch-in-3d

评论： Chris Dan 2022-3-29

采纳的回答： Chris Dan

在 MATLAB Online 中打开

Hello,

I am trying to make a 3d spherical segment. I am having problems with the atan2 function. in 2D my code is

clear all; close all;
p = linspace(-1/2,1/2,200);
[X,Y] = meshgrid(p,p); % box mesh
R = p(size(p,2))/2;
r = R/1.5;
alpha = deg2rad(45);
theta = atan2(Y,X);
f = figure('visible','on');
active = (X.^2 + Y.^2  <= R^2) & (X.^2 + Y.^2 >= r^2);
plot(X(active),Y(active),'o','MarkerFaceColor','blue');
active = (X.^2 + Y.^2  <= R^2) & (X.^2 + Y.^2 >= r^2) & (abs(theta)< alpha); 
hold on
plot(X(active),Y(active),'o','MarkerFaceColor','red');

here every thing is as I want(the red patch) ,but when I try to make the same patch in 3D, I am getting getting the wrong shape.

here is my code:

clear all; close all;
p = linspace(-1/2,1/2,100);
[X,Y,Z] = meshgrid(p,p,p); % box mesh
R = p(size(p,2))/2;
r = R/1.5;
alpha = deg2rad(45);
f = figure('visible','on');
theta = atan2(Z,X);
active = (X.^2 + Y.^2 + Z.^2  <= R^2) & (X.^2 + Y.^2 +Z.^2 >= r^2);
plot3(X(active),Y(active),Z(active),'o','MarkerFaceColor','blue');
active = (X.^2 + Y.^2 + Z.^2 <= R^2) & (X.^2 + Y.^2 +Z.^2 >= r^2) & (abs(theta) <= alpha); 
hold on
plot3(X(active),Y(active),Z(active),'o','MarkerFaceColor','red');
saveas(f,'3d_patch','fig')

Can anyone tell me what is wrong? I figured it out to be theta...

Does any one knows how to take correct angle

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Answer 1

Chris Dan 2022-3-29

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1683214-spherical-patch-in-3d#answer_929554

在 MATLAB Online 中打开

I found out the answer

clear all; close all;
p = linspace(-1/2,1/2,100);
[X,Y,Z] = meshgrid(p,p,p); % box mesh
R = p(size(p,2))/2;
r = R/1.5;
alpha = deg2rad(45);
f = figure('visible','on');
theta = atan2(sqrt(X.^2+Y.^2),Z);
active = (X.^2 + Y.^2 + Z.^2  <= R^2) & (X.^2 + Y.^2 +Z.^2 >= r^2);
plot3(X(active),Y(active),Z(active),'o','MarkerFaceColor','blue');
active = (X.^2 + Y.^2 + Z.^2 <= R^2) & (X.^2 + Y.^2 +Z.^2 >= r^2) & (abs(theta) <= alpha); 
hold on
plot3(X(active),Y(active),Z(active),'o','MarkerFaceColor','red');
saveas(f,'3d_patch','fig')