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How to restrict the angle a cylinder is defined over

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Jonathan Bird
Jonathan Bird 2018-4-17
回答： Star Strider 2018-4-17
If you have a cylinder generated by the following code how would you define is so that the cylinder is restricted to certain angles such as between 0 and pi, thanks
[x,y,z]=cylinder([0,7,7,0],100);
z([1,2],:)=0;
z([3,4],:)=0.1;
surf(x,y,z);
axis equal

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回答（2 个）

Matt J
Matt J 2018-4-17
编辑：Matt J 2018-4-17

One way,

    [x,y,z]=cylinder([0,7,7,0],100);
    z([1,2],:)=0;
    z([3,4],:)=0.1;
    [theta,rho] = cart2pol(x,y);
    keep=(theta<=pi & theta>=0) | rho==0;
    z(~keep)=nan;
    surf(x,y,z);
    axis equal
  2 个评论
Jonathan Bird
Jonathan Bird 2018-4-17
Thanks, the trouble is I want all the internal bit as well not just a ring at the edge

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Star Strider
Star Strider 2018-4-17

Another option:

[x,y,z]=cylinder([0,7,7,0],100);
cidx = 1:ceil(size(x,2)*(pi/(2*pi)));                   % Scale Column Index By Fractions Of ‘2*pi’
z([1,2],:)=0;
z([3,4],:)=0.1;

surf(x(:,cidx) ,y(:,cidx) ,z(:,cidx));
axis equal
shading interp

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