Problem with the rotated object shape

2016 8 17
1 个回答
更新时间：2018 10 3
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0 个投票

I have written a code for generating egg shape from ellipse using the model explained in the link below optimal shape of avian egg.The ellipse that i have generated is using normal parametric equations. x = a*cos(theta) y = b* sin(theta) Below is the figure of ellipse along with the egg shape generated by the model explained in the link above.
</matlabcentral/answers/uploaded_files/57944/ellipse%20and%20egg%20shape.jpg> next I tried to rotate the egg shape by angle pi/2 using transformation matrix; but this is what i get.
</matlabcentral/answers/uploaded_files/57945/rotated%20egg%20shape.jpg> My question is why am I not getting a proper egg shape in the rotated version?I get proper figure for an angle of pi.but not for any other angles .... pi/6,pi/3 etc....

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回答（1 个）

KSSV
KSSV 2016-8-17

0 个投票

I don't know how you have rotated the object/ geometry; I cannot even open the links you have given. You may consider the below code, which may help you.
clc; clear all ;
s = [-1 -1 ; -1 1 ; 1 1 ; 1 -1 ; -1 -1]' ; % draw square
plot(s(1,:),s(2,:),'r') ;
%%rotate the object
th = pi/4 ; % rotate by 45 degrees
R = [cos(th) -sin(th) ; sin(th) cos(th)] ; % rotation matrix
S = zeros(size(s)) ; % initialize rotated coordinates
for i = 1:size(s,2)
S(:,i) = R*s(:,i) ;
end
hold on
plot(S(1,:),S(2,:),'b') ;

6 个评论
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Radhika Bhagwat
Radhika Bhagwat 2016-8-17
thank you for the reply. yes I too have done the rotation using same method. but after rotation the egg shape that I get is a compressed version . Have tried to load the figures once again.
KSSV
KSSV 2016-8-17
Attach your code here...
Radhika Bhagwat
Radhika Bhagwat 2016-8-17
here is the code:
%%generating ellipse
a = 30;b=20;
etheta = [0:0.01:2*pi];
ex = a .*cos(etheta);
ey = b .* sin(etheta);
figure();plot(ex,ey);
%%getting egg shape from ellipse
newex = ex;
c0 = 1;c1 = 0.2;c2 =0; c3=0;
exdash = newex./a;
efun = c0+c1.*exdash+c2.*exdash.^2+c3.*exdash.^3;
newey = ey.*efun;
figure();plot(newex,newey,'color','red');
%%rotate egg shape by pi/2
ealpha = pi/2;
ec= cos(ealpha);es = sin(ealpha);
EQ = [ec -es;es ec];
enew = EQ*[newex;newey];
figure();plot(enew(1,:),enew(2,:));
KSSV
KSSV 2016-8-17
I think the code is working fine.....I calculated area of the egg, in both the cases it is same. I don't think there is any problem with rotated egg..
Radhika Bhagwat
Radhika Bhagwat 2016-8-17
so then why is it looking compressed? do i need to adjust the figure window size? cause doing that gives a proper view. but then do i have to keep adjusting the window size for every angle ?Below is the adjusted figure window displaying egg shape for pi/2;
William Chamberlain
编辑：William Chamberlain 2018-10-3
Add
axis equal
at the end? And use
xlim( [] ) ; ylim( [] ) ;
to control the axes extent.

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