Problem with the rotated object shape

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....

Answer 1

[KSSV]

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') ;

[Radhika Bhagwat]

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]

Attach your code here...

[Radhika Bhagwat]

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]

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]

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]

Add

axis equal

at the end? And use

   xlim( [] )  ;  ylim( [] )  ;

to control the axes extent.