results of 2 plots seem to be overlapping each other

i have generated a virtual 3D cube. after that i am asked to capture an image of that virtual cube in at 4 meters distance and 30 degree tilted. i am able to do that too. but in both cases 2 plots of 2 images are supposed to be generated. but the result of the second plotting seems to be overlapping the previous plotting image. if i give a 'break' command in between these 2 code then i can see the previous plot again. but if i delete the break command then i can only see the 2nd plot. please let me know how to solve this.

    %question 6(3)(a)
      %generating a virtual 3D cube 
      %%Generating 3D calibration pattern: 
      %%Pw holds 32 points on two surfaces (Xw = 1 and Yw = 1) of a cube 
      %%Values are measured in meters.
      %%There are 4x4 uniformly distributed points on each surface.

      cnt = 1;

      %%plane : Xw = 1
      Pw = zeros(4,3);%preallocating Pw

      for i=0.2:0.2:0.8,
       for j=0.2:0.2:0.8,
         Pw(cnt,:) = [1 i j];
         cnt = cnt + 1;

       end
      end

      %%plane : Yw = 1

      for i=0.2:0.2:0.8,
       for j=0.2:0.2:0.8,
         Pw(cnt,:) = [i 1 j];
         cnt = cnt + 1;
       end
      end

      N = cnt;

      %%plot3(Pw(:,1), Pw(:,2), Pw(:,3), '+');

      %%Virtual camera model 

       %%Extrinsic parameters : R = RaRbRr

      gamma = 40.0*pi/180.0;
      Rr = [ [cos(gamma) -sin(gamma) 0];
             [sin(gamma) cos(gamma)  0];
             [  0          0         1]; ];

      beta = 0.0*pi/180.0;

      Rb = [ [cos(beta) 0 -sin(beta)];
             [0         1       0];
             [sin(beta) 0  cos(beta)]; ];

      alpha = -120.0*pi/180.0;
      Ra = [ [1      0                0];
             [0   cos(alpha)  -sin(alpha)];
             [0   sin(alpha)   cos(alpha)]; ];

      R = Ra*Rb*Rr;

      T = [0 0 4]';

      %%Intrinsic parameters

      fa = 0.016;
      Ox = 256;
      Oy = 256;

      Sx = 0.0088/512.0;
      Sy = 0.0066/512.0;

      Fx = fa/Sx;
      Fy = fa/Sy;

      %%asr is the aspect ratio
      asr = Fx/Fy;

      %%Generate Image coordinates

      %%surface Xw = 1
      cnt = 1;
      Pc = zeros(16,3);
      n=length([(Ox - Fx*Pc(cnt,1)/Pc(cnt,3)) (Oy - Fy*Pc(cnt,2)/Pc(cnt,3))]);
       p=zeros(16,n);

      for cnt = 1:1:16,
         Pc(cnt,:) = (R*Pw(cnt,:)' + T)';
         p(cnt,:)  = [(Ox - Fx*Pc(cnt,1)/Pc(cnt,3)) (Oy - Fy*Pc(cnt,2)/Pc(cnt,3))];
      end
      plot(p(:,1), p(:,2), 'r+');
      axis([0 512 0 512]);
      grid;
      hold;

      %%surface Yw = 1
      for cnt = 17:1:32,
         Pc(cnt,:) = (R*Pw(cnt,:)' + T)';
         p(cnt,:)  = [(Ox - Fx*Pc(cnt,1)/Pc(cnt,3)) (Oy - Fy*Pc(cnt,2)/Pc(cnt,3))];
      end
      plot(p(17:32,1), p(17:32,2), 'g+');
      %%plot3(Pc(:,1), Pc(:,2), Pc(:,3), '+');
      grid;
  %3D point generated from the 3D virtual cube
  xvals = Pc(:,1);
  yvals = Pc(:,2);
  zvals = Pc(:,3);
  %..6.3.b
  cnt1 = 1;

%%plane : Xw = 1
Pw1 = zeros(4,3);%preallocating Pw

for i=0.2:0.2:0.8,
 for j=0.2:0.2:0.8,
   Pw1(cnt1,:) = [1 i j]; 
   cnt1 = cnt1 + 1;

   end
  end

%%plane : Yw = 1

for i=0.2:0.2:0.8,
 for j=0.2:0.2:0.8,
   Pw1(cnt1,:) = [i 1 j];
   cnt1 = cnt1 + 1;
 end
end

N1 = cnt1;

%%plot3(Pw(:,1), Pw(:,2), Pw(:,3), '+');

%%Virtual camera model 

   %%Extrinsic parameters : in a certain pose where R = 30 degree and T is 4 meters 

Rb1 = 30.0*pi/180.0;

Tb = [0 0 4]';

%%Intrinsic parameters

fb = 0.016;
Ox = 256;
Oy = 256;

Sx = 0.0088/512.0;
Sy = 0.0066/512.0;

Fxb = fb/Sx;
Fyb = fb/Sy;

%%asr is the aspect ratio
asrb = Fxb/Fyb;

%%Generate Image coordinates

%%surface Xw = 1
cnt1 = 1;
Pc1 = zeros(16,3);
n1=length([(Ox - Fxb*Pc1(cnt1,1)/Pc1(cnt1,3)) (Oy - Fyb*Pc1(cnt1,2)/Pc1(cnt1,3))]);
 p1=zeros(16,n1);

for cnt = 1:1:16,
   Pc1(cnt,:) = (Rb1*Pw1(cnt1,:)' + Tb)';
   p1(cnt,:)  = [(Ox - Fxb*Pc1(cnt1,1)/Pc1(cnt1,3)) (Oy - Fyb*Pc1(cnt1,2)/Pc1(cnt1,3))];
end
plot(p1(:,1), p1(:,2), 'r+');
axis([0 512 0 512]);
grid;
hold;

%%surface Yw = 1
for cnt1 = 17:1:32,
   Pc1(cnt1,:) = (Rb*Pw1(cnt1,:)' + Tb)';
   p1(cnt1,:)  = [(Ox - Fxb*Pc1(cnt1,1)/Pc1(cnt1,3)) (Oy - Fyb*Pc1(cnt1,2)/Pc1(cnt1,3))];
end
plot(p1(17:32,1), p1(17:32,2), 'g+');
%%plot3(Pc1(:,1), Pc(:,2), Pc(:,3), '+');
grid;