Asymptote: maintain window size while changing POV in animation

Question

In every Asymptote animation example that I found (see e.g. here or here), the viewpoint is constant during the animation. I would like to make one which consists in a rotating viewpoint, the drawn objects being constant.

The following code works, but as you can see the resulting gif is unsteady. How can I avoid this?

size(10cm,10cm);
import graph3;
import grid3;
//import animation;
import animate;

settings.render=1;
animation A;
A.global=false;

real xmin=-2, xmax=2;
real ymin=-2, ymax=1.5;
real zmin=-2.5, zmax=2.5;

limits((xmin,ymin,zmin),(xmax,ymax,zmax));

unitsize(3cm,3cm,2cm);

viewportmargin=(2,2);


////// PLANES ///////
pen bg=gray(0.9)+opacity(0.2);
draw(surface((xmax,ymin,zmin)--(xmax,ymin,zmax)--(xmin,ymin,zmax)--(xmin,ymin,zmin)--cycle),bg);
draw(surface((xmin,ymax,zmin)--(xmin,ymax,zmax)--(xmin,ymin,zmax)--(xmin,ymin,zmin)--cycle),bg);
draw(surface((xmax,ymax,zmin)--(xmax,ymin,zmin)--(xmin,ymin,zmin)--(xmin,ymax,zmin)--cycle),bg);


xaxis3(Label("$x$",MidPoint,align=Y-Z),Bounds(Both,Min),InTicks(Step=1),p=black);
yaxis3(Label("$y$",MidPoint,align=X-Z),Bounds(Both,Min),InTicks(Step=.5),p=black);
zaxis3(Label("$z$",MidPoint,align=X-Y),Bounds(Both,Min),InTicks(Step=2),p=black);

for(real i;i<6.28;i=i+0.05) {
  currentprojection=perspective(camera=(2*cos(i),2*sin(i),2.5));    
  A.add();
  save();
}

A.movie(loops=3,delay=50);

Edit I followed Harish Kumar's suggestion and added a bounding box; it's better but still far from perfect.

Code (only the end changes):

for(real i;i<6.28;i=i+.1) {
  currentprojection=perspective(camera=(2*cos(i),2*sin(i),2.5));
  picture pic;
  add(pic,bbox(20mm));  
  A.add(pic);
  save();
}

Answer 1

It is better to insert a sphere, its projection does not depend on the camera (in this case). Please find the code

size(10cm,10cm);
import graph3;
import grid3;
//import animation;
import animate;

settings.render=1;
animation A;
A.global=false;

real xmin=-2, xmax=2;
real ymin=-2, ymax=1.5;
real zmin=-2.5, zmax=2.5;

limits((xmin,ymin,zmin),(xmax,ymax,zmax));

unitsize(3cm,3cm,2cm);

viewportmargin=(2,2);


////// PLANES ///////
pen bg=gray(0.9)+opacity(0.2);
draw(surface((xmax,ymin,zmin)--(xmax,ymin,zmax)--(xmin,ymin,zmax)--(xmin,ymin,zmin)--cycle),bg);
draw(surface((xmin,ymax,zmin)--(xmin,ymax,zmax)--(xmin,ymin,zmax)--(xmin,ymin,zmin)--cycle),bg);
draw(surface((xmax,ymax,zmin)--(xmax,ymin,zmin)--(xmin,ymin,zmin)--(xmin,ymax,zmin)--cycle),bg);

xaxis3(Label("$x$",MidPoint,align=Y-Z),Bounds(Both,Min),InTicks(Step=1),p=black);
yaxis3(Label("$y$",MidPoint,align=X-Z),Bounds(Both,Min),InTicks(Step=.5),p=black);
zaxis3(Label("$z$",MidPoint,align=X-Y),Bounds(Both,Min),InTicks(Step=2),p=black);
draw(scale(4,4,5)*unitsphere,invisible);

for(real i;i<6.28;i=i+0.05) {
  currentprojection=perspective(camera=(2*cos(i),2*sin(i),2.5));
  A.add();
  save();
}

A.movie(loops=3,delay=50);

You obtain this animation

O.G.