MATLAB: 3D-Animation plot with the hgtransform command

3d plotsanimationgraphicsmakehgtformMATLABtransform

I continue to think of the possibilities for the 3d-animation (moving point along a curve). I have written the following code to try it using the hgtransform command but I do not understand why does not work.
t = 0:pi/50:10*pi;
      x = sin(t);
      y = cos(t);
      z = t;
      ah = axes;
      set(ah,'XLim',[min(x) max(x)],'YLim',[min(y) max(y)],...
          'ZLim',[min(z) max(z)]);
      plot3(x,y,z,'Color','red');
      hold on;
      view(3);
      hpoint = line('XData',x(1),'YData',y(1),'ZData',z(1),'Color','black','Marker',...
          'o','MarkerSize',10,'MarkerFaceColor','black');
      ht = hgtransform('parent',ah);
      set(hpoint,'Parent',ht);
        for i=2:length(x)
            tx = x(i)-x(i-1);
            ty = y(i)-y(i-1);
            tz = z(i)-z(i-1);
            trans = makehgtform('translate',[tx ty tz]),      
            set(ht,'Matrix',trans);
            pause(0.01);
        end

Best Answer

I think the main reason why this doesn't do what you expect is this part right here:
tx = x(i)-x(i-1);
ty = y(i)-y(i-1);
tz = z(i)-z(i-1);
trans = makehgtform('translate',[tx ty tz]);
I think what you had indented was that at each iteration of the for-loop, you would translate the point from where it was at the last iteration to the next point. However, hgtransform doesn't work like that. The transformation don't accumulate. Once you set the transform's Matrix, that's it -- that's the transform. It doesn't matter what the Matrix used to be. (I think the documentation talks about that somewhere, but I can't seem to find it at the moment.)
So I think what you should do instead is first place the point at (0,0,0). On the first iteration, translate it to the first datapoint, on the next iteration translate to the second, etc. Like so:
t = 0:pi/50:10*pi;
x = sin(t);
y = cos(t);
z = t;
ah = axes;
set(ah,'XLim',[min(x) max(x)],'YLim',[min(y) max(y)],...
    'ZLim',[min(z) max(z)]);
plot3(x,y,z,'Color','red');
hold on;
view(3);
hpoint = line('XData', 0,'YData', 0,'ZData', 0,'Color','black','Marker',...
    'o','MarkerSize',10,'MarkerFaceColor','black');
ht = hgtransform('parent',ah);
set(hpoint,'Parent',ht);
for i=2:length(x)
    tx = x(i);
    ty = y(i);
    tz = z(i);
    trans = makehgtform('translate',[tx ty tz]);
    set(ht,'Matrix',trans);
    pause(0.01);
end
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