Plot not showing a line, only individual points(one at a time)?

When I graph my plot, I used the drawnow function and it would plot individual points, then move on to the next without saving the previous point or drawing a line. Any suggestions?

altmax=-inf;
days=10;
dy=-1;

while dy<=days

%--calculate & display current time (UTC)
    yr=2018;
    mnth=1;
    dy=dy+1;
    hr=0;
    min=0;
    sc=0;
    d=datetime(yr,mnth,dy,hr,min,sc);
    %d=datetime('now');

%--covert and display current time in julian days
    JD_TT=juliandate(d);

%--convert julian days to moon position
    CooType='q2000';
    [X,Y,Z]=moonpos(JD_TT,CooType);
    %plot3(X,Y,Z);

%--convert to LLA coordinates, in degrees
    alt=sqrt(X.^2+Y.^2+Z.^2);

      xplot=dy;
      yplot=alt;    
      plot(xplot,yplot,'-o');
      drawnow

end

Answer 1

[Geoff Hayes]

Evan - with each call to plot, you are creating a new plot graphics object. Since you are not calling hold on, then all previously drawn graphics objects will be removed. So you could add a hold on statement to fix this problem or, rather than creating dozens (or more?) plot graphics objects, just keep re-using the existing one.

 altmax=-inf;
 days=10;
 dy=-1;
 hPlot1 = plot(NaN,NaN); % create a plot graphics object with handle hPlot1
 while dy<=days
     % your code

     % when ready to plot the data... 
     xdata = get(hPlot1,'XData');
     ydata = get(hPlot1,'YData');
     set(hPlot1,'XData',[xdata dy],'YData',[ydata alt]);  
     drawnow;
 end

So when you have calculated dy and alt, we get the current set of XData and YData from the plot graphics object and then update it with the new data points. Try the above and see what happens!

[Evan Mossel]

AHA! Thank you very much!

[Evan Mossel]

What does NaN mean in this instance?

[Geoff Hayes]

NaN is just "not a number" (see NaN for details).