Hitesh P asked . 2022-01-11

3D point cloud

I am trying to get a 3D point cloud using the following code:

output_dir = 'C:\Users\Xyz\Desktop\Matlab';
%%set up webcam
 delete(imaqfind)
leftCam = imaq.VideoDevice('winvideo', 2, 'YUY2_640x480');
rightCam = imaq.VideoDevice('winvideo', 1, 'YUY2_640x480');
%%load stereo parameters if required
if ~exist('stereoParams', 'var')
    load stereocalibration.m;
end
ax = axes;
maxDepth = 5;
clear maxdepth;
while true
imageLeft = step(rightCam);
imageRight = step(leftCam);
[J1, J2] = rectifyStereoImages(imageLeft, imageRight, stereoParams);
disp = disparity(rgb2gray(J1), rgb2gray(J2), 'DisparityRange', [0, 112]);
pointCloud = reconstructScene(disp, stereoParams) ./1000;
z = pointCloud(:,:,3);
z(z<0) = NaN;
z(z>maxDepth) = NaN;
pointCloud(:,:,3) = z;
if ~ishandle(ax)
    break;
else
    showPointCloud(pointCloud, J1, 'VerticalAxis', 'Y', 'VerticalAxisDir', 'Down', 'Parent', ax);
    
    xlabel('X (m)');
    ylabel('Y (m)');
    zlabel('Z (m)');
    xlim(ax, [-.8, .8]);
    ylim(ax, [-.8, .8]);
    zlim([ax, maxDepth]);
    drawnow;
end
end
release(leftCam);
release(rightCam);

ERROR:

Error using matlab.graphics.axis.Axes/horzcat

Cannot convert double value 5 to a handle.

MATLAB R2015a

matlab , 3d plots , error

Expert Answer

Prashant Kumar answered . 2024-12-21 16:24:48

You need to learn to use the debugger. Or you need to learn to provide sufficient information, with the complete error message that arose, so what line failed. However, I will hazard a guess that what you did was make a syntax error.

You form the variable ax as:

ax = axes.

When you do that in MATLAB, for example...

plot(1:5)
>> ax = axes
ax = 
  Axes with properties:

             XLim: [0 1]
             YLim: [0 1]
           XScale: 'linear'
           YScale: 'linear'
    GridLineStyle: '-'
         Position: [0.1300 0.1100 0.7750 0.8150]
            Units: 'normalized'

  Show all properties

As you can see, the result is a handle to the axes in a figure.

Then later on, you did this:

xlim(ax, [-.8, .8]);
ylim(ax, [-.8, .8]);
zlim([ax, maxDepth]);

Do you see that in the calls to xlim and ylim, you used one form, yet when you called ylim, for some reason, you did something completely different?

In fact, inside the call to zlim, you tried to catenate the number 5 to a graphics handle?

maxDepth = 5;

Now, go back and READ THE ERROR MESSAGE YOU GOT. maxdepth is the number 5.

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