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How to extract xyz coordinates from a 3D point cloud in MATLAB

I am using Kinect for Windows to import 3D images into MATLAB. I want to find the 3D coordinates of objects in a 3D scene.

One easy way to do this is to use the clickA3DPoint

function I found here and then click on the point I want to know - constraints.

The task clickA3DPoint

expects arguments in a matrix 3 by N

, which is coordinates x

y

and z

patterns N

. When I use Kinect to get a point cloud with depthToPointCloud

, it returns a matrix 480 * 640 * 3

.

How can I extract the x, y and z coordinates from this matrix so that I can plot it using clickA3DPoint

? (or scatter3

?)

My attempt:

depthDevice = imaq.VideoDevice('kinect',2)  %this is the kinect depth sensor

depthImage = step(depthDevice);  %this takes a depth image. (A 480 * 640 uint16 array)

xyzPoints = depthToPointCloud(depthImage,depthDevice); %convert the depth image to a point cloud

clickA3DPoint(reshape(xyzPoints,[3,307200])) %I'm guessing each of the 480 * 640 points (307200 points) has an x,y and z coordinate, so this concates the coordinates of all these points.

But this just draws points along a diagonal line in 3D space. How do I actually extract the x, y and z coordinates from a point cloud in Matlab?

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2 answers


You can use a function pcshow

to plot your points and it will take an M-by-N-by-3 array directly. You can then turn on data tips and click on the points on the graph to see their coordinates.

If you still want to create a 3-by-N matrix, then the easiest way to do it:



x = xyzPoints(:,:,1);
y = xyzPoints(:,:,2);
z = zyzPoints(:,:,3);
points3D = [x(:)'; y(:)', z(:)'];
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you can use the Location property for pointCloud to get x, y, z. eg:



moving = movingReg.Location;%movingReg is a pointCloud
scatter(moving(:,1),moving(:,2));
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