Hello Manuel,
The function pointCloud takes 3-D coordinate points as input argument. However, the variable 'a' here in the screenshot seems to be an 'sensor_msgs/PointCloud2' message struct. To return a point cloud, you would have to first use rosReadXYZ to extract the 3-D coordinate points and use it as the input to the pointCloud function.
In this case, the following code shall return the point cloud from a:
>> pts = rosReadXYZ(a);
>> ptCloud = pointCloud(pts);
Hope this helps,
Josh
