PCLVisualizer point cloud ID

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Hi,

first the code, than the question:

while (!viewer.wasStopped()) {
[...get coordinates...]
if (counter = true) {
    viewer.removePointCloud("1");
    viewer.addPointCloud(point_cloud, "2");
    counter = false;
}else {
    viewer.removePointCloud("2");
    viewer.addPointCloud(point_cloud, "1");
    counter = 1;
}
viewer.spinOnce();

Here the question: If I run this programm, I get "[addPointCloud] A PointCloud with id <2> already exists! Please choose a different id and retry". So my question is, if there is any possibility to free the old point cloud ID and write a new point cloud to the previous, now free, ID?

Thanks for the help.