I am currently writing a GUI in Qt (C++), and I've been on the lookout for something that will just let me open PCD images (point cloud), along with the ability to drag the image around.
I've looked through Blender, and MeshLab APIs (the latter defied my understanding), and lately PCLVisualizer to no luck.
Any input on the simplest way to go about this would be greatly appreciated.
Since you are writing your GUI in Qt, you might want to use a Qt widget developed to display 3D point clouds to use with the PCL library. It was written by Walter Lucetti and was available on his company website Rekno.it.
Unfortunately, the code is no longer available there. A quick web search pointed me to this github repository, which still holds a copy of the widget code. The relevant class is CPCLOpenglWidget. You can also find a complete example of PCL+QT+Kinect integration for real time point clouds visualization.