How to export pcd file？

[Forrest-Z]

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Environment (please complete the following information):

• CPU/GPU: [e.g., Core i9-9900K/RTX2080Ti]
• OS: [e.g. Ubuntu 20.04]
• ROS: [e.g., ROS1 noetic/ROS2 galactic]
• CUDA: [e.g., CUDA 11.6]
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