How can I convert PointCloud2 to PointCloud?

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Hi ! I have some problems when I run a "laser-perception.launch" of PR2. The errors are:

Client [/point_cloud_assembler] wants topic /tilt_scan_cloud_filtered to have datatype/md5sum [**sensor_msgs/PointCloud**/d8e9c3f5afbdd8a130fd1d2763945fca], but our version has [sensor_msgs/PointCloud2/1158d486dd51d683ce2f1be655c3c181]. Dropping connection

and so is the topic /tilt_scan_cloud. The topics' type is sensor_msgs/PointCloud2.

So I think the solution is that PointCloud2 should be converted to PointCloud. But I don't know how convert PointCloud2 to PointCloud in a launch file. thank you so much.