The supported point cloud formats are Autodesk® ReCap® .rcs and .rcp, which can be imported into a Visualize database and rendered, with automatic level-of-detail.
.ptx is not supported. If you need it, convert to .rcs first (ReCap and several third-party tools do this), or import the points as an unstructured point cloud — Visualize accepts point data directly, and an unstructured cloud can afterwards be converted to the .rcs-based form to get level-of-detail. See the PointCloud2Visualize and Rcs2Visualize examples.
