Container versus message
An MCAP file may contain many topics and schemas. For point-cloud viewing, the important question is whether a channel contains ROS 2 sensor_msgs/msg/PointCloud2 data the viewer can decode.
ROS 2 recording viewer
ROS 2 MCAP Viewer — Inspect PointCloud2 Recordings in Your Browser
MCAP is a container for timestamped message streams, not one sensor format. WolkeViz opens supported indexed ROS 2 MCAP recordings locally, lets you select a `sensor_msgs/msg/PointCloud2` topic, and provides timeline inspection, measurements, clipping, and PCD frame export without ROS 2, an upload, or an account.
At a glance
What to know before opening the file
Frame-aware inspection
Choose a point-cloud topic, move through the recording timeline, inspect frame rate and fields, and use persistence or accumulation when those views help interpret motion.
Selective PCD export
Export the current frame, every Nth frame, an inclusive range, or an approximately fixed number of frames distributed across a range. Multiple frames download as binary PCD files in a ZIP with a provenance manifest.
Practical workflow
Inspect a PointCloud2 recording frame by frame
- Open the MCAP file in WolkeViz and review the available PointCloud2 topics.
- Select a topic, then fit the first frame and check its reported fields, point count, and bounds.
- Use the timeline to inspect the sequence; compare current-frame, persistence, or accumulation views when appropriate.
- Choose a single frame, every n frames, an inclusive frame range, or a requested count of evenly spaced frames for export.
Technical notes
What a PointCloud2 viewer must understand
ROS 2 PointCloud2 messages describe a rectangular or unorganized cloud using width, height, point_step, row_step, endianness, and a list of PointField definitions. The field definitions identify the byte offset, datatype, and count for coordinates and optional attributes such as intensity or colour.
WolkeViz uses MCAP indexes to locate selected messages without reading the entire recording into memory. Current MCAP support is for ROS 2 PointCloud2 streams in uncompressed or Zstd-compressed chunks; ROS 1 bags, SQLite .db3 rosbag2 storage, camera topics, and arbitrary custom schemas are outside this viewer workflow.
Playback and accumulation do not apply TF, odometry, SLAM, pose alignment, or motion compensation. A moving sensor can therefore produce smeared accumulated views. Export preserves source coordinates and records available provenance, but the final multi-frame ZIP must fit in browser memory.
See it in use
Watch the workflow.
See WolkeViz open and inspect a ROS 2 MCAP point-cloud recording in the browser.
Questions and answers
Common questions
Can I open any MCAP file in a point-cloud viewer?
No. MCAP is a container. WolkeViz is intended for supported ROS 2 recordings containing sensor_msgs/msg/PointCloud2 data; other schemas such as images or custom messages need tools that understand those message definitions.
Can I extract multiple PointCloud2 frames from MCAP?
Yes. WolkeViz supports a single frame, every n frames, a selected start/end range, or a specified number of evenly spaced frames from a range.
Do I need ROS 2 installed to inspect a supported recording?
No. A browser workflow can be useful for first inspection of a supported local recording before setting up a complete ROS 2 environment or conversion pipeline.
Keep exploring