ReSim Log Format

The ReSim app is designed to work with any log format. This way, you can ensure that your simulation jobs produce the same types of logs that you might have from real-world data collection. This is often essential for tool or library re-use. In ReSim's open source library, however, we are working to provide a rich set of tools for computing and visualizing salient metrics. We further aim to continue producing tools to analyze and leverage data from both simulation and real-world logs in the open source library. As we cannot write such tools to work with any log format, we maintain our own ReSim Log Format. We want this format to be as simple and portable as possible so that converters from other common robotics log formats are as trivial as possible. To this end we define the format like so:

The ReSim Log Format is based on Foxglove's MCAP file format. Using this file format furnishes us with a pre-existing set of open source tools and libraries for reading, writing, and visualizing our logs. In particular, Foxglove Studio natively visualizes this format efficiently.

Those familiar with the MCAP format will be aware that this format can hold arbitrary serialized robotics data with ROS1, ROS2, JSON, Flatbuffers, and Protobuf recieving first-class support from Foxglove's open-source libraries. Therefore, we define a set of protobuf message schemas in open-core/resim/msg which our tools are designed to recognize and work with efficiently. This allows all of ReSim's metrics libraries to be leveraged for the small cost of writing log converters. For the ubiquitous ROS2 middleware log format (CDR), such converters are provided for the defined ReSim message types. With that said, we have deliberately chosen to promulgate our own log format rather than using ROS's so that our users are not forced to depend on this large software ecosystem if they would prefer not to. Simultaneously, our provided converters eliminate integration friction for ROS users.

A ReSim log therefore consists of an MCAP file containing ReSim messages for topics of interest. Other topics may be present and may have any schema/serialization. These topics will generally be ignored by ReSim tools, or copied unmodified by tools that input and output mcap files. There may be exceptions to this in the future.