Hello! Since the names are pretty cryptic, I wanted to ask if anyone has a detailed list of explanations of what all the data fields mean. So far, I only understand a few such as d->qpos, qvel, ctrl, but if there is more information on them, that would be great.
There are comments in mjdata.h that provide a bit more information beyond the field names. The inputs and outputs and the top-level functions are described in the documentation. The other fields are internal variables, which would normally be hidden from the user but I decided to expose them in case someone finds them useful. However documenting every internal variable at the level of details as documenting the inputs and outputs would be too much work. That being said, if there is a specific thing you are trying to do and you do not understand what the relevant field of mjData means, please post a question here.