I have the same problem for two datasets and I rely on the CSV calibration file including the internal/external camera parameters for my workflow.
The first dataset is an outside-in capturing. I can convert Heading-Pitch-Roll to a rotation matrix following the workaround from Sasha with
heading = heading - 180
roll = roll - 180
and using YXZ order.
For the other dataset (inside-out camera array) I just have to change the order to ZYX to get the correct 3x3 matrix. Altering Heading-Pitch-Roll is not required there (in contrast to the first dataset).
For my workflow I need a reliable automated way to import the calibration file and convert the euler angles to a matrix. However if the conversion differs between datasets it’s impossible for me to find the correct conversion without manual checking.
Is there any update on this from the RealityCapture support? Maybe a little explanation how Heading-Pitch-Roll is generated. I’m getting out of ideas and it’s frustrating.