Hi,
Thanks for your inquiry.
BNO055 heading is aligned to its +y axis. This means that when BNO055 +y axis is pointing to north, the heading angle is 0 degree. Please refer to BNO055 quick start guide app note at https://www.bosch-sensortec.com/media/boschsensortec/downloads/application_notes_1/bst-bno055-an007.pdf.
In BNO055 datasheet, at P1 orientation BNO055 x/y/z axes are aligned with product body X/Y/Z axes and with the same sign direction. Therefore, the heading 0 degree is when product body +Y axis (or BNO055 +y axis) is pointing to north. If for example BNO055 +y axis is mapped to product body -X, then when -X is pointing to north BNO055 heading output will be 0 degree.
Please see the attached "BNO055 axis remapping v2.pdf" for more info.
Thanks.
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