Definition On Returned Fields for "PositionHistory"

We are using request /rest/ofscCore/v1/resources/{resourceId}/positionHistory and getting the below information returned:

These are all of the fields coming back:

"positionHistory[].acc"

"positionHistory[].alt"

"positionHistory[].dir"

"positionHistory[].i"

"positionHistory[].lat"

"positionHistory[].lng"

"positionHistory[].s"

"positionHistory[].spd"

"positionHistory[].time"

We are needing information on a definition for each of these fields and how they get populated. We were able to identify some of the fields, but we are still unable to identify what "s" and "i" stand for and what type of data would be pulled. Is anyone familiar with these 2 fields?