Site, drive, and pose
Instead of street addresses or latitude/longitude, rover locations are given as a combination of site, drive, and pose (or sometimes just site and drive, or even just site).
Site, drive, and pose define a location hierarchy. The science team (somewhat arbitrarily) declares a location as a new site. That resets the drive and pose values to zero, for example, site 4, drive 0, pose 0. When the drive system determines it's time for a new drive location within the current site, the drive is incremented and the pose is reset to 0. The values for site almost always increment by 1. Drive values rarely do.
| Site | The Site index defines which instance of the Site frame is relevant a particular rover motion counter (RMC). Whenever the Site frame is incremented, all the other RMC values are set to 0. Declaring a new Site frame thus resets all motions and creates a new local area in which to work. Unlike the other indices, there is no meaning to odd or even values. Also, unlike other indices, Sites start with 1 (the landing site), not 0. |
| Drive |
The Drive index (sometimes incorrectly called Position) increments whenever the rover drives or otherwise moves its wheels (e.g., trenching or steering). The value is odd while the wheels are actually moving, and even while they are not. Incrementing Drive sets all the subsequent indices (i.e., all except Site) to 0. Exception: if a mechanism index is odd, indicating it is moving during the drive, then that index is not reset to 0. This should be an unusual case, however. The Drive index is the one of highest interest for most localization activities |
| Pose |
The Pose index indicates a change in the rover’s knowledge of its position or orientation, when it is not actually driving. Unlike the other indices, it does not indicate that anything actually moved; only that the pose knowledge has changed. This may be due to running visodom (visual odometry), doing a sun find, reading the IMUs (Inertial Measurement Units), or receiving an explicit ground command to update the pose knowledge. Note that the rover might actually have moved slightly, mostly in orientation, due to being pushed by the arm (e.g., during a drill preload). There is unfortunately no reliable way to distinguish this from an attitude update, although the arm index will change during arm movements. So, a pose change does not indicate arm-induced motion, but lack of an arm update does rule it out. |
Site/drive/pose locations are often shown in the Notebook without using the words drive and pose. For example, you might see Site 8 / 610 / 4 meaning site 8, drive 610, pose 4.
The ROVER_MOTION_COUNTER value in data product labels contains the site, drive, and pose information for a given product.
note
The science team sometimes refers to "site and position" rather than "site and drive". Yes, it can be confusing.