# WorldSense is a technology that provides positional tracking to [Daydream
Standalone](https://developers.google.com/vr/discover/daydream-standalone) headsets. WorldSense provides this
tracking on top of Daydream's rotational tracking, enabling
[6DoF](https://developers.google.com/vr/discover/degrees-of-freedom) capabilities.

WorldSense also provides an estimate of the last known position of the ground.

## Operating conditions

WorldSense uses advanced computer vision technology powered by dual fisheye
cameras to precisely track the user's head position. It does this by combining
feature points (visually distinct points in the environment) with inertial
measurements from the headset's IMU to estimate the user's position.

WorldSense is designed to work in both dim and bright lighting, as well as both
indoors and outdoors. As a rule of thumb, if the conditions are good enough for
you to read a book, they're good enough for WorldSense to track accurately.

WorldSense can also work reliably even if one or both cameras are partially occluded.

WorldSense relies on feature points and textures in the environment to track. It
can't track if you're looking at blank walls or other surfaces that lack
sufficient texture detail.

## Recovery

When conditions are insufficient for WorldSense to track properly, it automatically
falls back to [3DoF tracking](https://developers.google.com/vr/discover/degrees-of-freedom). This might happen
when there aren't enough feature points around, the lighting conditions are too dark,
or the cameras are completely occluded.

If the conditions improve, WorldSense is able to completely recover and 'remember'
where you are.

## Neck Model

WorldSense uses an integrated
[neck model](https://developers.google.com/vr/distribute/daydream/design-requirements#UX-D8) -
developers do not need to implement their own.

## Safety fog

Daydream Standalone automatically enables a safety fog to restrict tracking and
keep the user in a smaller space. All end users will have the safety fog turned
on. You can turn off the safety fog in developer mode for development purposes.

## Coordinate systems

Worldsense uses a head-centric coordinate system. This makes it easy to port from
[3.3 to 6.3](https://developers.google.com/vr/discover/degrees-of-freedom) as it's the same coordinate system
as in 3.3. When we recenter, we reset the origin. WorldSense also recenters each time
the user puts the headset back on.