It needs a reference point in order to start measuring.
Absolute angle sensors.
For this a unique code pattern is assigned to each angle increment.
The number of code patterns available per revolution determines the resolution.
When you say incremental position sensor it implies a change in position.
Each code pattern forms a unique reference and is therefore an absolute position.
Absolute encoders generate information about position angle and rotation counts in type specific angle steps.
Common types of position sensors include.
A position sensor is a sensor that facilitates measurement of mechanical position.
The position sensing element is a permanent magnet.
Absolute versions of transmissive encoders incorporate multiple tracks light sources and sensors which completely define position within a revolution.
Absolute position sensors are very different from incremental sensors.
With mechanical gearing of one disc to second disc it is possible to define position over multiple revolutions.
A position sensor may indicate absolute position location or relative position displacement in terms of linear travel rotational angle or three dimensional space.