Editing Dynamic positioning (section)

===Other sensors===
Besides position and heading, other variables are fed into the DP system through [[sensor]]s:
*'''[[Inertial measurement unit|Motion reference units, vertical reference units or vertical reference sensors]], VRUs or MRUs or VRSs''', determine the ship's roll, pitch and heave.
*'''[[Anemometer|Wind sensors]]''' are fed into the DP system [[Feed forward (control)|feedforward]], so the system can anticipate wind gusts before the ship is blown off position.
*'''[[Draft (nautical)|Draught]] sensors''', since a change of draught influences the effect of wind and [[Ocean current|current]] on the hull.
*Other sensors depend on the kind of ship. A pipelay ship may measure the force needed to pull on the pipe, large crane vessels will have sensors to determine the cranes position, as this changes the wind model, enabling the calculation of a more accurate model (see Control systems).
*Some external forces are not directly measured. In these cases, the offset force is deduced over a period of time, allowing an average value of compensating thrust to be applied. All forces not attributable to direct measurement are labeled "current", as this is what they are assumed to be, but in reality this is a combination of current, waves, swell, and any errors in the system. As is traditional in the maritime industry, DP "current" is always recorded in the direction that it is flowing towards.