Fix (position)
Encyclopedia
In position fixing
navigation
, a position fix or simply a fix is a position derived from measuring external reference points.
The term is generally used with manual or visual techniques such as the use of intersecting visual or radio position line
s rather than the use of more automated and accurate electronic methods such as GPS. A visual fix can be made by using any sighting device with a bearing indicator. Two or more objects of known position are sighted, and the bearings recorded. Bearing lines are then plotted on a chart through the locations of the sighted items. The intersection of these lines is then the current position of the vessel.
Usually, a fix is where two position lines intersect. If three position lines can be obtained, the resulting "cocked hat", where the 3 lines do not intersect at the same point, but create a triangle where the vessel is inside, gives the navigator an indication of the accuracy in the three separate position lines.
The most accurate fixes occur when the position lines are at right angles to each other.
Fixes are a necessary part of navigation by dead reckoning
because dead reckoning relies on estimates of speed
, course
. The fix confirms the actual position during a journey. The fix itself can introduce inaccuracies if the reference point is not correctly identified or is inaccurately measured.
Position fixing
Position fixing is the branch of navigation concerned with the use of a variety of visual and electronic methods to determine the position of a ship, aircraft or person on the surface of the Earth.These techniques include:...
navigation
Navigation
Navigation is the process of monitoring and controlling the movement of a craft or vehicle from one place to another. It is also the term of art used for the specialized knowledge used by navigators to perform navigation tasks...
, a position fix or simply a fix is a position derived from measuring external reference points.
The term is generally used with manual or visual techniques such as the use of intersecting visual or radio position line
Position line
A position line is a line that can be identified both on a nautical chart or aeronautical chart and by observation out on the surface of the earth...
s rather than the use of more automated and accurate electronic methods such as GPS. A visual fix can be made by using any sighting device with a bearing indicator. Two or more objects of known position are sighted, and the bearings recorded. Bearing lines are then plotted on a chart through the locations of the sighted items. The intersection of these lines is then the current position of the vessel.
Usually, a fix is where two position lines intersect. If three position lines can be obtained, the resulting "cocked hat", where the 3 lines do not intersect at the same point, but create a triangle where the vessel is inside, gives the navigator an indication of the accuracy in the three separate position lines.
The most accurate fixes occur when the position lines are at right angles to each other.
Fixes are a necessary part of navigation by dead reckoning
Dead reckoning
In navigation, dead reckoning is the process of calculating one's current position by using a previously determined position, or fix, and advancing that position based upon known or estimated speeds over elapsed time, and course...
because dead reckoning relies on estimates of speed
Speed
In kinematics, the speed of an object is the magnitude of its velocity ; it is thus a scalar quantity. The average speed of an object in an interval of time is the distance traveled by the object divided by the duration of the interval; the instantaneous speed is the limit of the average speed as...
, course
Course (navigation)
In navigation, a vehicle's course is the angle that the intended path of the vehicle makes with a fixed reference object . Typically course is measured in degrees from 0° clockwise to 360° in compass convention . Course is customarily expressed in three digits, using preliminary zeros if needed,...
. The fix confirms the actual position during a journey. The fix itself can introduce inaccuracies if the reference point is not correctly identified or is inaccurately measured.