Position Referencing

Ground Position;

• This is the position on the ground directly beneath the aircraft.

Dead Reckoning (DR) Position;

• A DR position is the assumed ground position of an aircraft based on calculations from a previously known position and by applying the direction and speed of travel in the intervening period since that position.
• The correct term is deduced reckoning since the current position of the aircraft is deduced from previous knowledge.

Fix;

• A fix is a position derived from measuring external reference points visually such as the use of intersecting visual position lines.
• Two or more objects of known position are sighted, and position lines are recorded.
• The intersection of these lines is then the current position of the aircraft.
• The most accurate fixes occur when the position lines are at right angles to each other; it is advisable to aim at an intersection of nothing less than 45°.
• Fixes are a necessary part of navigation by dead reckoning because dead reckoning relies on estimates of speed and course, and the fix confirms an actual position during a journey. 

Position Line;

• A position line is defined as a line along which an aircraft is known to be at a particular time.
• A position line is not as specific as a fix because it will only indicate that the aircraft is somewhere along the line.
• It will not show where the aircraft actually is on the line.