Fix
Fix turns up in 2 fields: hydrography, aviation. Here is what it means to the people in each one.
Fix in hydrography
A measured position of the survey vessel at a recorded instant, and the act of determining it.
A determined position at a known time. Without satellite positioning, a survey boat takes fixes at set intervals by sextant angles or ranges, numbering each on the record so soundings between fixes can be plotted. Crews use the word for check fixes against known marks, the fixed versus float status of RTK, and log entries such as fix lost or fix regained.
"Take a check fix on the beacon before you start, the nav looked off yesterday."
Fix in aviation
A fix is a specific geographical position determined by visual reference or navigational instruments.
A fix is a known location in the sky or on the ground used to establish an aircraft's exact position. It is derived from intersecting radio navigational radials, GPS coordinates, or prominent terrain features. Pilots use fixes to navigate airways, report their position to air traffic control, and execute instrument approach procedures.
"ATC, we just crossed the initial approach fix and are descending to three thousand."