Grid navigation was also used, on a more limited basis, in the mid latitudes and again allowed a great circle track to be flown on a constant heading. This iteration is often referred to as "Greenwich Grid". Although any line of longitude can be used, the Prime Meridian (0 degrees) is most commonly used as the Reference (or Datum) Meridian. The aircraft gyro compass is aligned to this grid, either on the ground or during flight, and is corrected, as required, for change in longitude and gyro precession using celestial navigation sightings. In the polar regions, grid navigation is based on the use of a grid, most typically oriented parallel to a specified meridian of longitude, being overlaid on the appropriate Polar Stereographic projection navigational chart.
To overcome these obstacles, Grid Navigation was developed in the early 1940's and remained in use until late in the 20th century. Ground based navigation aids were few in number and widely spaced.Proximity of the magnetic poles - large and rapid changes in variation make magnetic compasses unreliable, even over relatively short distance.Convergence of the meridians of longitude - following a track that is anything but directly (true) North or South requires a constant change in true heading.Prior to the advent of Flight Management Systems (FMS) and of reliable area navigation systems such as the Global Positioning System (GPS), long range navigation in the polar regions, and within the large area of magnetic compass unreliability in Northern Canada, was difficult for three primary reasons:
A method of navigation using an grid overlay, appropriate to the map projection, instead of true or magnetic north for direction reference.
0 kommentar(er)
