Saturday 8 December 2018

Airspaces - grouping by shape

In terms of GIS - airspace is a polygon with certain atributes. Polygon shape, as we know, is described by pairs of coordinates (lon, lat). Let's look at some description of airspace, which you can find i aeronautical publications:
Can you spot the problem with boundaries? Airspace shape (boundary) in aviation publications are often not given directly as pairs of longitude and latitude. Generally speaking boundaries are defined as geodesic lines between points (fixes, waypoints, nvaigation aids etc.), or  points deifned by bearing and distence against another point (navigation aid, airport reference pioint etc.). Boundary of airspace can also be: political boundary, road, railway, river, coastline or boundary of other airspace.

To deal with it effecitvely we can distinguish following types of airspace according to their shapes:

  • circle: defined by center and radius
  • circle: center defined by bearing (magentic or true) and distance against point with known longitude and latitude and radius
  • circle section ('pizza slice'): deifned by bearings (from - to) and distance against point
  • part of circle, defined by bearings (from – to) and two distances:
  • rectangle:
    • deifned by bearing, distance from - to against point (it defines 'center line'), and buffer:
      • symetrical buffer (the same of each side of 'central line'
      • non-symetrical (left and right buffer value are different)
    • deifned between points with known locations and buffer
  • defined by two arcs: one is clockwise, second one is anti-clockwise, with different arc center and different radius; start and  end point of each arc are the same and cna be defined as bearing and distance against center of one of arc
  • complex shape that can be obtained by combining various airspace shape described above

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