In the AI domain, if an Airspace border has two consecutive points at the same geographical latitude, it is assumed that the line between the two points is “along the parallel”. This shall be encoded in AIXM/GML using “linear” GML elements in combination with a geodetic CRS, such as EPSG:4326. The linear interpolation in a 2D geodetic CRS between two points that have the same latitude corresponds to a parallel on the Earth’s surface. This is shown in the figure below:
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| The current GML 3.2.1 does not allow general “rhumbline” (constant angle with the meridians) interpolations to be specified directly (e.g. using a RhumbLine element or a “rhumbline” interpolation). However, linear interpolations in certain conformal projections do correspond to rhumblines on the ellipsoid Earth model. |
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