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The objective is to find a point that is at equal geodesic distance from the start P2 and end P4 points. This can be done with an algorithm that iteratively tries to find the point of which the distance to both P2 and P4 is the same and which is as close as possible to the original center. However, if the difference between the original distances P3-P2 and P3-P4 is higher than 1%, then the application shall raise an error message and abort the calculation. This rule was also specified in previous AIXM versions (4.5) and it did prevent the provision of geometrically inconsistent arc data.
The calculated point (P3') can then be used as the corrected center point. The corrected radius is the distance from the corrected center P3' to P1 (because of the algorithm applied, this distance is also the distance to P2). The start/end angles are the bearings from the corrected center P3' to P1/P2.
There might be situations where the centre P3 is an Aerodrome Reference Point (ARP) or a Navaid. In this situation, it might be more appropriate to re-calculate the points P2 and P4 in order to correctly close the surface. This could be problematic when P2 or P4 are also ends of arcs. The best solution depends on the intended use of the data, therefore this decision is left to application developers.
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