9.4. Merging procedure
The merging procedure as developed in the Access prototype tool for the sample data set is described in “AERO2K Merging tool” written by Nicu Stancioi (2002), (Appendix).
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The Great Circle (GC) is the shortest line that passes through two points on a sphere’s surface. The Great Circle trajectory generator function is to draw a Great Circle line between two points. A Great Circle Module was developed in ArcView 8.2 such as it could also be directly included into Access. It was used in two cases:
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For calculating the position of an aircraft passing midnight.
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In absence of data on the trajectory at the exception of the airport of departure and the airport of arrival i.e. schedule data extracted from Back Aviation database.
The position of an aircraft passing midnight was calculated using the function GreatCircleDistance and GreatCirclePoint. The function GreatCircleDistance is used to calculate the Great Circle distance between two points e.g. distance between start point and end point. The formula is:
GreatCircleDistance = (2 * Asn(Sqr((Sin((dLat1 -dLat2) / 2)) ^ 2 + Cos(dLat1) * Cos(dLat2) * (Sin((dLon1 -dLon2) / 2)) ^ 2)))
With Asn(x) = 2* Atn(X /(1 + Sqr(1-X ^ 2)))
GreatCircleDistance To get distance in nm divide by π and multiply by 180 then by 60 (1nm = 1 minute on Great Circle)
DLat1 Latitude in radians
dLat2 Latitude in radians
dLon1 Longitude in radians
dLon2 Longitude in radians
Asn Arcsinus
Sin Sinus
Cos Cosinus
Sqr Square
The function GreatCirclePoint allows to determine the latitude/longitude coordinates of a point along a Great Circle trajectory given a distance dDist. The purpose of this function is to interpolate a point when a leg starts before midnight and ends after midnight. The point is interpolated by calculating the distance between the start point and the end point then estimating the distance traveled at midnight proportionally to travel time (assuming a constant speed and a Great Circle trajectory).
d_midnight = d_total * (t_midnight -t_start) / (t_end -t_start)
d_midnight Distance at midnight
d_total Total distance
t_midnight Time at midnight
t_start Time at starting point
t_end Time at end point
In absence of information on the trajectory, using the Great Circle trajectory generator, eight points were created along the flight from the airport of departure to the airport of arrival. No altitude was assigned to the points. The time was calculated in a proportional manner.
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Implementation of AERO2K flight movement tool into an Oracle database.
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中國航空網(wǎng) www.k6050.com
航空翻譯 www.aviation.cn
本文鏈接地址：AERO2K Flight Movement Inventory Project Report(19)
