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GPS internals: Difference between revisions
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;turn-rate-deg-sec | ;turn-rate-deg-sec | ||
: turn rate in degrees per second. Default value is 3.0, meaning a 180 degree turn takes one minute, which corresponds to a standard rate turn. This value is needed to compute turn anticipation correctly. | : turn rate in degrees per second. Default value is 3.0, meaning a 180 degree turn takes one minute, which corresponds to a standard rate turn. This value is needed to compute turn anticipation correctly. | ||
==Positional Source== | |||
The GPS code is entirely agnostic to how the primary position is obtained; hence calling the code a GPS is inaccurate, but convenient. 'Navigation computer' is a better name. In simple GPS mode, the position value is read directly from the <tt>/position</tt> properties, i.e the actual simulation position of the aircraft. | |||
In realistic mode, GPS position is calculated using an error filter that approximates the errors observed in real GPS receiver equipment. Config properties allow the simulation of selective availability (SA) and various augmentation systems such as WAAS and D-GPS to increase or decrease precision. | |||
In [[INS]] mode, position is supplied by a simulated inertial reference platform, which integrates acceleration values over time to compute velocity and hence position change. As in real life, the INS system will accumulate errors (drift) over time due to numerical and technical limits. Drift rate and other parameters can be configured to control simulated INS accuracy. | |||
In combined modes, position is calculated using multiple methods above. For example, GPS may be used to establish baseline position, and reset drift in an INS platform. Another possibility is to use INS for baseline position, and then use radio triangulation to correct for drift - this is the behaviour of the air navigation computers in the Boeing 757 and 767, for example. | |||