The Calculation Options tool displays computations in STK's Aviator capability. You can adjust some of the parameters that influence Aviator's computational performance. The information and parameters in the tool describe and affect the procedure or phase that is currently selected in the Mission List.
Adjusting calculation options to improve compute speed is not a straightforward task. As discussed below, change options towards faster propagation can in some instances cause calculations to run slower. For those who wish to optimize calculation, it is recommended to make a change, click apply, and note how “X Real Time Factor” changes. If this number increases, calculation performance has improved.
Overall Calculation Stats
The Overall Calculation Stats group displays the general calculation time information.
| Field | Description |
|---|---|
| Total Calculate Time | The total amount of time that it took to calculate the selected phase or procedure |
| Total Duration | The total duration of the selected phase or procedure within the scenario |
| X Real Time Factor | A real-time factor that represents the ratio between the calculation time and the duration. |
Duration Goal Seeking Stats
If you have defined two fixed times for the selected phase or procedure, the Duration Goal Seeking Stats group displays information about the computation required to satisfy those time requirements.
| Field | Description |
|---|---|
| Calculate Time | The amount of time that it took to calculate a solution to the time requirements. |
| Fraction of Total | The percentage of the total calculation time that was consumed by calculating the solution to the time requirements. |
| Number of Iterations | The number of iterations of the time computations that were performed while solving for the time requirements. |
| Number of Bad Steps | The number of bad iteration steps (in which the computed value was a worse solution than the previous step) that were generated while solving for the time requirements. |
Converge Procedure / Site Time Stats
If the selected phase or procedure has asynchronous times and locations, and you have required Aviator to converge them, then the Converge Procedure / Site Time Stats group displays information about the computations required to achieve those convergences.
| Field | Description |
|---|---|
| Calculate Time | The amount of time that it took to calculate a solution to the procedure convergence. |
| Fraction of Total |
The percentage of the total calculation time that was consumed by calculating the solution to the procedure convergence. |
| Number of Iterations |
The number of iterations of the time computations that were performed while solving for the procedure convergence. |
| Number of Bad Steps |
The number of bad iteration steps (in which the computed value was a worse solution than the previous step) that were generated while solving for the procedure convergence. |
Max Rel Motion Factor
The Max Rel Motion Factor is an abstraction of the maximum motion allowed between sampling points along the aircraft's route. A low factor (less than 1) will increase the accuracy of the route and the calculation time by requiring more frequent sampling, while a high factor (greater than 1) will decrease the accuracy of the route and the calculation time by allowing more motion to occur between sampling. However, a higher factor will increase the chance for errors, which may require re-calculation and increase overall calculation time. Users should be prepared to experiment to find the optimal setting for speed.
State Cache Time Interval
Aviator stores state information at intervals along the aircraft's route so that recalculating a route to reflect mission changes does not require it to reintegrate from the beginning. The State Cache Time Interval allows you to control the size of the cache used to store these intervals; a larger cache increases recalculation speed and the amount of memory consumed, while a smaller cache decreases recalculation speed and the amount of memory consumed. However, using a larger cache requires more calculation time spent saving states to the cache, which could eventually outweigh the benefit of faster calculation speed. As with Max Rel Motion factor, you should be prepared to experiment to find the optimal setting for their scenario. When using a fixed time step integrator such as RK4, the state cache time interval also serves as the step size.
Time Processing
The Time Processing property group allows you to control Aviator's performance when attempting to solve for duration goals or procedure convergence.
| Field | Description |
|---|---|
| Time Resolution / Accuracy | The tolerance permitted for the goal or convergence. |
| Maximum Iterations | The maximum number of iterations that Aviator will perform to solve for the goal or convergence. |
| Maximum Bad Steps | The maximum number of bad iteration steps (in which the computed value was a worse solution than the previous step) the Aviator will allow before ceasing computation; an error message will be displayed in the Message Viewer. |
Integrator Options
The Integrator Options property groups enables you to change the numerical integrator that Aviator uses to compute trajectory. The following integration methods are available for propagating the aircraft:
-
RK4 - Runge-Kutta 4th order without error control.
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RKF45 - Runge-Kutta-Fehlberg 4th order with 5th order error control.
Integrator Best Practices
One significant difference between the RK4 and RK45 integrators is the step size that they employ. The RK45 integrator varies the step size to limit the estimated error to the prescribed accuracy. The RK4 integrator uses a fixed state cache time step as the step size without error control.
In most cases, RK45 is recommended to balance speed and accuracy. RK45 optimizes step size based on estimate integration error and usually uses fewer steps to calculate a trajectory. RK4 usually requires a small time step to produce smooth, accurate results during manevuers, wasting computational steps when not maneuvering. RK4 can also increase time for data analysis due to extra STK data calls. You can observe X real-time factor to determine which integrator is best.
The Basic Maneuver procedure is heavily dependent on the numerical integrator and typically allows for more dynamic maneuvers than other procedures. For Basic Maneuver procedures that are appropriate to use with the RK4 integrator, the calculation speed can be up to 2.5x faster than the RK45 integrator. For all other procedures, you can expect an increase in speed of up to 1.2x faster than the RK45 integrator.