Add a simplified and commented TimeToPlane algorithm
#1253
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This change replaces the previous implementation of `TimeToPlane` with a new one that is simpler and more commented. It also fixes a bug in the handling of `LANDifference`: because `LANDifference` was subtracted as the very last step in the angle computations, a positive value could cause the output of `TimeToPlane` to be negative, leading to an immediate launch even when that was not correct. Also, there is now a special case for very low inclinations (<.01 degrees); since there's such a small difference between different launch times, the function now just returns 0. The old implementation always returned a launch point 90 degrees away when the inclination was exactly 0.
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I actually cleaned that one up months ago on a branch I never pulled due to other issues with it. I just rescued that in PR #1260, can you look at that and see if it works? Its a little more extensive than what you had, and I just use one of napier's analogies from spherical trig to solve the problem (which is why I kind of prefer that solution since its just using a prebaked spherical trig algorithm and doesn't require any exposition or proof). |
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replaced by #1260 |
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Oh neat, that's some cool math. |
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Yep, mathematicians already solved that one, I just needed to teach myself enough spherical trig to figure out which formula was simplest to apply. |
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This change replaces the previous implementation of
TimeToPlanewith a new one that is simpler and more commented.It also fixes a bug in the handling of
LANDifference: becauseLANDifferencewas subtracted as the very last step in the angle computations, a positive value could cause the output ofTimeToPlaneto be negative, leading to an immediate launch even when that was not correct.(I'm not sure
LANDifferenceis being set in the most useful way to begin with; it seems to always be better to leave it at 0 than use the value MJ fills in after a launch. But that's a separate discussion.)Also, there is now a special case for very low inclinations (<.01 degrees); since there's such a small difference between different launch times, the function now just returns 0. The old implementation always returned a launch point 90 degrees away when the inclination was exactly 0.