(These setting are enabled through the application preferences.)
Automatic time step.
When the override time step setting is disabled, which is encouraged, the solver uses a sophisticated method of automatically choosing an appropriate isochrone time interval, based on a number of factors.
Without going into great detail, the solver starts with an initial time interval of 20 minutes, or smaller, depending on how close to land you are. As the algorithm progresses, if the solver is encountering a lot of land intersections, it may choose to keep the time increment small. If the solver finds itself sailing in open waters then it starts to slowly increase the time step.
Generally, the maximum isochrone interval the solver chooses is 2 hours.
As the solver sees that it is starting to approach the target point, it will start reducing its time step. This has the effect of generating additional isochrone points, which generate more accurate arrival information.
Override automatic time step.
If you have a preference for generating all the isochrones at a single, fixed, uniform time interval then you can enable this setting and specify the interval.
One situation where you may want to set a fixed, small time increment, is if you are comparing the results of the LuckGrib WR solver to another system. Although, be aware that the results generated by LuckGrib may not be as good when using a fixed time interval. The automatic time increment method can produce superior results compared to a fixed time interval.
When comparing results between WR systems, you will likely want to do the comparison in LuckGrib, importing the other systems results via GPX files. LuckGrib has features which make doing the comparison easier than when doing it in other apps.
Open ocean time step example.
In this example open ocean passage, there are three paths generated, each with a different time step, and they are all essentially all the same. The time duration of the paths are, from left to right: 8 days 8.6 hours, 8 days 8.8 hours, 8 days 8.8 hours.
The largest difference between these three examples is the amount of time taken to compute the solution. On a 2017 13” Macbook Pro, the average of three runs for these examples is: 0.588 sec, 0.890 sec and 2.95 sec. (If you have experiences with a different weather routing system, how does its performance compare for these examples?)
Using the automatic time step is highly recommended.