Expedition Navigation Software 
1 of 1- gillo
- Member
Offline - From: Italy
- Registered: 3/24/2017
- Posts: 3
Grid Based algorithm
Reading an article by werkstuk-korving I have started to question myself a bit more about the difference between Grid based and Isochronal algorithm. I have 2 questions:
1) The grid based method allows you to calculate the great circle route because it's using the formula to calculate the spheric distance between 2 points of the grid? while with the isochrone there is no such a calculation?
2) To calculate the "time sensitivity", do you need to do it with isochrone and inverse isochrone or there is a way to do it also with a grid based algorithm?
Thank you very much
- Nick
- Moderator
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- Registered: 9/16/2015
- Posts: 2,740
Re: Grid Based algorithm
The grid algorithm optimises based on a predefined grid of points to sail between. For the GC option, the grid is just one point wide. It just isn't implemented for the isochronal one as it would end up doing much the same thing.
The sensitivity works for both algorithms. It can run into issues for either if the routing solution is very non-linear.
- jko9369
- Expert
Offline
- From: Southern California
- Registered: 2/28/2017
- Posts: 25
Re: Grid Based algorithm
I have had great success with Expedition for longer offshore racing and routing, but have been running into a problem when trying to plan routing for an around the islands race. I have always used isochronal and "sail to mark", but for the around the islands races it doesn't always make sense to 'sail to' a mark, so I changed to "leave to......" and got the isochronal error, so I changed to Grid based and now every time I optimize, expedition crashes. I've tried changing the marks back and am successful in running routings back in isochronal. Any idea of what I might be doing wrong?
Thanks very much,
Jason
- Nick
- Moderator
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- Registered: 9/16/2015
- Posts: 2,740
Re: Grid Based algorithm
The generic answer for crashes is to turn off Avoid C-Map land and if that doesn't help, try the Expedition System restore in case something unknown has got messed up. If it still occurs, mail me the grib file(s), polar and marks.dat course file.