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7/29/2021 6:43 am  #1


Grid routes - avoid land

Hi - trying to resolve a Grid routing error in latest 4D version. Easy route avoiding land and with a small amount of land works fine, but a third route over more land results in the error. Isochronal is fine, weather covers the full period, avoid land is 'on' but ENC is irrelevant and 'off' (settings below), and I don't think the race notes are any issue.

Does Grid have a limit on the amount of land it can route around?

Thanks! 


 

7/29/2021 8:24 am  #2


Re: Grid routes - avoid land

Hmmm -- I'll try to give it a play in the next day or so but everything you are doing looks right to me.

I know Nick has been making improvements in the routing code in recent releases - this could be a new bug.

A test you can do to see if it is just your wind grib being on the edge of having enough data (in the time sense) - you can check extend wind in time and see if it works --- if not I would suspect you found a bug.

I've run the fast net route in the past with both algorithms and 3 points using avoid land.

 

7/29/2021 8:41 am  #3


Re: Grid routes - avoid land

Thanks Sparky, much appreciated.

Confirming gribs are PW PWG/PWE for 5 days downloaded this morning (and this short route was run from today so should be well within the grib timings). Confirming also that the error also occurs with extend wind in time.

No issues with similar routes slightly adjusted. Tried a few more times and just moving Mark 2 a few degrees east or west results in differing successful or failed grid route.

Running latest release - 11.10.16. Thanks!

     Thread Starter
 

7/29/2021 1:04 pm  #4


Re: Grid routes - avoid land

You can look at the Simple world chart to see what its land to avoid looks like - this is the default option. There is also a higher resolution simple world chart that can be used, but is a little slower.

I suspect the UM model might be best for Fastnet this year and Arome and WRF will come into play closer to the race.

Last edited by Nick (7/29/2021 1:12 pm)

 

7/29/2021 2:11 pm  #5


Re: Grid routes - avoid land

Thanks Nick - afraid it's still an error on GFS on Simple world chart (with and without optimise first leg only to ensure within grib time period). Screenshot below.

Grid works fine on same route and gribs on desktop running 11.10.13.

Should I reinstall / rebuild registry?



Also a minor flag but PW in Exp on 11.10.13 shows GFS / PWE / PWG for download, but 11.10.16 shows only PWE / PWG... I am sideloading via PW Offshore App for now.

Last edited by eb12345 (7/29/2021 2:19 pm)

     Thread Starter
 

7/29/2021 7:21 pm  #6


Re: Grid routes - avoid land

Hello,

You could email me the route and race notes and I could test. Am on vacation this week, so replies are slower than normal. Putting 3 marks roughly as you have done works for me though.

For a route like that, I would normally add a mark outside the Solent though and make sure you have Fastnet Rock to be set to sail to rather than leave to port.

The PW GFS option was deleted as the data encoding has too many errors and will not mix nicely with other data. I never use it, so hadn't tested it until someone asked about it a few weeks ago. GFS from Expedition, Saildocs and Squid are all better options anyway. The other PW options are still there, but will never be nearly as good as WRF, Arome etc.

The Iscochronal option should yield a slightly better solution too. We have been using the TG (tack/gybe) routing 
button a lot with it recently.

Btw, the paths option can show you how far and where Exp has explored and managed to get to.

Last edited by Nick (7/29/2021 8:52 pm)

 

7/30/2021 12:33 am  #7


Re: Grid routes - avoid land

I'll bet you are getting an error in the last run (with the first mark off Cowes). Exp may struggle to lay down points getting out of the Solent without hitting land.

I'll also bet that the initial errors could be overcome with an adjustment to your routing resolution (using custom). As Nick states, drawing paths goes a long way to see where the routing has got to before an error.


:::Campbell Field::::::www.fieldyachting.com:::
 

7/30/2021 9:19 pm  #8


Re: Grid routes - avoid land

Yes, seeing EB's data, the grid routing couldn’t get out of the Solent with default settings.
 
The PW model and data are low resolution and the grid routing works on a grid that is based on the data resolution which is ½ degree in this case. For comparison, GFS, UM, ICON, GDPS Arpege, WRF etc are available at 0.08 – 0.15 degrees.
 
So with the start point on the RYS line behind the Isle of Wight and the next set of points outside the Solent, the router can’t see a path that doesn’t cross land.
 
As Campbell says, you can set a custom resolution that would help/resolve this.
 
I almost always have Expedition set to show the paths. It can be very helpful in showing what the solution means and in this case immediately shows what the issue was.
 
The grid routing was originally designed for routing studies where we wanted to compare the same thing many times and it is faster.
 
Generally the isochronal routing will be a little better especially in light airs and with currents, but is slower.

Similarly, the high resolution avoid land option is better, but noticeably slower.

I think most people will/should generally use the iso routing and occasionally have the grid routing for a comparison.
 
One thing we have been finding very useful recently is to use the TG (Tack/gybe) option with isochronal routing.
 

 

8/06/2021 10:57 am  #9


Re: Grid routes - avoid land

Thanks very much Nick and Campbell, very much appreciated and that's done the trick!

Could I please sense-check the output of an isochronal route run just now? The TWA seems too low at certain points - is this just short-tacking and not showing each individual tack?

Tack and gybe at steps seems to work fine (e.g. 35-45 upwind), but the tack and gybe anywhere causes weird output ( e.g. 2 and -11 upwind). Thanks!

Many thanks and apologies for novice queries!

Thanks!







Sorry Nav and Perf polars are the same.

Last edited by eb12345 (8/06/2021 11:24 am)

     Thread Starter
 

8/06/2021 1:05 pm  #10


Re: Grid routes - avoid land

Numbers in parentheses indicate tacking or gybing. They are drawn on the chart with dashed lines. It could be to stay in a lane of wind or favourable current for example.

For example (-12) is tacking upwind, with a port bias.

There is a description in the Expedition help.

The TG (tack/gybe) button on the ribbon is very useful, especially with the Isocrhonal routing.  It calculates the 'best' route and also one that tacks or gybes just at the isochrones.

 

 

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