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ironman · 11-01-2022, 15:46

Hi everybody,

I'm trying to have the weather routing plugin take into account the currents.

I have downloaded separate grib files for the same region for the same time period: one for weather, one for the current (rtofs). However, the grib plugin only shows the current, and the weather routing plugin gives me a 'grib failed'. If I remove the current grib, the weather routing succeeds.

Does this sound familiar to anyone and how can I solve this?

Thx!

seandepagnier · 11-01-2022, 16:16

the grib plugin is supposed to be able to load two files one for wind the other for current for example.

it's been a while but it may be possible also to concatenate two gribs together into a single file as well.

ironman · 11-01-2022, 16:47

Thx! I concatenated the relevant .grb files and now I do see current and wind data concurrently in the grib plugin. However, the route that is calculated seems to be unaffected by the current, even though I checked Currents in the Configuration - Options tab. I would have expected the route to have an undulation in it reflecting the various transversal tides.

rgleason · 12-01-2022, 07:48

@Ironman

1. The newer Weather_routing manual is here now, the instructions for dual gribs with current are in #19 Two Grib Files
and see Grib_pi
Are you following these instructions?

2. What OS? What version of weather_routing and how did you install it?

We need to be sure this feature remains intact.

seandepagnier · 12-01-2022, 08:49

it has been a long time with few changes and I know currents are applied, so I am wondering if maybe the currents grib isn't valid at the time and location?

ironman · 12-01-2022, 10:54

Thanks for looking into this! I've tried this on windows, opencpn 5.5.11, weather routing plugin 1.13.19.0, grib plugin 4.1, both from the PIM; I will update to the latest in a minute and let you know if that makes any difference. The example below is when I used the #19 Two Grib Files method; this has the same effect as concatenating the grib files. First example is when I only use the weather grib, second example is when I use both weather and current grib.

ironman · 12-01-2022, 12:26

I have made various changes and now I seem to see a difference for the routing with or without current, so I guess the topic question has been answered. Thx for your help.

I have the strong feeling that with regard to current gribs I'm at the start of a learning curve though. For now, I'm only able to get current gribs with a 3-hour time step or more, which seems to be too coarse to use for routing in tidal waters.

Furthermore, I still don't recognise the tidal rithm in the result of the routing. For me, this does not give me the feeling that I can use this plugin to zigzag my way through North Sea windmill farms. Weather routing seems to be useful for longer passages, during which you can update the gribs from some satellite downlink. On such passages, tidal current is of less impact, but ocean currents are. In other words, if tidal currents are critical, this plugin is not useful.

Details: I updated to OpenCPN 5.6 and Weather Routing plugin 1.13.34.0. The key change was probably that the grib should cover a wider area, at least the blob of isochrones that the plugin presents. In my previous snipplet it can be seen that at first the current grib did not.