Weather Routing

[Taarnskov]

Pavel,
I agree with you, and this is the reason why i wrote the above. The climate data is very useful to judge the overall situation, but difficult to use in a mathematical model.

Lars

[rgleason]

Lars,
In this thread and the Climatology thread, with Sean participating, we had an interesting discussion about the algorithm to use with the wind rose and frequency data. One suggestion i made was to sum each vector X frequency to obtain a resultant vector which can be used for that grid location's calculation. I am not sure if Sean uaed that technique to accurately represent variability, but I seem to recall that he was concerned about processing time. After that I began to think that this algorithym could be preprocessed and become resultant vectors for each grid location, thereby reducing the size of the climatology data possibly (with loss of wind rose showing).

I do not know what Sean eventually did but i believe it is in the code and Sean indicated that what he had done was a first stab at it. Perhaps Sean will be able to advise further.

[Taarnskov]

Rick,
I remember the discussion about the algorithm, but we didn't get an answer from Sean. I do not mind long processing time on the computer in the planning stage, as long as we get the correct data for our decision-making.

Lars

[Bucaniere]

I apologize if I did not understand, but they are three days I read and I could not figure out how to use (and where to find) the plugin.

I use OpenCpn 3.2.2, I installed the latest version of the plugin Climatology with the updated database. Where can I find the plugin Weather Routing? (I suppose .dll?)

I apologize again for my English and thank those who want to help me.

[cagney]

I think that there is way to much emphasis on using the climatology plugin for routing. Never use climatology if there are gribs available!

I would even say, don't use climatology for wx routing, use it for general planning. Avoiding strong winds seasons, hurricanes etc.
Why? Because in most cases you will be fooling yourself. Seemingly accurate figures on the screen that in most cases are way out.
It is not a good idea to average widely different wx patterns, and use it for routing.

For example the route between Bermuda and the Azores in June. Predominant wind between SW and NW but occurrence of winds from any direction. The key to understand this route is wx patterns governed by the streamline pattern on the 500mb level. Two typical patterns Zonal flow or an Omega Block will give widely different surface winds. Using Climatology for routing will probably work with a zonal pattern, at least for a few days, but not necessarily at all with an Omega Block.

These wx patterns can persists for a week or two. If you have access to gribs, this will be part of the computer calculations.
If you don't have a sat-phone for gribs use wx-faxes for guidance. This will give you way better info than climatology.

For the routing plugin, don't present gribs and climatology as "equal" alternatives, because they are not.

Thomas

[rgleason]

Bucaniere:

- Where can I find the plugin Weather Routing? (I suppose .dll?)

You will need to run the most recent beta version of Opencpn 3.3.xxx and you can find the Weather Routing dll here Opencpn Beta Login -File thingie user: rguser pass: rgpass and look in the opencpn version directories listed.

Lars:

I remember the discussion about the algorithm, but we didn't get an answer from Sean. I do not mind long processing time on the computer in the planning stage, as long as we get the correct data for our decision-making.

Yes, I agree. I have found the Climatology routing very good for a spring voyage from Nassau to Newport and some other situations, with good results, but you have found some situations where the wind rose in a given month does not have a definitive direction, and it is not as effective. It would be nice to improve that. I hope Sean will help us with this little problem.

Thomas:

...use it for general planning.

I agree, and in the Wiki writeup, there is a cautionary note about about this. You are absolutely right about a current grib file being a more accurate planning tool for the first 8 days, however it is known that grib files longer than that become too inaccurate because the weather changes unpredictably (these predictions may improve in time and become more useful), and that is when historical data may be a better choice, which is where the use of Climatology to extend the routing can be helpful as a general planning tool =/- many factors. (...perhaps there should be a fat red dot when the data source changes.)

Also both grib files and climatology wind and current files should be taken with a "grain of salt" as they say. They are only an imperfect tool which hopefully will get better in time through testing, modification, use and experience. See the warning about the use of the data here

It is wonderful that Sean has spent the time and effort to provide us with this first tool which can be improved... I have found it useful as a very rough guide. Your actual route will inevitably vary dependent on conditions and decisions made during the voyage.

[rgleason]

RE Lars post above: South of France to Gibraltar in April 2014

I agree with your assessment. It could be the short 4 day, or a longer voyage, dependent on current weather patterns. The wind roses are variable in that time frame.

Perhaps the routing should show a short favorable estimated route in blue and a long unfavorable estimated route in green, with some weighting of which one is more likely?

Another alternative might be to show a route with a predicted broad swath of variability which indicates position every 3 days or whatever, but I am not sure how that would be calculated.

[cagney]

Originally Posted by rgleason

RE Lars post above: South of France to Gibraltar in April 2014

I agree with your assessment. It could be the short 4 day, or a longer voyage, dependent on current weather patterns. The wind roses are variable in that time frame.

Perhaps the routing should show a short favorable estimated route in blue and a long unfavorable estimated route in green, with some weighting of which one is more likely?

Another alternative might be to show a route with a predicted broad swath of variability which indicates position every 3 days or whatever, but I am not sure how that would be calculated.

OK, I'll continue with my rant for a bit

It's futile to even try to use Climatology or a Pilot Chart for such a short trip. That is not their intended use. Check the synoptic charts, and gribs, if available, and use your meteorological knowledge. Also don't forget broad-casted forecasts.

For actual routing, the choices are very limited, with Land on one side and a couple of major islands in the way. It will be down to the actual conditions at the time.

Climatology will probably tell you that it's a better idea to make the trip in July instead of in December though.

Climatology is the average of all observations for a month and as such the average of all wx patterns, but says absolutely nothing about the weather pattern for your trip. Imagine the difference between the weather with an established High in the area, versus a patter where one low after the other is tracking across the bay of Biscay.

</rant>

Thomas

[rgleason]

Thomas, I don't think this is a rant, they are very good points which need to be considered when using Climatology effectively. I would be nice however to get some idea of the range of variability in the routing possibilities, and range of duration of the voyage. There must be some effective way to compute and show these factors.

[Bucaniere]

Originally Posted by rgleason

Bucaniere:
You will need to run the most recent beta version of Opencpn 3.3.xxx and you can find the Weather Routing dll here Opencpn Beta Login -File thingie user: rguser pass: rgpass and look in the opencpn version directories listed.

Thank you very much, now I understand!!

I will try to use plugin with grib and not with climatology, because my sailing area is too small and influenced by local winds.

[rgleason]

Bucaniere I encourage you to become familar with Climatology as it has an extensive database of other data types than just wind which may be useful

[cagney]

Originally Posted by rgleason

Thomas, I don't think this is a rant, they are very good points which need to be considered when using Climatology effectively. I would be nice however to get some idea of the range of variability in the routing possibilities, and range of duration of the voyage. There must be some effective way to compute and show these factors.

To use Climatology for actual routing, as opposed to general planning, is actually not smart at all. Why? Because we throw all knowledge we actually have overboard, and choose to start in a vacuum.
If you are in Southern France and plan a trip to Gib, you do know a few important things. The wind direction now, wind-strength and how the weather has developed the last few days. Why not use it?
I can see a few ways to process available data. The simplest is to compute the route, starting with the present conditions. If I have SW wind 10 kts now, what is the most probable development? This of course requires a lot of number crunching.
The next step is to use the current wx pattern, and probable development. Exactly how to do this can easily get complicated.
The 500mb streamlines steers the wx pattern in temperate latitudes, the track of Lows etc.
To relate 500 mb pattern to climatology different databases probably have to be cross-referenced. This of course requires a massive computing effort. It's not difficult to see that this quickly gets very complicated, and hardly worth it.... or?

Thomas

[rgleason]

Thomas, each to his own. Having invested considerable time on the data aspects of Climatology for Sean, the developer/programmer, I am not ready to agree with you about the usefulness or lack thereof of this tool. It is still in its early stages and will be improved over time.

I am still going to use it for planning, as it supports use of Grib files of any length for the start, then the Climatology data is used to extend the route.

It does find the traditional trade routes as it stands, and it does give some estimate of voyage time. I am not sure how Sean calculates the polar data from basic boat characteristics, but in time we will understand where improvements need to be made.

I agree that tracking and anticipating weather is key, and that considering and anticipating 500mb and troughs will help with this forecasting. I do not know how that data can be brought into climatology yet, but we do have the Weatherfax overlay tool which Sean created first, which can assist that inspection.

I have no doubt that these plugins can and will get better, but right now Opencpn is the only program I know of that has some of these tools, such as Climatology.

[rgleason]

Please refer to this technique to use Visual Passage Planner to calculate passages over end-of-the-month boundary - the workaround is make two voyages and have the software calculate them for the respective months.
http://www.cruisersforum.com/forums/...ml#post1067854

Also this easier start date technique is suggested for Visual Passage Planner by the software author.

How could this be done with Climatology & WxRte? Is there a way to have more control, or perhaps to know what is happening?

Here is the question every one asks about Route Planning software, Climatology & WxRte plugins too ...by conichair with barnakiel's reply following making a reasonable case for climatological data being used as a planning tool, but not for actual routing during the voyage.

An couple of brief plugs and reponse for Climatology & WxFx in Visual Passage Planner thread. Cagney says both plugins are promising...

After trying V.P.P. list to things I like about it . repeated here so that we can improve Climatology & WxRte.

In Visual Passage Planner, I like:

Simplicity and ease of creating a routing.
Instant Report with Route information and averages.
Additional data types of Dew Point, %Heavy Icing and % Light Icing.

I particularly like the Preference item for Method of Calculating Wind speed and direction during simulation of passage.

1. Use weighted average of all occurrences
2. Use highest percent occurrence.

I think it is perfectly reasonable to have two or three methods of calculation to apply to most appropriate one for the route, in the judgement of the user, because it addresses what we have noticed with Opencpn weather_routing plugin's use of Climatology plugin data. The routing finds the trade routes, but in areas where there is a high degree of variability it tends to result in routings that are too fast, because I believe it is using a method like #2 above. Having several other calculation methods, one similar to item #1 above, which I suggested earlier (the summary vector could be pre-calculated and added to the database) might be very useful.

[seandepagnier]

Originally Posted by cagney

To use Climatology for actual routing, as opposed to general planning, is actually not smart at all. Why? Because we throw all knowledge we actually have overboard, and choose to start in a vacuum.

Currently it only makes sense in areas with very prevailing conditions. In these areas you don't really need a computer to route you normally so I agree it is currently virtually useless for most practical purposes.

Eventually the idea is the expand the climatology data to include more than just averages, so that with grib data, it can lock on to a past weather pattern, and make a better long term guess. Also possible is to show best/worst/average case scenarios etc..