Cannot see Tidal Stream for English Channel

[Rasbats]

Paul,

Some background. My OTCurrent plugin (OT) was a development from another plugin (tcurrent (TC) - now discontinued).

TC used paid for licensed data from UKHO. The use of this data within an opensource program was suspect, from the OpenCPN GPL licensing aspect. However TC did a lot of what you are suggesting, but not calculations of CTS/VMG. The licensed data came from the tidal diamonds shown on UK charts, where the data is sourced from the UKHO. This allowed tidal streams to be portrayed as arrows showing direction and rate. It was possible to select time and date and display the current hour by hour. Rotary tidal currents, such as those around the Channel Islands, could be shown.

OT uses the tidal current data from a harmonics file. Again it allows date/time to be selected and stepping through time, hour by hour. However, a limitation of these harmonics is that only two directions of stream are possible, ebb and flood. They are a good indication of direction for some areas but can be limiting for areas of rotary current.

I am working on a commercial server program, that can be accessed by an OpenCPN plugin. Unfortunately this is the only way I can access licensed UKHO data and fully comply with the OpenCPN GPL license. The plugin will work in a similar way to the S63 plugin which allows access to paid for commercial vector charts, with the opensource plugin working alongside a closed server program.

Mike

[CarCode]

Originally Posted by paul2

Do you know the validity dates for the 2013 dated French V9 file ?

You may read XTide: Harmonic tide clock and tide predictor or contact Daid Flater for this.

Gerhard

[conachair]

Originally Posted by paul2

...... , then design an engine to :
a) every minute or so, cycle round each Stream Marker within the displayed Chart area, and overlay the chart with the Strength/Direction (with suitable declutter) for the current time, as interpolated between the pair of encompassing hourly reference data rows, and
b) use a similar technique to iteratively build ETA & CTS segments of the Route, using datasets from the nearest Stream Markers closest to rhumbline of each route segment. The ETA/CTS could be run just when creating/editing the Route for static result, or selected to update every 10 minutes or so when under way, depending on duration of Route-Segment or a user setting.

It would certainly be an interesting exercise, though I wouldn't expect the data to be reliable enough to produce results accurate enough to justify the effort. It would need to be interpolated from the hourly data anyway then atmospheric effects can change things radically as well.
Still, interesting

[rgleason]

Perhaps UKHO reguards this data historically as a component of the defense for an island nation. Too bad it is not more public. Isn't there some way to improve the situation?

[conachair]

Originally Posted by rgleason

Perhaps UKHO reguards this data historically as a component of the defense for an island nation. Too bad it is not more public. Isn't there some way to improve the situation?

Unlikely.

Still, it's all, freely available, just mostly graphical so you need to do you own course to steer. Not hard really. But good idea to get it right in the alderney race
Tide Stream - Channel Isles - Monty Mariner - Monty Mariner
visitMyHarbour.com Articles


This one is interesting to see what goes on..
Kart – yr.no

Also here to see actual tidal heights against predicted, then can vary a lot depending on local weather conditions - don't completely trust the predictions!

Real-time data – UK National Tide Gauge Network | National Tidal and Sea Level Facility

[paul2]

Originally Posted by Rasbats

Paul,

Some background. My OTCurrent plugin (OT) ....

OT uses the tidal current data from a harmonics file. .... However, a limitation of these harmonics is that only two directions of stream are possible, ebb and flood. They are a good indication of direction for some areas but can be limiting for areas of rotary current.

I am working on a commercial server program, that can be accessed by an OpenCPN plugin. Unfortunately this is the only way I can access licensed UKHO data and fully comply with the OpenCPN GPL license. The plugin will work in a similar way to the S63 plugin which allows access to paid for commercial vector charts, with the opensource plugin working alongside a closed server program.

Mike

Thankyou Mike for casting perceptive light on the problems in displaying Tidal Streams for OCPN, from which I can see you also have been severely hampered by UKHO restrictions. Is the French HO more liberal with their tidal data ?

What you say supports my suspicion the harmonics method will not accurately model complex streams such as those in the Channel Isles.

Some questions on your current work. My preference is for enhancing OCPN so when well outside Internet coverage, it can accurately display Tidal Streams, preferably using Stream data to give more accurate CTS/ETA for each Route-Segment. Am I right in interpreting your description of your program (be it a plugin or fully integrated) is a 'Server/Client' within OCPN, serving OCPN Client modules eg Chart overlay to display each Stream Marker, and perhaps the Routing Software module to compute CTS etc. ?

Sounds like your program be unable to accurately model the rotary streams, due to reliance on harmonics ?

Have you looked at any of the Tidal Atlases (eg SailGrib, Plan2Map by C-MAP) on the Google Playstore for inspiration ?

You mention the program being commercial. How does that fit in with OCPN ?

As mentioned in my earlier post, I have time for just 1 more Channel crossing, after which will probably be another 2 years before chance for more sailing, quite short of time now. Any estimate on when your program likely to be ready ?

Glad you mentioned VMG. When racing, that's usually the most important figure I have displayed on my Garmin handheld. When there is a laptop onboard, I value software that prominently displays Heading, CTS, VMG to the Mark, COG, to lesser extent SOG, Distance-To-Go. It amazes me some expensive Raytheon Plotters do not show this.

I am not familiar with the S63 plugin as only briefly played with OCPN. As explained, I found SeaPro expensive to keep updating, and so moved to Garmin's MapSource in around 2003, which also had high-resolution vector charts with advantage they were uploadable to my GPS. Having paid for them, it is a shame I cannot read those Charts in OCPN ! It seems the Garmin API is published, as I read KAP files have been 'converted' to MapSource vector format and uploaded to Garmin for display. So maybe a reverse conversion can be done.

I see my thread got auto-tagged with English Channel. I would like to see a list of existing tags and add 'Tides' and Tidal Streams' to this thread. But I have used the forum so little, I cannot see how to do that. I read about Tags in the FAQ and it says I should see a box for picking or adding tags at bottom of the screen. But I have not seen it. Maybe it is only shown when starting a new thread.

I would be interested in hearing of your progress

[paul2]

Originally Posted by rgleason

Perhaps UKHO reguards this data historically as a component of the defense for an island nation. Too bad it is not more public. Isn't there some way to improve the situation?

Maybe; there was an episode of the BBC TV fictiional detective series 'Foyles War' where a German submarine put ashore a spy in an inflatable dinghy where he landed in the wrong place because they didn't account for the current.

Seriously, as paper Admiralty Tidal Atlases been on sale for ages prior to software versions, it is public knowledge. Think the problem is UKHO have always been very conservative. They were in prime position but missed a golden opportunity to make and sell a good PC Navigator product in the'90s when a number of PC Navigator products launched. Late in the day they sold their poorly received 'ARCS' product using raster scans of their excellent paper charts. Their conservatism is holding back others from making more useful navigation software. As tidal data has probably been collected over centuries, I would have thought any copyright on much of the data expired by now. Two other points: a lot of detailed tidal stream data has been collected from fishermen pre-war so dead by now. Similar data probably held by the French HO for the whole of the E.C. and it is actually the French side where tides are strongest so don't know if they are as restrictive; probably so otherwise navigation software could use their data.

[rgleason]

PAUL2
I see M Rasbats replied. He is quite experienced with tides and has developed several plugins for tides and they are quite useful.

Also there is a fellow developing and Admiralty tides plugin, which I've been building and testing, but we are just working our way through getting it to work, so I don't think that will be of use to you short term.

Mike's website would be an excellent planning tool I expect.

[Maelruan]

The EU MyOcean programme has developed tidal stream data for all EU waters. Some subsidiary developers have provided segments of this data in grib format readable by OpenCPN. The Irish Marine Institute grib downloads include the western part of the English Channel - 27MB for 3 days (see: Ocean Forecasts | Marine Institute).

The Android app Sailgrib now also uses this MyOcean data as an inbuilt standard so it no longer requires tidal stream gribs to be downloaded. The app's Weather Routing routines work very well, and the resulting calculated route can be imported in GPX format into OpenCPN.

Henri of Sailgrib says he finds the MyOcean tidal stream data to be quite accurate for the seas off the north Brittainy coast, but for the Irish Sea I have found their velocities well below historical observations. Up until the advent of Windows 10 I was able to display the VisitMyHarbour tidal diamonds (UKHO) on the same screen as the MyOcean gribs which allowed the discrepencies in tidal stream velocities to be very obvious. In some tidal races MyOcean was dangerously low! However I believe these problems were due to low sampling periods and are now being addressed.

It's a great pity we lost PC Maritime which I was still using it up to Windows 95! The optimum time of departure feature was great, & modern WR plugins & apps would benefit from that.

[rgleason]

Maelruan, what a great suggestion. Sailgrib and Sailgrib wr are some of my favorite grib apps and Henry has been a very active developer on android.
I use sailgrib all the time and think his EU current implimentation would be good.
Thankyou for sharing that?

[Rasbats]

A very useful discussion. To clarify some issues with the proposed update for tcurrent_pi:

Some questions on your current work. My preference is for enhancing OCPN so when well outside Internet coverage, it can accurately display Tidal Streams, preferably using Stream data to give more accurate CTS/ETA for each Route-Segment. Am I right in interpreting your description of your program (be it a plugin or fully integrated) is a 'Server/Client' within OCPN, serving OCPN Client modules eg Chart overlay to display each Stream Marker, and perhaps the Routing Software module to compute CTS etc. ?

The new plugin will use a server program that is completely outside OpenCPN, in the same way that the S63 plugin uses a black box 'exe' that is closed source.

Sounds like your program be unable to accurately model the rotary streams, due to reliance on harmonics ?

Rotary streams can be displayed by the plugin because the UKHO data is the same as that for tidal diamonds. Harmonics are not used for the streams. The data does not need to be downloaded from the Internet.

Have you looked at any of the Tidal Atlases (eg SailGrib, Plan2Map by C-MAP) on the Google Playstore for inspiration ?

See the screenshot at the end.

You mention the program being commercial. How does that fit in with OCPN ?

The new plugin will use the same model as S63 (Licensed vector charts). The plugin code will be opensource but the external server program has to be a black box because of access to licensed data.

As mentioned in my earlier post, I have time for just 1 more Channel crossing, after which will probably be another 2 years before chance for more sailing, quite short of time now. Any estimate on when your program likely to be ready ?

We are testing at the moment. Hope it can appear at the beginning of next year.

Up until the advent of Windows 10 I was able to display the VisitMyHarbour tidal diamonds (UKHO) on the same screen as the MyOcean gribs which allowed the discrepencies in tidal stream velocities to be very obvious. In some tidal races MyOcean was dangerously low!

Maelruan ... thanks for that feedback. The new plugin uses the same data from VisitMyHarbour.

My coding skills are pretty basic. Perhaps a JSON feed of tidal arrow data for a particular date/time and plugin messaging could allow a routeing plugin to calculate CTS/VMG? This would only be as good as the density of tidal arrows allowed.

Mike

[rgleason]

The plugin I mentioned is a work in progress is here. Currently it is not building, has several errors. It did build before but there was a problem getting to enter data or access.
https://github.com/registry/admiralty_tide_tables_pi

Hopefully it will progress.

[paul2]

@Maelruan & @rgleason

Before revisiting the forum yesterday, by coincidence I had been perusing the many Tidal Apps on Google PlayStore - there are so many it took many hours reading descriptions of any that look remotely useful - before even starting to search for independant reviews. 3 that looked worthy of further investigation were :

1) 'Marine Weather | SailGrib' 4.3* free but adsupported He also has £6.00 one 4.6* but difference not obvious, also has a OCPN rival that is huge and includes E.C. Tidal Atlas -so at least 3Versions - French developer;

2) 'Tide 7 UK' 4.0* £1.29 no-Ads- claims to use full Admiralty EasyTide service, but no Atlas? - UK developer;

3) 'Plan2Map' by CMAP free - claims to have 'Dynamic tides & Current Predictions', also dl free 5 day WX overlaid onto chart - a rival to OCPN in that it also has Route Planning & instrument display- Global company.

So in addition to my short ref. to this in my reply yesterday to Rasbats, I intended to ask if members generally have come across any good, preferably cheap or free Android Apps that show a central E.C. Tidal Atlas in chart layout with resolution approaching the Reeve-Foukes ?

Of course the above are standalone programs unconnected with OCPN, even the Android version of OCPN. But as the Desktop OCPN version does not appear to use Tides in its Routing data, and the Tidal Stream overlay being crude compared to Tidal Stream Atlases, paper or SeaPro, I thought to look if there were any Android Apps that showed a good hi-res Tidal Atlas.

On subject of Android OCPN, I see there are 2 programs with same name & logo -(neither free) but only 1 is by same developer as Desktop OCPN. Does anyone have any experience or reviews of the 'official' Android OCPN ?

I have a quite small datacap on my 3G internet provider, not much time left for 'suckit and see' install/uninstalls so any recommendations (in addition to earlier mention of SailGrib in general) on which of the above 3 (or any that I missed) is best for Tidal Stream Atlas format and central E.C. resolution would be appreciated.

Re. reference to PC Maritime, yes I remember using 'PC Wayplanner' which I think was from them, a pre-Windows 'DOS' program on floppy disk. Apart from the all-important CTS correction, that bargraph was great for quickly illuminating best and worse times to depart - so obviously had a good tidal database - why have we lost all that ?

RE. Windows 10 DON'T ! My first MS Windows was 1.03, my most liked was XP, moved to 7 only 3 years ago and will stay on it as long as poss. Quite apart from MS exhausting my datacap with downloads AND uploads, I read somewhere if 10 can't find an internet connection within a certain period it will stop working.

Many thanks for your posts.

[paul2]

Originally Posted by Rasbats

[COLOR=RoyalBlue]A very useful discussion. To clarify some issues with the proposed update for tcurrent_pi: ....
Mike

Sorry Mike, I missed your reply until just now. Although your post timed earlier than my last reply, it didnt show until later - maybe a moderation delay.

The screenshot of Channel Isles streams with strength & direction looks very encouraging.

Looks very good density of arrows and I like the colour and size coding for strength. It might be an idea to reduce the size a little as I notice the 0.8Kt arrow still a good size, so unless your smallest arrow already v. slim, there's scope to scale down a little.

Also I notice no arrows for Alderney Race. That is often a crucial place for decision point on whether to buck tide in the Race or go the long route outside the Casquets. When I posted my test to check if OCPN used tides in its CTS calculation, I chose Alderney Race because the French Harmonics V9 said 8kts running through it at time of the test, and V9 had a pair of arrows towards the W. & E. ends between Alderney & Cap de La Hague showing slightly stronger flow on Alderney side. So good idea to add a pair of arrows at same spot if that is possible.

I will look forward to it in time for my next return

[Maelruan]

Paul2,
Yes that was indeed PC Wayplanner which could work on a DOS session of Win95.
I concur with rgleasons remarks re Henri of Sailgrib WR. I'm attaching a routing I've calculated for Sandbanks to Guernsey leaving at 0630 next Wed 24 Aug 2016 using the Polar for a Dufour 24 and the Arpege Europe weather grib Henri's app provides links to. My present Sailgrib config saves this as a KML file, so I imported it into Google Earth from the Sailgrib/Routing folder on the Android. I then copied it as a track in Google earth and pasted it directly into OpenCPN, which has the facility to export it in turn as a GPX file, which is also attached.