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Future of Mr. Tides - Printable Version

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Future of Mr. Tides - AugustH - 10-09-2007

There are a couple of functions I'm thinking of adding to Mr. Tides in the 3.1 release (which I've not even started on, so don't get all excited). There have been many requests for a way to add stations, and I can see how to do this for subordinate stations (though it will require some changes to the XTIDE database engine). I can't really see how to add reference stations, the harmonic constants are too many to just guess at, and the only ones who have enough data to create them usually are very reluctant to give them away for free (read: England).

The other idea is Collections of stations that all open together. So if you're planning a trip, you can beforehand make a collection and see them all at once as you sail along.

Maybe I'll add closer integration with MacENC and GPSNavX, pulling GPS data from them to display on the map. I'm not sure on this one, it just came to me.

As more ideas come to me (or you, the reader, make suggestions [hint hint]) I'll update this post with my progress.

August


- ReeferJon - 10-09-2007

Please, please, please... Tidal Vectors in MacENC!!!!

I realise that this may be more of a point for GPSNavX than yourself, August, but to have direction of flow and strength at a specific time would be invaluable for passage planning.

I actually purchased Belfield's Tidal Plotter for Windows, just so that I can get tidal flows in the Solent where I sail (it's a fairly complex tidal zone) but I still use Mr Tides within MacENC for checking tides "on the move".

Here's a screenshot of the tidal vector functionality.

[Image: new-tide-diamond.jpg]

Don't get me wrong.. Mr Tides is a great application.. but this is the one area that's missing in Mac Marine Software.


- cyberhusky - 10-10-2007

Quote:Please, please, please... Tidal Vectors in MacENC!!!!

I realise that this may be more of a point for GPSNavX than yourself, August, but to have direction of flow and strength at a specific time would be invaluable for passage planning.

I'm waiting for this too...

with some infos like MaxSea does

http://comen.maxsea.fr/MaxSea/Products/Features/Tides+and+Currents/default.aspx

or precalculated passing route which takes into account tides and tidal streams, as shown here:

[Image: stream-example.jpg]

Manou


Interpolating currents - AugustH - 10-10-2007

NOAA explicitly warns against interpolating currents between stations:
  • Currents are spatially variable, thus predictions should NOT be extrapolated even to nearby locations. Interpolation between two nearby locations should NOT be attempted. Use of such extrapolations can be hazardous.(emphasis is theirs)[/list:u]

    Unless there is a flow model available that describes mathematically how the currents vary over time, it's impossible to take isolated stations and create a chart that accurately reflects the currents. The programs listed in the other posts must use very simple models, or the areas they cover are simple enough (not changing that dynamically over time) that they can form predictions based upon limited data. This is my speculation, though, as I have not looked at them.

    For example, up here in the San Juan Islands the currents are incredibly complex. The Canadian Fisheries service produced a book with about 90 separate images of what the currents do, based upon the tide height at a station and how long ago the high tide occurred. The images show currents that reverse flow in a short space, flows that spiral, and flows that change velocity dramatically over one hour. Modeling something like this requires hours of computer time, not something that we simple users can do.

    Look at this example and you can see why current vectors are something neither Richard nor I want to even get close to:

    [Image: Straits.png]



- ReeferJon - 10-10-2007

I do take your point about interpolation not being as accurate as the properly modelled tidal charts available from the official HOs. However the fact remains that a significant number of PC-based marine charting applications are able to provide tidal vectors. This means that..

(a) they're using a dataset similar to Mr Tides and interpolating it or

(b) they're plotting vectors from more detailed data than is available in the Xtide harmonics database.
Some cartography (certainly Maptech's BSB charts, and I believe some S57 charts) include additional information about the tidal vectors in the area that they cover.

So maybe this is a question that needs to be addressed by the charting software...


- AugustH - 10-10-2007

Or they are ignoring the NOAA warnings and interpolating between stations.

The commercial people do have access to harmonics that the XTIDE-based people (me!) don't have. That's been proven in England and Australia, and I suspect many other places aren't releasing new harmonics but I can't show this. So I don't find it hard to believe that the commercial programs can get current flow models from government agencies after providing some lucre.

Another suspicion I have is that the particular locations that have flows are simpler to model than the San Juan's. I'd have to compare their output for a long period of time with what Mr. Tides produces, and see if there's some correlation. But even after doing that I'd still have reservations about the accuracy of the model I'd come up with, and I don't know what resolution I'd use. The two pictures I've seen on this thread are fairly broad overviews, and I don't know how far down you can go to get detailed flows.

Very interesting thread!


- cyberhusky - 10-10-2007

Quote:The commercial people do have access to harmonics that the XTIDE-based people (me!) don't have. That's been proven in England and Australia, and I suspect many other places aren't releasing new harmonics but I can't show this. So I don't find it hard to believe that the commercial programs can get current flow models from government agencies after providing some lucre.

If commercial marine software vendors get access to harmonics from government agencies, wouldn't it be easier for Rich to get access too? Probably it isn't so expensive to get the data, and I would be willing to pay more for Mac Navigational Software if i included reliable tides and currents info.
On the other hand it could be that the data isn't just available to the public because of security issues, that is government don't trust free software? (Which is a shame because most genius applications are from the shareware/free market: Open-Office, Linux etc.)

Though this is just an idea.

Manou


- GPSNavX - 10-10-2007

MacENC does plot any tidal currents/streams that do exist in the S-57 data. Such tidal/streams are going to be average maximums.

There was further disucssion on using currents for routing in the 'Show optimal tacking routes' thread in the GPSNavX/MacENC forum.

So far MacENC has avoided interpolation of data (i.e. GRIB forecasts including current) because such linear assumptions will certainly lead to significant error.


- JoMeKe - 10-11-2007

GPSNavX Wrote:such linear assumptions will certainly lead to significant error.

...and the related liability. Though I too would love to see detailed current vectors overlaid on an electronic chart, I certainly understand the inclination to "not go there". It's one thing for a government agency to print that info, but a small software outfit with limited pocket depth is a different story.


- Coomkeen - 10-12-2007

Maybe I'm missing something here, but computers and software and data limitations aside, if we are not supposed to interpolate between stations, what does your average bloke do actually on the sea with a paper chart?

Ron