If you live on or visit the coast, you know how important are the tides. Apart from determining whether you walk miles over mud-flats to reach water, the weather often seems to change with the tides. But here in the UK, tidal forecasting is effectively controlled by two government trading agencies, who seem set on taxing that information, and making its access complicated.
In many other countries, you could have used David Flater’s open source XTide to forecast time and height of tides from the Antarctic Peninsula to Zanzibar. Predictions are made using localised sets of harmonic constants to synthesize the complex waveform of tidal flow, much in the way that additive sound synthesis creates a rich sound with harmonics by adding together the waveforms of ‘purer’ simpler sounds (Fourier synthesis).
There is now an iOS version which supports the Watch, in Selene’s Tide Watch (iTunes US only, $0.99). Sadly obtaining harmonic constants for locations outside the USA, particularly those in the UK, has proven so troublesome that XTide and Tide Watch now only deliver forecasts for the US.
Thankfully the excellent port to OS X, Mr. Tides ($10 shareware) still includes superb fine-scale coverage of UK locations, as do its commercial iOS siblings AyeTides (for iPhone) and AyeTides XL (iPad). Embarrassingly for Apple, the two apps offered in its Mac App Store – Charts & Tides and Tide Graph – only provide tidal information for the USA.
There are several other iOS apps which also offer good UK tidal information. Brainware’s World Tides 2015 (iTunes Store, £1.49) covers the UK, but not France, Canada, and many others. Will Townsend’s Tides UK (£0.79) uses the UK National Oceanography Centre’s harmonic constants to good effect, and the British Geological Survey offers anyTide UK Tides free, for which you will have to make in-app purchases to obtain tidal predictions and currents.
Although the harmonic constants for a large number of UK locations have been published for decades, the UK Hydrographic Office claims copyright over these and will not permit them to be used in software without a licensing agreement, effectively killing their use in freeware.
The other agency with its own proprietary data is the UK’s Natural Environment Research Council (NERC), which funds the National Tidal and Sea Level Facility (NTSLF), generates data from its own network of tide gauges, and licenses data derived from those.
Both offer their own software, for Windows only, of course. The Hydrographic Office’s TotalTide is a high-end professional product, but the leisure user may be content with the more basic web-based EasyTide and its free predictions for the coming week. If you want any more, you have to use its odd pay-per-use virtual ticketing system. The National Oceanography Centre offers its POLTIPS-3 product at prices starting from £165+VAT for a mere three year licence.
Forgive me if I misunderstand the situation, but both the UK Hydrographic Office and NERC (and partners) are funded from our taxes. Thus the tax-paying UK population is being expected to pay once to two different agencies to acquire tidal information, and a second time when we wish to make use of it – again to two different agencies.
Would it not make much more sense to merge the acquisition, analysis, and control of tidal information for the UK into a single organisation, which would then make that information available under similar open terms as those of the USA?
Or am I, as King Cnut (Canute) allegedly did, trying to stop the tide?
Rewritten from the original, which was first published in MacUser volume 20 issue 12, 2004.