Tidal Currents (Not Heights)

[wizard-merlin]

I am new to creating charts, and thanks to this forum have been successful so far. I would like to be able to see tidal currents (direction and speed) on the chart, but am failing. Is there a way either to update the "harmonics" file with tidal diamond info from paper charts (i.e what is the format for the harmonics file ?) OR is there a way to create my own "GRIB" file and treat tides as "wind" in direction and speed ? I've looked around quite a lot and drawn a blank with both of these.

[nohal]

wizard,
have a look at Tides and Currents | Official OpenCPN Homepage
You have to be aware that the free data are not available for the whole world. To be more precise, you won't have currents if you are not in the U.S.
Grib can contain current data directly - the only source of free data I remember now is for Germany and areas around at Strömungen

Pavel

[wizard-merlin]

Thanks Pavel, no, I realise I can't get this data outside US. I note though that the Harmonics file is ASCII, and it should be possible (theoretically) to populate it with the data from my paper charts, if I could work out the structure. An alternative, which would give a nice visual display would be to create a GRIB file of tidal data, as you could jump through the time. This seems impossible, as GRIB creation seems solely UNIX based. So I'm back to understanding the Harmonics file to update it manually...

[sailorF54]

Originally Posted by wizard-merlin

Thanks Pavel, no, I realise I can't get this data outside US. I note though that the Harmonics file is ASCII, and it should be possible (theoretically) to populate it with the data from my paper charts, if I could work out the structure. An alternative, which would give a nice visual display would be to create a GRIB file of tidal data, as you could jump through the time. This seems impossible, as GRIB creation seems solely UNIX based. So I'm back to understanding the Harmonics file to update it manually...

This has been done (i.e. currents) for France by a friend of mine (Merak56 on french forum Hisse et oh !)
You can download the file here (tides + currents) (replace the harmonic and harmonic.idx files in tcdata folder for testing)
Easy to back engineer to suit (I've done it)
https://docs.google.com/leaf?id=0BzW...thkey=CJa1jJkK
Brown spots on chart + an example
However the display may be rather oversized due to current (no pun intended) limitations on OpenCpn (up to now, at least)
Also on French charts and documents (at least) the data (velocity and direction) is given separately for neap and spring tides. I understand that a single set of values is required in OpenCpn.