Harmonic Files ...

[nohal]

Your wish noted, now we just have to wait for someone willing to fullfill it. Sorry, but if there was such a harmonic file freely available, it very likely would have been already included in the OpenCPN package...

[kevinvh]

Originally Posted by nohal

Your wish noted, now we just have to wait for someone willing to fullfill it. Sorry, but if there was such a harmonic file freely available, it very likely would have been already included in the OpenCPN package...

Thanks Nohal - I have searched everywhere to no avail. As I said, I am happy to do the editing if someone could show me how to change feet to meters for the affected stations.

[nohal]

All we have is the documentation already linked above. And I really can't read it for you. I know tide and current prediction looks like science. It is probably caused by the fact that it is kind of science.

[kevinvh]

Originally Posted by nohal

All we have is the documentation already linked above. And I really can't read it for you. I know tide and current prediction looks like science. It is probably caused by the fact that it is kind of science.

OK, I have worked it out. Use a text editor to change the HARMONICS_NO_US file for the reference station, in my case, "Tarawa".
1. Replace "feet" with "meters"
2. Multiply the 3.3000 x 0.3048 = 1.00584 and replace the old value
3. Multiply the Amplitude values x 0.3048 for K1, K2, L2, M2, N2, 2N2, O1, P1, Q1, S2, and NU2, and replace the old values with the new values (Amplitudes are the first row of numbers in each constituent)
4. Save the file
5. Remove the old HARMONICS_NO_US file in Options/Charts/Tides & Currents and replace with the modified file just created
6. Exit Options with "OK" and reboot OpenCPN.

The exact conversion factor for feet to meters is 0.3048

You can do the reverse to convert from Meters to Feet; ie divide by 0.3048

[kevinvh]

OK, done a lot more research into tide predictions and how they are calculated in OpenCPN.

NOAA publish the Harmonic Constituents for tide stations under their control - https://tidesandcurrents.noaa.gov/ha...ml?id=1814060#

The University of Notre Dame publish a Global Database of Harmonic Constituents - https://sites.nd.edu/william-pringle...auge-database/

Another website for obtaining Harmonic Constituents - https://doi.pangaea.de/10.1594/PANGAEA.896587

A database of Worldwide Mean Sea Levels can be found at - https://psmsl.org

The 1st three websites give you the Harmonic Constituents that determine the tidal wave form and amplitude. The https://psmsl.org website gives you the Mean Sea Level of each tide station relative to a common datum for the World.

From the above mentioned, the HARMONICS and HARMONICS.IDX files used by OpenCPN can be updated - it is a massive job and one that I am not willing to undertake. However, I will update the files for the Gilbert Islands in Kiribati, which is were I am currently sailing. Perhaps someone else with a lot more programming skills can update all tide stations relatively easily?

[kevinvh]

For those interested, attached are my modified Harmonics files - see Change Notes inside the files for details.

Note that I have set the MSL Reference Level to zero for the Tarawa and Abaiang Atoll, because all I am interested in is the relative tide changes (ie. difference between high and low tides). The official MSL Reference Level for these stations can be extracted from https://psmsl.org and replace the zero value for each station if you want the official tide levels.

Don't forget to remove ".pdf" from the file extension of 221220_Harmonics_KVH.zip.pdf before trying to expand the zip file.

[kevinvh]

For those interested, I have updated my Harmonics files for OpenCPN. The updates include:
# Added new station for Port Vila, Vanuatu from gesla.uhslc (31/12/2012)
# Updated Suva Harmonic Constituents from gesla.uhslc (31/12/2012)
# Added new station for Lautoka, Viti Levu, Fiji Islands from gesla.uhslc (31/12/2012)
# Changed Betio Harmonics Constituents to University of Hawaii numbers (gesla.uhslc)(31/12/2012), and 1.000 meter MSL (NOAA)
# Added new secondary stations for Betio and Bairiki, Tarawa, Gilbert Islands (gesla.uhslc) (31/12/2012)
# Added new secondary station for Taburao, Abaiang Atoll, Gilbert Islands
# Removed old secondary station for Tarawa, Gilbert Islands
# Set above stations to display in "meters" and set MSL reference level to 1.000 meter MSL (NOAA)

The ZIP file is attached - don't forget to remove the ".pdf" extension before trying to unzip.

[Gilletarom]

Originally Posted by kevinvh

For those interested, I have updated my Harmonics files for OpenCPN. The updates include:
# Added new station for Port Vila, Vanuatu from gesla.uhslc (31/12/2012)
# Updated Suva Harmonic Constituents from gesla.uhslc (31/12/2012)
# Added new station for Lautoka, Viti Levu, Fiji Islands from gesla.uhslc (31/12/2012)
# Changed Betio Harmonics Constituents to University of Hawaii numbers (gesla.uhslc)(31/12/2012), and 1.000 meter MSL (NOAA)
# Added new secondary stations for Betio and Bairiki, Tarawa, Gilbert Islands (gesla.uhslc) (31/12/2012)
# Added new secondary station for Taburao, Abaiang Atoll, Gilbert Islands
# Removed old secondary station for Tarawa, Gilbert Islands
# Set above stations to display in "meters" and set MSL reference level to 1.000 meter MSL (NOAA)

The ZIP file is attached - don't forget to remove the ".pdf" extension before trying to unzip.

File usage test: Ok.

Data validity: I can't say anything.

[Maelruan]

Originally Posted by kevinvh

This is way beyond my capabilities. I just want a Harmonics.idx file with all data in METERS. Currently, it is a mixture of meters and feet.

I would be happy to edit the file if I knew what factors to apply at each station to change from Feet to Meters. Seems that it is not as simple as multiplying feet by 0.3048 to get meters.

Irish tidal data

Real time water levels for some Irish ports can be accessed online, and links can be embedded on the OpenCPN screen to be accessed when within mobile phone range on approaching that port. These data are uploaded automatically from tide gauges every 5 mins, and historical archives are available from these sources to allow harmonic calculation. The example in the attached screen grab has a mark using the Sea-DepthA-Red symbol near the entrance to a shallow channel thru' shifting sandbars, with direct links to water level gauges, including to data for that port's Irish Marine Institute's tide gauge at Tidal Observations | Marine Institute. Tidal height predictions there using UK tidal harmonics are usually out by from 20 to 50 mins, as well as full tide depth errors. VTS in large commercial ports convey readings from their local tide gauges to ships via VHF, and in many cases their gauges are also online.

In the link mentioned by Nohal the only source mentioned is an agency which looks after, inter alia, inland flooding, and so has gauges in some estuaries. On the other hand, the Marine Institute has more marine specific data, and also uploads IMOS weather buoy data, and high resolution 3 day tidal gribs the seas around Ireland and the English Channel, see Ocean Forecasts | Marine Institute.

Another marine agency with realtime online info is Irish Lights whose weather buoys report on Twitter every 20 mins, see: https://www.irishlights.ie/technolog...an-charts.aspx. These buoys are charted so links can be embedded on the OpenCPN screen beside them, and a similar process should work with any modern coastal weather stations elsewhere.

[P_Dub]

I have done the analysis of more than 40 stations in Ireland and the results seems OK to me. As I don't want to come in conflict with your Institute, I can not give it at large. So if you think it is better to use their data so be it.
So long.

[rgleason]

Originally Posted by P_Dub

I have done the analysis of more than 40 stations in Ireland and the results seems OK to me. As I don't want to come in conflict with your Institute, I can not give it at large. So if you think it is better to use their data so be it.
So long.

P_Dub please elaborate more. Your statement is too short to properly comprehend. Perhaps a little more context would help. Thanks so much.

[P_Dub]

In the past the leader of OpenCpn and those doing the harmonic file had to removed the Europeen data, in order not to come in conflict with tidal Institutes of other countries predictions, so we have to be careful with that.
Happy New Year 2023 Rick.

[Maelruan]

Originally Posted by P_Dub

In the past the leader of OpenCpn and those doing the harmonic file had to removed the Europeen data, in order not to come in conflict with tidal Institutes of other countries predictions, so we have to be careful with that.
Happy New Year 2023 Rick.

Please see: https://www.marine.ie/site-area/data...ta/access-data
"The MI Data Policy seeks to promote access to its data archives, subject to conditions under which data has been collected. In this context, we are working to make as much data available online as possible."

[fxykty]

Hopefully this isn’t a thread hijack, so here goes. If it is, sorry.

OpenCPN seems to encourage and be happy with multiple harmonic files. What does it do when the same tide station is in both data sets? Is there an ordering based on which set is higher in the list?

I’m currently using the default dataset (great that it now contains more international stations) and I’ve added the Terry’s Topics dataset. They seem to play nicely together. Or am I setting myself up for failure?

[kevinvh]

So long as the harmonics files have a different lat/long, they will appear in seperate locations on the chart. Don't know what will happen if they have the same lat/long. I will do a test.

What are the Terry's Topics files you mentioned?