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neaps / tide-predictor

Javascript tide predictor
https://neaps.js.org
MIT License
23 stars 7 forks source link

Water levels differ from the public tide predictors #149

Open landyrev opened 2 years ago

landyrev commented 2 years ago

Hey, @kevee! Thanks for a great lib.

I'm playing with tide predictions and noticed that water levels generated by neaps/tide-predictor are quite different from the ones I can find in other tide predictors.

As an example I'm comparing the Monterey, CA tidal station, 2022-08-19

Neaps results: High level at 2022-08-19T21:08:11.000Z is 0.711727... meters Low level at 2022-08-19T17:28:11.000Z is -0.0094... meters

US Harbors results: High level at 2022-08-19T00:13:00.000Z is 1.55... meters Low level at 2022-08-19T17:31:00.000Z is 0.85... meters

So, while the time is pretty correct, the water levels looks offsetted compared to public predictions.

kevee commented 1 year ago

Thank you, @landyrev! I've been heads down in other projects for the past few months but I'll take a look at this PR next week.

Quick question - did you include an offset when you passed the harmonic constituents?

noGAFAM commented 2 months ago

@kevee, indeed, with offset, namely data_sets.datum from a harmbase2 database it works. Any reason for not including this data by default?