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Hi all Thinking of a project. All 35040 data-points of Newlyn 2022 tide-gauge data - recorded every 15 minutes = 4 datapoints per hour. Graphed in-entirety it looks like this http://weldsmith.co.uk/nautical/230323_th_newlyn_22all/pics/tide_newlyn_height_all.png Idea is to sequentially "crawl" the data extracting the highest high and the lowest low of each tide-cycle, so can have a plot with two corresponding lines - the highest-high and the lowest low. That should extract 352 or 353 (/ (* 365 24) (+ 24 (/ 50e0 60))) ;; 352.751677852349 highest-highs and lowest-lows in the year of 2022 The data presenting the cycles of the tide should look like this sample from 22:15,08Nov to 00:15,10Nov. http://weldsmith.co.uk/nautical/230323_th_newlyn_22all/pics/tide_newlyn22_ctr30k.png Which is "smooth". But wind, waves, a boat going past the tide-gauge, etc. could mean the first "drop"/"increase" might not the highest / lowest of the tide (respectively). However, prior knowledge about the tide cycle at 6hrs 12~1/2mins hi-to-lo / lo-to-hi means you can finish the search by an hour or two after the expected highest / lowest. So - an overall approach and an algorithm... Anyone interested to participate in a group effort? Credit to the DCGLUG group. Languages by a mild preference for me would be Lisp or unix shell-script. However any other good selection could be considered. ?? This is in my series "Pointless processing of Newlyn tide data". It's a project for if I need an intermission from building renovation work. Lining it up for if that juncture comes. I'm not in the South West at the moment, by the way, so cannot easily be a meet-in-real-life collaboration. I've just sailed crewing a yacht on the Bristol Channel http://weldsmith.co.uk/nautical/230417_ph_to_mh/230417_ph_mh_wp.html "Voyage Portishead to Milford Haven" to give some idea of the type of connection I have - the connection between the data and the reality. By the way - half the crew were unsuccessful in maintaining a successful relationship with their last meal on that voyage. Despite deliberately timing the voyage to be on a neap tide. [ http://weldsmith.co.uk/nautical/230323_th_newlyn_22all/pics/tide_newlyn22_ctr30k.png shows overall the 2-week pattern of neaps and springs which my proposed algorithm and its output graphed would neatly present ] Digression note - text-editor emac's built-in function "phases-of-moon" lists the lunar cycles, which within a day enables you to know the nautical cycles of neaps and springs without having to go look up from the tide-tables. Springs are at new and full moons; neaps are at the half-moons - the "quarters" of the lunar cycle. So anyway; takers for a group project? Regards, Rich Smith -- The Mailing List for the Devon & Cornwall LUG FAQ: https://www.dcglug.org.uk/faq/