Tide Units

[HappySeagull]

@Thomas my first attempts (awhile back)... it works fine,as a link in O though today a silly window pops up asking me if I "want to save command line switches to the ini file"...something to fiddle with. I just haven't got 'round to XTIDE on windows yet...

@Stargazer here's the math to add to HARMONIC for Patos Island feet
newPATOS_FEET.zip.doc

you just paste it in above the original Patos entry about Line 392917: Patos Island, Washington You need a decent text editor.Not windows stuff at all. Get notepad++ portable light or whatever.

CHANGE the name of the ORIGINAL entry to Patos Island, Washington (2)...yes, just add (2) so the Harmonic.idx won't get confused between the two. and you can make O display this as metric by a similar entry in the idx...For me, it works.See?PS ignore the time bar-it's not 0400 here I'm not that interested! This computer is on a different clock.

[HappySeagull]

oh, wxtide is ok. It is just wanting to know whether to always open "real time" I think. seems fixed I don't know if it's being maintained anymore..it uses the same Harmonic.idx that OPCN does...that could be a negative!

[StargazerWA]

Happy,

Thanks for working on this, I am still not sure how to implement the files you posted. How do HARMONICS.IDX and HARMONICS work? Is one for primary stations and the other secondary?

I replaced HARMONICS.IDX with HARMONICSfeetandMeters.IDX I then edited HARMONICS and replaced the Patos Island data with the text from newPatos_feet.txt

Patos is now in feet and has the right shape but seems to be on the Canadian Datum ~ 1 meter higher than the US. The US tides look fine, but the tides just a short Distance from Patos in the Gulf Islands are all doubled up one in feet and one in feet and one in meters. The ones in meters are in front and seem to be on the appropriate Canadian Datum. The ones in feet I cant seem to be able to click on.

[HappySeagull]

@Stargazer

As I said, that's what the data gives for the place. I haven't any better. If you pore through the files, you may find something I haven't. Or integrate something you find. Or, you will have to write your own HARMONIC entry if you want a different base Datum. Please share it, when you do.
HARMONIC is the master. Harmonic.idx refers to it as to data, so any reference to a HARMONIC entry has to be exact as to name. Harmonic. idx also positions your tide icons, names the station in the GUI, and can create secondaries from the stations in HARMONIC. So,there are two types of entries in the idx....an example TNAP would be a direct reference to a HARMONIC station,so it is one line...The name will always agree with the HARM' I call them Primaries. The idx also has a lot of (example) " tNAP" yes, it's just the lower case that tells you and the computer to expect a second line which has some tweaks to apply to the Master,Primary, HARMONIC. Of course, the secondary has it's own position and name, in its first line. t,T are tides. c,C are currents the rest is as obvious, -well, not obvious, but it's OUTHERE

So, all the positions in the IDX have to be different. Unfortunately, in the original creation, the computer did not do this, because they weren't thinking of how they would display on a map! And the computer also tended to repeat itself. It Liked certain numbers after the decimal and applied them constantly... such that, it seems a bug when no matter what you do, a staion won't display, but OpenCPN doesn't like two close stations on the same latitude or even (I might as well think! )longitude.

# means it'll be skipped. For humans or searching purposes only, so you can make notes and so on.

You should keep copies as you edit of course. If I write a new entry, say for PATOS feet, I add it, not replace it....that explains why I wanted you to rename in HARMONIC, to keep the (2) for meters that is a general rule IN THIS AREA, but NOT elsewhere.But you'll see.

If we don't hear from you in a week, I'll send in the Disentanglement Squad.They look like a flock of seagulls and are there to call you down to the sea...

By the way, to repeat, just in case...OpenCPN only sees HARMONIC and Harmonic.idx, so you need rename things, as I said in above post.

in the Meters+Feet idx, they are supposed to be "doubled up".You now have Feet and Meters for these stations. They were covering each other in the originals. See? But you can Change that.There are 3 idx I made for 3 options.But you can easily suit yourself.

[HappySeagull]

oh, and checking the NOAA pdf for Seattle today:
Patos Island definitely stinks it's just bad, not about chart datum. but in Seattle

18
Sa
03:26 AM 11.2 VS OPCN 3:15 11.31
08:44 AM 7.0 VS 8:28 07.01
01:31 PM 10.4 VS 2:20 10.33
08:28 PM -0.6 VS 8:34 -0.57

so that's not so shabby, is it?

so find the rest of the stinkers, folks! Maybe they should just be #'d out.

[HappySeagull]

...and what the heck is "Hall's Boathouse" - any of you yanks know? It looks to be the Metric version of Finlayson Arm in Canada, to me .

[cagney]

Happy
Here is the latest (2011-12-30) HARMONIC file, converted from xtide with the "restore_tide_db" program.
It does not fit with "our" IDX file, but, still, the Harmonic constants should be up to date. Note this

#
# The harmonic constants used to perform tide predictions for
# locations in Canada are derived from sea level data made available
# by Marine Environmental Data Services, Fisheries and Oceans Canada,
# for public, non-commercial use. The predictions are not the same as
# those computed by the Canadian Hydrographic Service, which uses its
# own sets of harmonic constants.

Up to you to interpret....

HARMONIC_NF.7z.doc

Thomas

[HappySeagull]

Thanks Thomas! I'll play with that!

[HappySeagull]

Originally Posted by cagney

Happy
Here is the latest (2011-12-30) HARMONIC file, converted from xtide with the "restore_tide_db" program.
It does not fit with "our" IDX file, but, still, the Harmonic constants should be up to date. Note this


Up to you to interpret....

Attachment 37593

Thomas

I made a quick separate idx and HARM' for just two local stations and they worked well against CHS tide tables...mind you, O scored well, too. There are some others that might be handy ...

[HotRod]

I'm not sure if it has been mentioned before in this thread, but there should be two sets of harmonic files, one metric and one imperial...
I wonder if this would be hard to change in ocpn. It should change to what units you select in settings for ocpn.

Have anyone of you converted the harmonic files to plain metric?
I tend to break the files as I go along... Sort of given up...

[HappySeagull]

Hot Rod, if we could figure out how you're "breaking them", we could get you to do it! Thomas has shown the labour intensive method http://www.cruisersforum.com/forums/...tml#post887730 where the line in the header of the Harmonic and its second column needs converting ...

[HappySeagull]

Originally Posted by StargazerWA

Well its still not right Cagney, the copy and paste you posted had lots of numbers changed, more than the datum, units and J1. Using that section gave me a weird tide with the wrong shape. So I adjusted J1, datum and units only and made another discovery, they still didn't match up to say protide.com by ~3 feet.

That when I remembered that the Canadians use LLW and the US uses MLW for a datum. So most of the tides in the US San Juans had a slightly negative low today, in nearby Canada they all had around a plus 1 meter.

The tides in Opencpn seem to be a mixture of both US and Canadian tide stations in US waters. This is really evident for Ferndale and Cherry Point Washington only 2.7 nm apart. Opencpn shows a +1 meter for Ferndale and a -.31 feet for Cherry Point!

This begs another question for which I think I know the answer. If I am using Opencpn using a NOAA ENC chart only the US tides will accurate relative to the soundings correct? If I am using my Canada BBS chart only the Canadian tide table will be accurate relative to the soundings.

Normally a half fathom isn't important, but in some places in the San Juans it is. I changed Patos Island back to the original and will instead refer to the closest US tide station or us a iphone app if accuracy is important.

Thanks everyone for the help.

I still haven't found why the crossborder discrepancy is so big! Jackdale's is the only "conversion" I've found as : US is 1.5 feet higher ( he didn't mention his source..)
http://www.cruisersforum.com/forums/...tml#post707463
but the discrepancies cross-border are as you noted, often twice that...even while OpenCPN's tide calculator agrees well enough with other sources. I guess you're left with "Seagull Nav"- take a sounding and just apply the forecasted change to it...

[jackdale]

Originally Posted by HappySeagull

I still haven't found why the crossborder discrepancy is so big! Jackdale's is the only "conversion" I've found as : US is 1.5 feet higher ( he didn't mention his source..)

It is/was an approximation by a colleague.

Canada uses lowest normal tide. The US uses mean lower low water.

I looked at the tides for tomorrow for Bedwell Harbour (using Canadian tide tables) and for Turn Point (Error Message Page)
They are on either side of Boundary Pass.

Bedwell

0257 - 9.7
0825 - 8.8
1046 - 9.1
1921 - 3.2

Turn Point

2:52 AM 6.9
7:22 AM 5.9
11:11 AM 6.6
7:09 PM 0.5

This looks like a 3 foot difference.

[HappySeagull]

Well, you got elected as expert source, because after hunting around for the reason and shaking free of a mess of learned pdfs , you're it, because you gave a number.

CHS-Vertical Datums is how the CHS has it. I guess that the two countries picked a low tide they liked without considering each other. A waterfall- even a virtual one-makes a good border, I suppose...

But a 3 foot difference?...The semantics of "lower low water, large tide,or " Lowest Normal Tide" in Canada " VERSUS "Mean Lower Low Water" across the Straits just doesn't seem to add up to that. aaargh.

[HappySeagull]

...can somebody find the detail where that 3 feet is obvious? Overlapping Canada/US charts that differ in a drying rock for instance? I haven't found it yet....