Strange Diffs in Tidal Height Calcs Using Harmonic.idx from wxtide32

[globalkeith]

An example (using the same harmonic.idx file):

Location: Canton River: Nei-ling-ting
Hong Kong, China + Corrections: High(+2:05 +0.60) Low(+2:05 +0.60)

Date: 2012/05/15

Using wxtide32:

L 0110 0.9m
H 0832 1.8m
L 1344 1.4m
H 1929 1.7m

Using opencpn:

02:18 -12.30m LW
09.23 112.74m HW
16.45 01.99m LW
21.56 68.56m HW

The values aren't even close? Am I missing something?

The values in the harmonics file are:

tAsi:Chin:: 113.8167 22.4167 8:0 Canton River: Nei-ling-ting
&125 1 0.6 1111 1 111.1 1509 2 Hong Kong, China


So whats up here, any ideas how I can correct? I can't quite see it...

thanks in advance...
Keith

[nohal]

Keith...
Isn't WXTide using tcd database (harmonics-2004-06-14.tcd on my machine), so the harmonic constants are possibly totally different from those in the HARMONIC file in OpenCPN unless you converted one to the other? HARMONIC.IDX is in neither case where the tidal data are stored, it's just a list of locations.

Pavel

[globalkeith]

Hi Pavel,

Yes, you're right that wxtide is using tcd.

I downloaded this http://fserv.skill-club.com/get_1088_156a.html for use in opencpn - this gives me the 130m tide for that location - clearly there's an error somewhere -

I understood the .idx file to contain offset values for secondary locations - "Canton River: Nei-ling-ting" is based off the "Hong Kong, China" reference station.


# Subordinate sta'ns: t|c Reg:Co:St Lon Lat Meridian Name
tAsi:Chin:: 113.8167 22.4167 8:0 Canton River: Nei-ling-ting

# Subordinate extra:
&Hmin Hmpy Hoff Lmin Lmpy Loff StaID [tzname] RefFileNum RefName
&125 1 0.6 1111 1 111.1 1509 2 Hong Kong, China


I've just updated the .IDX file to the following values:

# Subordinate sta'ns: t|c Reg:Co:St Lon Lat Meridian Name
tAsi:Chin:: 113.8167 22.4167 8:0 Canton River: Nei-ling-ting

# Subordinate extra: &Hmin Hmpy Hoff Lmin Lmpy Loff StaID [tzname] RefFileNum RefName
&125 1 0.6 125 1 0.6 1509 2 Hong Kong, China


Not sure if thats the correct values yet, I'll do some investigations but it now shows a tide height of around 2m which is closer to the mark.

thanks
Keith

[nohal]

Keith...
The values for that substation are obviously way off, there sure was no 100 meter tide the last time I passed over there But at least I don't have access to a reliable source of better data with a license allowing us to do anything about it.
In the different HARMONIC files you find over the net, the accuracy and number of errors will sure vary a lot - you always have to use common sense and check them against some official source before trusting them.

Pavel

[HappySeagull]

I haven't done much of this and I fiddle with currents more but I think you are "getting it " Global Keith...it's about this"&Hmin Hmpy Hoff Lmin Lmpy Loff StaID [tzname] RefFileNum RefName"
so Hmin is Highwater time diff in minutes Lmin is Lowwater, H/L offsets are slack water and Hmpy/Lmpy are tide height diffs (so watch out for that "1509 " I see above!) oh, and "-" ahead would be subtractions from the Primary( RefName), of course

but better explained here
About harmonic constants and sub station corrections

you've moved on from this and I haven't fiddled with this in a while but I think Wxtide can use ascii harmonics files...

from help:
"Harmonics file

"A Harmonic file contains the harmonic constant data for various locations throughout the world. There must be at least one or more harmonic files present with the program. WXTide32 expects this file to be called harmonic subject, of course, to the use of the HFILE environment variable and the -hfile option on the command line or in a config file or as specified in a harmonic index file."


"WXTide32 has the ability to read binary TCD format tide files. These files are smaller and faster than previous ASCII text files. ......."

from which I figured that it can read ASCII text files! and so an edited cfg file ...
-hfile "harmonic"
-indexfile "HARMONIC.IDX"
-userfile "userfile.idx"
is apparently working.

[HappySeagull]

...that is, I test it by removing all other tcd or msc files from the wxtide folder,so my HARMONIC and harmonic.idx are the only options...

and here's more than you want to know!
gleaned from a thread here...

"the whole voodoo about the conversion from wxtides "harm_msc" to opencpn's "HARMONIC.IDX" is to fill the missing fields with "x 0 0" "
that is... where msc has
M3 0 0
M4 0.002 300
M6 0 0
M8 0 0

OpenCPN has

x 0 0
M4 0.002 300
x 0 0
x 0 0

[P_Dub]

Happy you should not do like that, it is wrong to fill it in this way; it could lead to errors. You need to put the constituents correctly and 0.0000 (2 spaces) 000.00 that is for the value of the constituents and the angle of the constituents. This way it would fit OK. That is exactly the reason why things are not working correctly.
Bye

[sailorF54]

Re writing
x 0 0
for missing components

FWIW, the testers for the European tides data have nor reported issues that could be traced to that way of filling in missing components

[HappySeagull]

What I should not have done is add it to post #6...it's just a note that explains that all the x 0 0 stuff are placeholders, but it's not pertinent to the idx discussed. sorry.

[CarCode]

Anyone ever have had a look at GEZEITEN FISCH 2012 | Angeln an der Nordseekste <(((>< ?
I am wondering where this site gets its data from?

Gerhard

[HappySeagull]

CarCode, I had a glance in my area (BC Canada) The station names and especially the position errors are suspiciously like one of the databases OpenCPN, wxtide, and xtide have been known to use... but I haven't looked hard enough to see which of the possible sets that are kicking around they are using.

Are they better where you are? (in Germany?)
For tides Hereabouts, with a few tests , they agree with my present Opencpn set.

added They do some odd things with positions- a lot appear as xx degrees, xx minutes and 60 seconds! which would be a minute, so that's an interesting tweak, that is...

[P_Dub]

Happy, I have done all the English channel and North Sea to Germany (including France, south Coast of England, Belgium, Holland and Germany to Hamburg) and have found some differnces in many places when analyse with the CHS 146 constituents data. I did obtain the hourly and sometimes the 15 minutes data from the respectives Authority, of each country. Generally they don't like that someone publish data without their permission and I suppose that Xtide people did so. Presently, I am building a file converter in Visual Basic that could take care of the conversion into the 175 constituents list of Xtide. If we succeed to do something decent we will let you know. The program that was send to me in C++ does not do the job properly. So you will have to wait.
Regards

[HappySeagull]

Wow! That's great!, P_Dub!

Idea...One of the nuisances of the OpenCPN database is that it is not sorted as to Country or even coastline. It'd be much easier to maintain and replace different areas if it was. Especially as, OpenCPN Betas can now load different databases on demand easily.
Loading or trying to correct portions of the whole world's tides at once seems pretty clumsy.

[globalkeith]

Hey guys,

I've created a new github repository for this kind of stuff

Please fork and contribute when you have time...together we can make this better

http://github.com/ktec/opencpn_extras