Algorithms

12-Oct-06 11:47

This may just be lack of knowledge on my part... not sure if I have enough information to calculate this or not. I am googling right now, but not turning up anything on the specifics of my need but on all the side issues I alreay know.... Sigh | :sigh:

Okay... first what I need to do is calculate current ocean level minus wave motion. In otherwords the gravitational surface including the moon. I have already the gravitational surface of the earth (geoid) from NASA, and have had it for a couple of years now. I am one of the few people who use it. But I need to add in the tidal effect in ocean height based on the lunar cycle. Not sure if atmospheric pressure affects sea height noticeably, but I basically have a ship that I need an accurate height on and the ship based GPS locations seem to be putting out a very poor +-20 meter location even from one end of the ship to the other.

Theoretically I have proposed the following:
Using knowns (lat lon location, lunar distance and viewing angle from location, sea level based on gravitational surface of earth):
Calculate height of ocean based on pull of the moon
use this in a more accurate position.

I am not asking you to do this for me, but if you can point me to the right location, I will do it. I will keep googling various terms hoping to stumble across the calculation. No homework, I am long since out of school.

Thanks!
Jeff

P.S. yes, I live in a desert, ocean tidal effects are something I never had to worry about before....

_________________________
Asu no koto o ieba, tenjo de nezumi ga warau.
Talk about things of tomorrow and the mice in the ceiling laugh. (Japanese Proverb)

Dan Neely13-Oct-06 2:29

Dan Neely

13-Oct-06 2:29

I tried finding info on this sort of calculation some years back, but was told thata major factor in tidal heights vs time was the sloshing of water around terrain features that disrupted the simple newtonial effects that a water world would undergo, and that as a result there wasn't a theorectical model available.

El Corazon13-Oct-06 3:17

13-Oct-06 3:17

dan neely wrote:
and that as a result there wasn't a theorectical model available.

So I seem to be finding out... However, that in and of itself is good. This particular ship will not be sitting near terrain features, so I may be able to use the earth gravitational model with 1m effect from the sun, and 3m effect from the moon in the deep ocean. So I am not at a complete loss yet.

_________________________
Asu no koto o ieba, tenjo de nezumi ga warau.
Talk about things of tomorrow and the mice in the ceiling laugh. (Japanese Proverb)

Dan Neely13-Oct-06 3:36

Dan Neely

13-Oct-06 3:36

Maybe. This was a few years back, but the impression I got was that the sloshing didn't just effect the hieghts of the tides, but offset the locations of the bulges as well. IIRC there was mention of a large bay(sea?) that ended up with a 24hr cycle instead of the normal 12.

El Corazon13-Oct-06 3:46

13-Oct-06 3:46

dan neely wrote:
Maybe. This was a few years back, but the impression I got was that the sloshing didn't just effect the hieghts of the tides, but offset the locations of the bulges as well. IIRC there was mention of a large bay(sea?) that ended up with a 24hr cycle instead of the normal 12.

about my biggest worry will be proximity to islands... This will be deep pacific, it will never (as far as I know) be in an inland sea like the gulf of Mexico.

_________________________
Asu no koto o ieba, tenjo de nezumi ga warau.
Talk about things of tomorrow and the mice in the ceiling laugh. (Japanese Proverb)

fat_boy7-Nov-06 1:16

fat_boy

7-Nov-06 1:16

Jeffry J. Brickley wrote:
calculate current ocean level minus wave motion

If you are referring ot wind driven waves, then, unless the boat is in a fairly fierce storm, and quite a small vessel, this fluctuation can be ignored.

Jeffry J. Brickley wrote:
I need to add in the tidal effect in ocean height based on the lunar cycle

This will be almost impossible. Tides are extraordinarially complex. Some parts of the earth have virtually no tide (I mean in addition to the Med, which has no tide, some open ocean islands also have no tides). Other parts, like the channel islands, and th eBristol channel have as much as a 10 meter variation. Some places, like Southampton have two high tides.

This is all because water swirls and flows around the earth, dragged by the moon, and the way it moves is affected by land, and interfeerence wave paterns.

Additionally, when the sun and moon are in line larger tidal forces are generated.

I would say that calculating the height of a tide from the moons position would be almost impossible.

Instead I would refer to know tide heights around the world in relation to highwater Grenwich.

Truth is the subjection of reality to an individuals perception

El Corazon7-Nov-06 2:06

7-Nov-06 2:06

fat_boy wrote:
This will be almost impossible.

Very true... but at least in the process of learning it, I ruled out the need for it. This should be deep pacific only, even when they are around islands they should get only minor tidal forces. I am knew to tides (I live in a freakin' desert!), so I had to ask. Now I know, but that means one less calculation. Smile | :)

_________________________
Asu no koto o ieba, tenjo de nezumi ga warau.
Talk about things of tomorrow and the mice in the ceiling laugh. (Japanese Proverb)

calculus... [modified]

Anton Afanasyev10-Oct-06 19:27

Anton Afanasyev

10-Oct-06 19:27

i am findisng myself unable to solve the following problem:

An equation of the tangent line to the curve
y=f(x)=x(8 cosx- 2 sinx)
at the point (4pi, f(4pi) is y =???

use pi=3.14(yes, approximate it to that), and ofcourse, cos(4pi) = 1, sin(4pi)=0.

any takers? i cant see why im getting it wrong. yes, this is for homework.

-- modified at 8:52 Wednesday 11th October, 2006

Badger | [badger,badger,badger,badger...]

Edbert P10-Oct-06 19:32

Edbert P

10-Oct-06 19:32

Umm...just pointing out that there is a Math[^] forum and you'd probably be better of getting an answer there.

"A democracy is nothing more than mob rule, where fifty-one percent of the people may take away the rights of the other forty-nine." - Thomas Jefferson

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Edbert
Sydney, Australia

Anton Afanasyev10-Oct-06 19:36

Anton Afanasyev

10-Oct-06 19:36

yeah, but no one posts there. so i would probably get more answers/ideas/nonsense here.

Kastellanos Nikos10-Oct-06 23:19

Kastellanos Nikos

10-Oct-06 23:19

Anton Afanasyev wrote:
yeah, but no one posts there. so i would probably get more answers/ideas/nonsense here.

Here you will get only 2-3 anwsers. How to know who is correct if they are not compatible?
Try sent emails to, say, 100.000 people. The most popular answer has to be the correct one.

peterchen10-Oct-06 21:33

peterchen

10-Oct-06 21:33

He still has a better chance for an answer here, but the Math forum would give him less abuse and better karma.

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Vikram A Punathambekar10-Oct-06 21:46

Vikram A Punathambekar

10-Oct-06 21:46

peterchen wrote:
He still has a better chance for an answer here

Might as well open up the Lounge to programming questions then. Suspicious | :suss:

Cheers,
Vikram.

"whoever I am, I'm not other people" - Corinna John.

Anton Afanasyev10-Oct-06 22:09

Anton Afanasyev

10-Oct-06 22:09

peterchen wrote:
but the Math forum would give him less abuse and better karma.

whoa whoa whoa. you mean the votes actually do something? like, make me Rise and Fall amongst the ranks of all the CPians?

peterchen11-Oct-06 2:41

peterchen

11-Oct-06 2:41

Yes, at the end of the universe, The Great Maunder will count your fives and ones and theywill determine whether you come back as hamster. Or badger.

Ed.Poore12-Oct-06 8:43

Ed.Poore

12-Oct-06 8:43

Ah, but which one is better? Surely the most dedicated of CP members would like to give back something to CP (in the form of pedal power).

If you're stuck in a rut:
1) Consult the documentation*
2) Google it
3) Ask a sensible question
4) Try an ancient ritualistic knowledge summoning ( Badger | [badger,badger,badger,badger...]

) dance

5) Phone

* - If the documentation is MSDN > 6.0 then forget it!

peterchen12-Oct-06 9:00

peterchen

12-Oct-06 9:00

As you know, hamster run the servers (more responsibility, but then, Dave comes whipping you about daily), whereas badgers only run the signatures of.. some... members........ Smile | :)

Ed.Poore12-Oct-06 9:16

Ed.Poore

12-Oct-06 9:16

If you're stuck in a rut:
1) Consult the documentation*
2) Google it
3) Ask a sensible question
4) Try an ancient ritualistic knowledge summoning ( Badger | [badger,badger,badger,badger...]

) dance

5) Phone

* - If the documentation is MSDN > 6.0 then forget it!