Real Navigation Mod

[don1reed]

Hadrys,

Do you have a mod that puts those crisp LAT LONG lines on SH3 Chart?

-...-

Make sure before you buy that KM sextant that you have a professional optics man check it over. The pro will be able to tell if its been dropped or out of serious alignment.

If its in good shape your accuracy at sea should be within 0.1 m.o.a. if the mfg was CASSENS & PLATH or Freiburger.

edit: btw, if any of you gentlemen have a current or old Nautical Almanac lying about, the SR/SS LAN tables on the righthand pages don't change from year to year and can be used.

Best of Luck,

Originally Posted by don1reed

Hadrys,

Do you have a mod that puts those crisp LAT LONG lines on SH3 Chart?

Make sure before you buy that KM sextant that you have a professional optics man check it over. The pro will be able to tell if its been dropped or out of serious alignment.

Nope cause I don't understand this RAW format... either way it's useless now. I suppose that we should forget about getting proper longitudes.

About KM stuff - I have lot's of time to collect those few desired items, build that 100+ cm VIIc model with brass details, dive deeper, go further etc but thx for the tip! I'll sure do that.

[ichso]

That's a real pity. I was so looking forward to finally test this mod on my own. I will do it anyways and see where I get with it

[ronbrewer]

I haven't installed the RealNav mod yet since I haven't come back from my current patrol. However, I'm planning on it sometime this week. I'm curious about the longitude issues. Reading through the threads it looks like the problem is encountered when east of GMT. If that is the case do you think the results will be better for patrols that start from the west coast of France (fall '41 and beyond)?

[don1reed]

Longitude:

Even without the aid of Celestial Navigation, the player can still navigate using Dead Reckoning to get to an Assumed Position within the sim, i.e., Distance in Nautical Miles = (Speed in knots x Time in minutes) / 60.

Make yourself a UT to Local Time Zone converter with whatever spreadsheet pgm you have. Its not hard to do. (Google: Time Zone Chart)

Van's Sun Almanac will work for SR & SS. These occurrances are based on when the sun is in the center of a time zone:

0-15-30-45-60-75-90-105-120-135-150-165-180 E/W. Each time zone is 15° wide, 7° 30' on each side of center.

You have to do the rudimentary simple math of adding or subtracting the time of SR or SS at your location from the center of the time zone of your assumed position based on van's sun almanac. If you're further west of the center of your assumed Time Zone, naturally, your SR or SS will be later. Depending if you are E or W of prime meridian and which side of time zone center determines whether you add or subtract.

You can also use the Sun Almanac to determine the Local Apparent Noon for the center of each time zone by subtracting SR from SS time, then divide the remainder in half, then add that half to SR to find LAN...then again, the rudimentary math as above.
When the sun is due N or S of your location, its noon.

In short, my advise is not to give up too soon on the mod. It needs a lot more eyes and players to do the testing.

Best of luck,

[ichso]

As I am still on patrol and want to install the mod after finishing it, I tested just a very little bit yet
I measured how far WEST I am from Greenwich (1625km, so drawed a 270° line from there) and what the difference of local time to GMT looks like (exactly 1h). I wanted to do this a little bit more to see by myself how reliable the local time is and if I could use that to get an idea of my current longitude.

Originally Posted by ichso

As I am still on patrol and want to install the mod after finishing it, I tested just a very little bit yet
I measured how far WEST I am from Greenwich (1625km, so drawed a 270° line from there) and what the difference of local time to GMT looks like (exactly 1h). I wanted to do this a little bit more to see by myself how reliable the local time is and if I could use that to get an idea of my current longitude.

longitude (in km, per 1°) = (111.320 + 0.373sin²φ)cosφ where φ is latitude



source: wiki

[ichso]

So where is the problem about getting longitude then ?

[XLjedi]

The idea of real navigation certainly sounds interesting...

I'll have to read this thread thru in a little more detail. I guess the nagging issue I have in the back of my head is the fact that the game map is a distorted... how shall I say... pre-Columbus (i.e. flat world) map.

Does that not confound the trig? I would suspect dead-reckoning would be prone to very little great circle-type error.

Forgive me if it's already been addressed, I'll go back and read now...

[ichso]

If I understand you correctly, then it has already been dealt with by:

longitude (in km, per 1°) = (111.320 + 0.373sin²φ)cosφ where φ is latitude

The determination of the latitude says something about the angle in which the map should be "round" at a certain latitude value. The curvature of the world at this latitude.

Originally Posted by ichso

If I understand you correctly, then it has already been dealt with by:

The determination of the latitude says something about the angle in which the map should be "round" at a certain latitude value. The curvature of the world at this latitude.

The map is OK, it's a proper projection on flat screen. If you connect some points, they are exactly on a given meridian as they should, but the whole map should be about 50% width! The explanation why is in post #15 and the above formula.

I've got Vans reply, he's currently busy but still in the subject. Didn't have a clear mind to go though this yet:

Originally Posted by vanjast

You can still measure longitude, but you must be aware of the following.

- The GMT clock (lower right corner) locks onto to either Greenwich or the nearest Meridian (longitude line) to your position when you load/start a mission. This time remains your time until the next (save)reload/mission. Make allowances for this when reading the Sunrise/Set tables, and you'll find that you will probably get within 1 Degree accuracy.

- The local clock that appears above the GMT clock is only usefull for noting the hourly changes between this and the GMT clock. These hour differences occur at multiples of 7.5 Degrees (not 15 Degrees).
For example:-
Your GMT = 16:00 and your Local = 16:00.
Suddenly your Local = 15:00, which indicates that you're an hour behind GMT (or your last load position).

You're not actually an hour behind at this change but 30 minutes (horrible game bug).
Use these formulae for calculations.

Going West Longitude = 15 x (GMT - Local hours) - 7.5

Going East Longitude = 15 x (GMT - Local hours) + 7.5

[ichso]

Nice, thanks. This should help out. It's a little bit of a way around but that's no problem.

[ichso]

Something that might help:
At the end of my last patrol I tested how much my boat gets off course in bad weather. I hadn't really much time so I did some rudimentary test only.

Wind was coming from 312° by a speed of 15km/h. Excluding visibility it was the worst weather SH3 can produce. Here are my course settings, and how far I travelled and how much my final position differed from the estimated one.

Course 90°
after 10km: ~500m difference to North (so to the left)

Course 0°
after 10km: ~275m diff. to East

Course 180°
after 20km: ~75m diff to East (but more due to a slight error in the initial course setting because it was the same after the 20km's)

Course 270°
after 10km: ~600m diff. to North

Doesn't look quite like I would have expected it, I will redo it more precisely when I have more time for it. This should help set the right course in bad weather conditions so it should reduce the error when "real navigating" :hmm:

Originally Posted by ichso

Doesn't look quite like I would have expected it, I will redo it more precisely when I have more time for it. This should help set the right course in bad weather conditions so it should reduce the error when "real navigating" :hmm:

This is nothing, when transiting for 1000 km in bad weather I have to correct course all the time. Check out with ctrl+click in x1024 how fast the boat gets of the course... I really wonder how I did it for the first time, when my position after several direction changes, was quite accurate in the end (1 screen). Maybe x256 doesn't generate such a big error? All my observations are while doing 7-10 knots. This is a serious problem because small errors on longer distances add up very quickly... it might be realistic but for the gameplay - transit - its very annoying.