Real Navigation with SH4
 

Tests of GMT times versus "Base Time" as the clock is called in SH4 shows, that sun sets and raises look to be just as usable as in SH3 even down to minutes.

The only problem that remains are WHAT TIME ZONE ARE BASE TIME ??? and how does it change over time. I know that it does not change when you save the game (im keeping a logbook and times match whenever i go back into a new saved game)


Below an example:

Game date - 22 november 1942 - located on E 144 deg 50 / N 26 deg 50

I started the stopwatch as the game clock changed minutes, so to have seconds available.

in 3D the sun SET was

Lower Limb - 19:15:00 @ 247 deg True

Center sun - 19:29:10 @ 248 deg True

Upper Limb - 19:40:15 @ 250 deg True


From Almanac data (Starcalc) the real GMT sun SET should be 17:05:00 @ 247 deg True

Difference (to center sun) is + 2 hours 14 minutes or - 16 hours and 36 minutes


3d measurement of Polaris were 310 deg True at 31 deg up from horizon at game Base time 19:57:00

The submarine were parked the same spot the whole time.


Now can anyone tell me what timezone the BaseTime is???

or if this corrosponds with my position lat/lng ?

bump for reads.... this is (potentially) a realism breakthrough waiting to happen

I believe I have a copy of starry night pro, I will give it a shot if you want to make some tests.

todays testing showed, that the starmap is correct as far as to the dates (22. november 1942).

I have now rescaled the SH3 mod's Sextant image and printed it on a transparent, thus enabled a measurement of Polaris for Latitude. And this seems to work fine.

I believe the time is based on Pacific Standard Time however, the dateline issue isn't implemented therefore the clock keeps ticking away at wherever you start off.

I put all data in starry night:

sunset 17:04 @247° (gmt+09:36)
if the game renders the sunset at 19:40, that would be gmt+12:12!

timezone is fubar in sh4

Not necisarily - but the gameclock is just not simple "local time" - i think its based on something els. The trick is to figure out WHAT Base Time is exactly and then just make the calculations from there. It does not matter if you have to say Local time +12 or Base Time +10 - as long as you know that its +10 or whatever it is...

I wouldv'e thought that base time was from the base you departed from.

Showing local time would be my preference same as in SH3 but again crossing the dateline is the issue.

@kv29 you're right!


after some testings I found:

- base time is real local time of the exact position the sub starts
- that means: there are no time zones in SH4 - there is a continuous displacement of time


If You start at W001°00' your "local time" = basetime ist 4 Minutes behind GMT.

So if the clock is ok, time measure should remain accurate for the rest of the mission, or the clock is bad too?

Yes!

And we need the time difference (local time - GMT) for every start - location.

is there any way to mod the "timezone"?
we need an onscreen sextant mod! :oops:

there is a sextant for SH3, but it doesn't work in SH4 - i do my best ;)

http://sh4.wamotec.de/phpBB2/userpix/3_sextant_2_1.jpg

SH3 Sextant: http://www.subsim.com/radioroom/show...eal+navigation


Edit:
@Mav87th
Sorry didn't read your postings completly
YES!


Does the sh3 - sextant work for you?
http://www.subsim.com/radioroom/sh4....extant_2_1.jpg

So when one starts in PEARL one needs use PEARL time - TimeDif = GMT at all times while sailing...

Question is, will this be valid as well if one starts outside the harbor, or will it default to your homebase time there as well.....

http://i77.photobucket.com/albums/j4...eed/Sunset.jpg

Here's an interesting pic of UL sun just dipping beneath the waves. My location: 28-15N 177-32W. What you see is the orange after-glow. The defined circumference of the sun has just disappeared.

Note the time: 18:45. (The interior "RED" light popped on at the same time!)

Well guess what...it seems that base time in SH4 is at the International Date Line, just west of Midway Is. 180°. All other times must then be computed by the player as they make their way across the Pacific.

18:45 btw coincides with my TI-86(Starpath) ephemeris calc/nav pgm., for SS at my posit also. :cool: Don't know if you can see my relative bearing of the sun as he dips, but it's 144° that also coincides with 258° true, the actual azimuth of the setting sun on the RL nav pgm. :)

Scope: #1 aka Observation scope.
Mod: RFB 1.28

Note: reposted from SH3 Mod forum.

@minimax:

You've made the same mistake as I have re sextant mod...

place the bottom of the sextant ( zero 0) on the bottom of the screen, not, I say again---NOT on the horizon. The sextant will not read low angle bodies & make sure the object you are observing is in the center of the screen, that is make sure you are view dead ahead, then press the (-) key to zero the screen. Do not elevate (up/down arrows), just rotate (left/right arrows) to the body of interest...get it centered in the screen. Bring the sextant from the side and maneuver it between the top/bottom of screen, (a small bit of yellow should be seen at top & bottom when properly adjusted. Registration marks). Now read altitude.

As I've requested and said elsewhere, the Observation scope would be a good candidate for substitute sextant, as it can be elevated to 90°; but, we need a way to read the elevation angle from horizon to body.

Minimax - how did you get that Sextant image to be draggable.....


And Don1 -- are you sure its not just course you started in the water west of Midway at campaign mission start... Witch would corrospond with Minimax's opinion about Base Time = time at start position in mission

I got confused :shifty:

I calculated these 3 sunsets:

Pearl Harbor
Date: 07/10/44
157°59w 21°14N
sunset=18:24
SunAlmanac= shows a latitud of 10° at that hour. For 21°, sunset should be at 18:43 :down:
Starry night= visually shows sunset at 18:45

Brisbane
Date: 06/11/42
153°51E 27°9S
sunset=17:12
SunAlmanac=calculating time/degrees between 20° and 30° in SunAlmanac, you get exactly 17:12 :p
Starry night= visually shows sunset at 17:14

Perth
Date: 03/16/43
114°56e 32°11s
sunset=18:44
SunAlmanac=Shows a latitud of aprox 70° at that hour. For 32°, sunset should be at 18:16 :down: :down:
Starry night= visually shows sunset at 18:18


wtf??

@don1reed

Thanx for your explanation - my problem is:


I don't get it draggable!


@kv29
Did you move your sub after starting the game?

I made some tests with the editor:
they're all like that:

******************
start position
40°00' S 140°00' W

sunset almanach:
19.32
sunset on-board-watch
19.32
******************

Same with in- and outside Pear Harbour: GMT sunset = local time sunset


I used that sunset almanac

http://www.vanjast.com/NavMod/RealNav_ReadMe2.zip

published by Vanjast here:

http://www.subsim.com/radioroom/show...eal+navigation

Ooops, Sri, minimax, I misunderstood.
I believe you're correct, however, about the "base time".
I'm making some tests currently to simplify and/or clearify it, i.e, lets say we're based at Pearl Harbor and given a mission to patrol off Honshu and we'll refit at Midway Island both ways.

Pearl Harbor, Oahu, H.I. ZD +10 William.

Midway Islands ZD -11 Love.

Honshu Island ZD -9 Item.

Note 1."Bowditch" tells us to convert Zone Time (ZT) to GMT by adding positive ZT and subtracting negative ZT; conversely converting GMT to ZT, a positive ZD is subtracted, and a negative one added.

Note 2."Bowditch" further tells us re Date Line:

E Longitude----> 180°----> W Longitude = Loose 1 day
1 January 1942--->|---> 31 December 1941
5 July 1944<------|<-----4 July 1944

Even as virtual navigators, we still have to deal with this...so, the first thing we must do before casting off is to calculate GMT.

As we travel westward toward our objective the clock in the sim is still adjusted to "base time", this is the reason sun/rise/set and Local Apparent Noon (LAN) are happening at weird hours of the day and night. In order to compensate, see Note 1. above, we convert GMT to ZT by adding a negative ZD to give us local time at our present location, then we can correctly calculate sunrise/sunset LAN for navigation purposes.

What I've yet to discover is when we refit at Midway Island, does the base time revert to Midway's local time. Anyone know?

Nations have created Standard time/Daylight saving time rules and regs for commercial purposes; but, the sun's place in the heavens obeys no human command.