(REQ) for Cel Nav Scope

[vanjast]

Originally Posted by makman94

so the correct time for taking a measurment is at position 2 ?in other words,the correct placing of scale is on the center ? are you sure about this ?

Definitely.. as that draggable sextant in the SH3 RealNav mod had to be placed in the centre of the screen to be accurate - The same thing for the scope, as the wider FOV resulting from the zoom factor, creates a bigger curve.

One has to have a consistent reference point for consistent accuracy and the centre of the scope is perfect, as it also gives you a bearing reading which is needed for triangulation plotting. Naturally this forces you to make the gradations according to this centre position.

[don1reed]

Speaking as a "User" and not a designer, Vanjast's rendition of 0-60° allows more space between the tick marks, allowing a better judgement of decimal parts.

"Background note": The best made RL sextants are accurate +/- 10 seconds throughout the arc (-5° to +125°).

The only time it will get tricky is when the user is attempting readings on high altitude bodies while operating N of the Shetlands; but, even then, it's not a mission stopper.

[makman94]

Originally Posted by vanjast

Definitely.. as that draggable sextant in the SH3 RealNav mod had to be placed in the centre of the screen to be accurate - The same thing for the scope, as the wider FOV resulting from the zoom factor, creates a bigger curve.

One has to have a consistent reference point for consistent accuracy and the centre of the scope is perfect, as it also gives you a bearing reading which is needed for triangulation plotting. Naturally this forces you to make the gradations according to this centre position.

Originally Posted by don1reed

Speaking as a "User" and not a designer, Vanjast's rendition of 0-60° allows more space between the tick marks, allowing a better judgement of decimal parts.

"Background note": The best made RL sextants are accurate +/- 10 seconds throughout the arc (-5° to +125°).

The only time it will get tricky is when the user is attempting readings on high altitude bodies while operating N of the Shetlands; but, even then, it's not a mission stopper.

hello Vanjast and Don1reed,
thank you for the clarifications
so, a scale till 60 degrees can be usefull in most of the cases ,is this that you are saying ? the scale till 60 degrees is showing at the folowing pic (still have to place some .5 marks ) . what do you think ?

[don1reed]

Very Nice, markman94!

Watching you modders work is always a joy. You guys are truly the glue of Subsim.

[vanjast]

Perfect
You know what you could do.. Is add another (4th) zoom level with magnification 2x (or 5x, 10x) the sextant one. If one centres (vertical and horizontal) the object of observation.. and then turns on the more powerful magnification level, you should get an offset from the centre point that is measurable.

This offset would be the added/subtracted to the original reading to get a more accurate one. Something similar to how a vernier (and sextant) works on the smaller scales.

Now if the sky/star system is this accurate wrt to the map... one should be able to land a torp down Winstons' bath plug.

[don1reed]

@vanjast: check your PM.

Don

[vanjast]

Don.. the SH3 times are wrong with regard to RL.
The problem always has been that ship time and/or Greenwich times are messed up with loading saved games.

The Rise/Set times are usually fairly accurate (within the minute) at the equator, but the error increases as you approach the poles.
This might have something to do with the Mercator projection used for the world map.
What one has to work with is the pole star and the yet to be solved Greenwich (or Base) time.

I have mentioned that someone used triangulation instead of relying on time and Pole star, to get a Fix.
Maybe this is the way to go wrt navigation

[don1reed]

I am currently running a test career out of Kiel, heading N then W out of the Skaggerak, across the North Sea, through the Fair Isle channel, using 60° test sextant, installed in the Attack scope with MaGui F @ 0.9 power, designed by makman94. Date/time: 6.9.1939, using three star fixes taken only from BMNT* and BENT*. So far, the accuracy is within 3 to 10 nm of actual fix.

I have been using the GMT indicated time minus 1 hour.

*BMNT = Before Morning Nautical Twilight
*BENT = Before Evening Nautical Twilight

I am also using the "NAVIGATOR" celnav program for sight reduction.

The method of checking if my fixes are accurate is by saving game, then going to My Documents/SH3/data/cfg/Careers/a/0/a.map

opening a.map going to the bottom of the file to [Waypoints] then separately dividing the two large numbers found behind Pt0 separated with a comma by 120000. Positive dividends = N lat E long. Negative dividends = S lat W long. I then compare these results with those derived by sextant. So far, so good.

I'll keep you informed of my results if you're interested.

[don1reed]

My experiment and experience with the IN-GAME celestial dome, Time, & celestial navigation has failed. But, that's not to say it's a lost cause. I feel certain that within our lifetimes, a programming prodegy will arrive upon the scene and salvage SH3's chart and Time discrepancies. In the mean time, I'll content myself with the lure of CelNav for SH3 with stand alone programs such as Python and Stellarium.

Poseidon has willed that I retreat from this effort for now, but not without leaving an offering for fellow mariners of like interests:
Here is free download with built-in almanac and emphemeris data for Navigation in a TeaCup:

http://mysite.verizon.net/milkyway99/id1.html

A giant Thanks to every Modder in search of HOMOTO.

cheers,

[LemonA]

Originally Posted by don1reed

I am currently running a test career out of Kiel, heading N then W out of the Skaggerak, across the North Sea, through the Fair Isle channel, using 60° test sextant, installed in the Attack scope with MaGui F @ 0.9 power, designed by makman94. Date/time: 6.9.1939, using three star fixes taken only from BMNT* and BENT*. So far, the accuracy is within 3 to 10 nm of actual fix.
...

how can you check your results with the Teacupcelestial navigation program when you do not know the T-Delta value for the data 6.9.1939?
Which t-delta values do you use for 1939ish dates?

[don1reed]

Howdy LemonA

That test ran terribly afoul as soon as I turned onto course 270° upon entering the Skaggerak. But even before that, while proceeding N through the Kattagat from Kiel, to make it work, I had to subtract -1 hour from SH3's displayed GMT time. And things went to the deep six, the longer I kept at it.

The Time in conjunction with the celestial dome in SH3 IS NOT CORRECT Full Stop.

The F5 Chart in SH3 IS NOT CORRECT either. It's simply eye candy for the game mechanics to work. Simple navigation problems, i.e., Speed = Distance / Time, do not work in conjunction with the "chart" as in RL.

By, T-Delta, I'm presuming you mean the difference in UT and TT, (Universal Time vs. Terrestrial Time)? If so, then UT (GMT) is the time that is always on display in the game. When placing the cursor over the displayed time, the TT (Local time) will then be displayed.

The Clocks in SH3, BTW, do not show seconds, and as you and other navigators know, seconds are ESSENTIAL in celnav. The way we've gotten around this oversight by the Devs is to start a hand-held stopwatch just as the perceived minutes change. I play in X1 time compression, anything faster, would, naturally throw my system into the 'head'. But, lacking a hand-held stopwatch, you can obviously use SH3's internal stopwatch and use any time compression you desire. Starting and stopping for fixed-wire speed evaluations caused me to go to an external time piece.

As far as using mods to make the UBoat icon disappear while you attempt to navigate in game, I believe, is putting the horse before the cart. Until certain game functions are repaired it's futile to use a useless chart to guess where you are. Only enemy Destroyers know where I am.

[vanjast]

The pole star (Polaris) is accurate in the SH3 dome wrt to Latitude. The problem has always been the GMT and Ship Time.

Ship Time has been correctly simmed as you pass the Hourly (Longitude) midpoint (so to speak). If you don't know your ship times and methods.. you'll get this wrong.

The problem with Longitude(GMT) and Ship Time comes with the game Reloads - AFAIR they end up being the same time ???

Sunrise/Set times are fairly close to the USNOs almanac according to the 1939-45 time period (within the minute at equator, but losing it at the Higher/Lower Latitudes)
I would say the the game times are calculated at the equator (try a test mission there).. without consideration of latitude.

[don1reed]

Wilco, vanjast. I'll give it a try.

As I mentioned in an earlier post and/or PM, the celestial canopy may be tilted as well, where the ground point of various stars and their inherent circles of equal altitudes are distorted into elliptic ovals instead. This distortion would also cause time and altitude discrepancies. I hope that's not the case.

[don1reed]

True Position: N 0°S x W 0°E, C000 S0 D13 m. Boat type 7b.
Date: 1.X.1939, SH3, Single Missions.
Equipment: MaGui F, with 60° sextant centered on vertical reticule of Attack Scope, (both created by makman94), zeroed on horizon. Time piece: As displayed in game with game stopwatch for seconds.
Height of eye: 1.5 m ASL
True Position per SH3: SH3/Documents/data/cfg/SingleMissions/SM1.map
[Waypoint], Pt0 = 0

Time: 01.01.40 «Schedar Br 350, Ho 32°20’.
Time: 01.02.05 «Capella Br 038, Ho 24°20’.
Time: 01.02.30 «Aldebaran Br 067, Ho 43°50’.

Sight Reduction: Stand alone program, “Navigator”
Calculated position: L 0°8.8’S, l 0°3.9’W
Distance away from true position (c2 = a2 + b2 = 9.6 nm SW of 0°).

Surfaced, Course Change (CC) 270° Speed 8.
Lowered scope to 5.5 m (new height of eye) ASL.

Time: 02.12.50 «Schedar Br 070, Ho 27°55’.
Time: 02.13.09 «Capella Br 119, Ho 34°05’.
Time: 02.13.46 «Procyon Br 175, Ho 18°00’.

Calculated position: L 0°8.0’S, l 0°19.4’W.

True Position SH3: [Waypoint] Pt0 = L 0°0.1’N, l 0°8.5’W.

Time: 05.05.02 ƒMoon Br 016, Ho 39°00’.
Time: 05.05.50 «Alpheratz Br 028, Ho 5°30’.
Time: 05.06.19 «Capella Br 083, Ho 43°30’.

Calculated position: L 0°48.4’S, l 1°15.9’W.

True Position SH3: [Waypoint] Pt0 = L 0°0.3’N, l 0°29.7’W.

-…-

Same three bodies using Python and Stellarium:

Time: 05.05.02 ƒMoon Az 287, Ho 37°39.5’.
Time: 05.05.50 «Alpheratz Az 299, Ho 5°32.2’.
Time: 05.06.19 «Capella Az 353, Ho 43°38.8’.

Calculated position: L 0°6.0’S, l 0°23.9’W.

To illustrate these finding, here is a pic: (Scale: 0.1" = 1 nm)


As you can see, the three fixes using the game clock have me heading far to the SW.

I will try it again and adjust the time until I can simulate the boat's true position and get back with results.

[don1reed]

Ran Single Mission again from N 0°S x W 0°E. Course 000 Speed 0 Depth 13 m. Same equipment as in Post #44. As an aid to my ancient eyes this time, I used a Bausch & Lomb 3x magnifying glass to get a better view of the screen.^^see note below.

Date: 1.X.39

Time: 01.01.07 *Schedar Br 350, Ho 32°20', AP 52.1'
Time: 01.01.42 *Alpheratz Br 325, Ho 53°40', AP 58.2'
Time: 01.02.05 *Markab Br 292, Ho 48°40', Ap 56.7'

Calculated position: Lat 0°16.0'S x Long 0°2.5'E.

I don't like those results. We're starting off on the wrong foot from the gitgo. So, I try it again by adjusting the times slightly with the Navigator program Software:

Time: 01.06.55 *Markab Br 350, Ho 32°20' AP 19.4'
Time: 01.02.55 *Alpheratz Br 325, Ho 53°40', AP 16.5'
Time: 01.02.33 *Schedar Br 292, Ho 48°40', AP 3.7'

Calculated position: Lat 0°00.4'N x Long 0°01.4'E.

These results are much better and reasonable.

Surfaced. CC270° S8.
^^Note: Began using 3x magnifying glass.

Time: 02.23.15 *Markab Br 016, Ho 29°45', AP 17.5'
Time: 02.23.50 *Alpheratz Br 037, Ho 39°35', AP 33.6'
Time: 02.24.20 *Schedar Br 068, Ho 27°00', AP 12.5'

Note: The above times are unaltered game clock times.

Calculated position: Lat 0°1.7'N x Long 0°3.8'W.
True Position:[Waypoint] Pt0=-20107.32, 404.38 = Lat 0°00.2'N x Long 0°10.0'W.

Time: 05.06.05 *Regulus Br 168, Ho 23°20', AP 16.2'
Time: 05.06.39 *Alphard Br 190, Ho 33°30', AP 32.7'
Time: 05.07.01 *Mirfak Br 064, Ho 31°55', AP 41.5'

Calculated position: Lat 0°00.0'S x Long 0°35.9'W.
True Position: [Waypoint] Pt0=-60329.71, 419.41 = Lat 0°00.2'N x Long 0°30.1'W.

Note: The above times are unaltered game clock times.

Full disclosure: In order to get the steadiest possible measurements, I paused the game for each sight as the spacing between each tick mark of the 60° sextant is measured in pixels, therefore the need for a magnifying glass. In RL when single-handed sailing, the skipper/navigator uses a lap-counter stopwatch to gather appropriate data while taking sights.

I'll continue on this cruise and post more data as it accumulates.