[REL] SH4 v1.3 Real Navigation Mod

[Mav87th]

With permision from Kaleun Freddie and Vanjast i have compiled a mod for Real Navigation for SH4.

It is similar to the mod for SH3, but with differencies.
The differencies being that its based on my Menuxxxxxxx.ini file and that i have modded the camera- and scenefiles to be as close to real as possible.


First the visibility has been increased to about 20km with a Horizon setting of 2300 upped from the default 1000 that gives 8km. This first of all enables you to track ships over the horizon from the masts and funnels, but allso puts the horizon at the correct "level" for SR and SS measurements.

Secondly the periscope, binocular and TBT angular angles has been fixed to you can measure correct altitudes of fx. landmass with the scope. I dont know how accurate the landmass altitudes are, but IF its somewhat precise you can plot from land sightings now non the less.

Thired I have deminished the sunsize to the real live angular size of 0,5° - so it will be a lot smaller then your used to. Same value goes for the moon as it shares angular size with the sun.

Fourth I have allso made a new sextant image that pops up with the stopwatch, and is draggable with it. To me this works just fine as im used to use the stopwatch anyway when taking sun rises/sets.

I have included all the documentation that has helped me to figure out how to do this incredebly complicated way of navigating - im sure glad i live in the age of GPS... :arrgh!:

Best Regards
Martin "Mav" Vinther

It can be downloaded here:

http://files.filefront.com/SH4+v13+Real+Navigation+drar/;8173917;;/fileinfo.html


ps. I can not respond to questions the next week or so due to vacation, so please be patient.

[sqk7744]

Mav87th (http://www.subsim.com/radioroom/member.php?u=214194)Very Cool!

downloading now :up:

[CaptainCox]

YEY! Way cool. you actually see the smoke stacks????
Could you post the tweaks, cause I need to do this manually. Please!
:up:

[Mav87th]

CaptainCox i guess you meen the fixes to the scene.dat file only right?

If so you need to alter the tweek file by appending the green lines shown here:

........snip
absolute,color,1A21,TailColor
absolute,single,1A33,TailAlpha

[32]
DropDownName=Lightning
absolute,single,1B56,Height
absolute,single,1B6A,MinDistance
absolute,single,1B7E,MaxDistance
absolute,single,1B8E,MinTime
absolute,single,1B9E,MaxTime

[33]
DropDownName=Horizon
search,Camera,1,Single,+11,ZMax

END of the scene.dat tweekfile

Then you open Scene.dat via the Tweeker tool and make the setting for the Horizon to be 2500 - voila 20km visibility.

Mind i said i could see the stacks - not the smoke it self.....

[CaptainCox]

Cheers man. Will have a look when i wake up properly here (DARN CATS!, hungry and its only 5 AM, back to bed):dead:

[Uber Gruber]

Brilliant Mav...and about time too, what took you ? :arrgh!:

:up::up::up:

[ICApproval]

Plot Course question

When I load this mod I can no longer plot a course. Am I doing something wrong? I must be!

Mark

[leovampire]

this is about manual navagation if you read the read me's for the mod you will see information about what it changes in your game for you to use this properly. Very complicated yes but if you want real life navigation for the 40's before GPS this is the way to go.

Just another way to add more realism to the game for the people who want it.

It teaches you in the read me's how to plot corses and know where you are by using the sexton and maping out everything in the sky to figure out possition and course.

Good luck!! I tryed to do it just couldn't get the hang of it. Good for people who have tryed and was able to sail this way in real life.

[ICApproval]

Thanks so much for this clarification - makes sense now.

I do love the revised periscope features for view and magnification. Any way to make just these changes?

[leovampire]

I will go back over the data in a while and see what can be done and get back to you on it just have to check some stuff for our mod release so give me some time then I will get info to you unless someone wants to help you before then.

[WernerSobe]

i wonder when a manual cooking and manual cleaning up the toilet mod is going to be released. Seriously, what is the navigator good for? A captain is not supposed to track the location of the sub.

I appretiate your work but i have no desire for manual navigation, since im playing captains role and have to concentrate on captains tasks not on the crews. I try to do that in every aspect. I never fire the deckgun on my own and only use sonar and radar stations when it is realy unavoidable due to missing tasks of AI crew.


Now about navigation. I remember another game called "B17 the mighty eight". It was pretty much the same as silent hunter but in a B17 bomber. You ware managing the crew, meeting decisions and if you wanted you could switch to any crew members seat and drop the bombs, shoot at bandits or - navigate...

So why did i mentioned that? The navigation in that game was incredibaly cool. There was a map view simmilar to the one in silent hunter. But it wasnt a godeye. Everything on the map was put in there by the crew and the crew wasnt perfect. The navigator was trying to couple the position of yourself and everything around by looking outside at cities, coasts, roads etc. When there was nothing to see he tried to couple using speed, heading and known wind. But after a while he was totaly lost and your plane was not necessery where it was shown on the map. But the navigator was telling you when he was not sure about present position or when he was totaly lost. In that case you could go to the nav map and drag your plane on it to where you think you should be, or you could look outside yourself and try to find a reference point. That is how real visual navigation work and it was very good in that game. You could never be sure if your position on the map was where you realy were, and you often came out of a cloud cover and found yourself somewhere else and could even here the navigator cursing :-)

Of course there are no referation points that can be used in a sub. Seamen use the sun, stars and the clock. But the same idea would realy improve the game. Making the navigation vulnurable to errors. So the navigator would update the location every few hours and when the visibility condition didnt let him, your position would be flawed or postponed until he can see the sun or the stars again.

That would kickass but you know it is not possible because it goes to deep into game mechanics. Anyway, so far ill stick with GPS mode.

have a nice day.

[don1reed]

Good post, Werner.

I'm one of those old guys that still enjoys celestial navigation. It's something I still love to do in real life. Why? Well, it's become a lost art from the Naval Academys point of view anyway, as most have relagated their sextants to the museums and archives...eBay...(heck of a way to treat a scientific instrument)...and opted for new, modern, GPS systems. There's nothing wrong with that concept amoung peaceful nations.

...but, in the event...(may the maker prevent)... some future nuclear mishap causing a major elelctro-magnetic interruption, the human race may need a "fall-back" line of defense, such as typewriters, sliderules, sextants, and radios with tubes instead of transistors and ICs..and where will the souls be, the next generation, who'll know how to use them ?

I like the option of being able to choose this RealNav mod just to keep alive the knowledge of the past, the skills needed to get from point A to point B...although, I will admit...the rendition of the sextant in the mod is no where near as accurate as what a real sextant would be able to provide.

The USNaval Academy's standard of accuracy, when cel nav was still being taught there, was 0.5 moa or (1/2 nautical mile) (1000 yards).

Hopefully, a new generation of players will see this mod and it will peak their curiosity to do further research into the whole realm of navigation, mathematics, and science in general.
:up:




As passengers on space-ship earth, we don't have much say

[Uber Gruber]

I'm one of those players who was/is attracted to the whole idea of manual navigation and watched the accompanying threads with great interest. Even bought a book or two on Astronomy and another on the history of Longditude (exciting book) but sadly I still can't get my head around what I have to do in the game.

I think its because I lack some basic understanding of celestial navigation. I'm quite good at maths so i think its a conceptual thing. I read all the read mes with the mod but still just can't get the hang of it :-( I found they assumed us beginners had a certain level of knowledge which I unfortunately dont have :doh:

Can anyone reccomend a resource for the absolute beginner to start with ?

Cheers...

[don1reed]

Hi UG.

I think what a lot of folks don't see from the git-go, is that one cel nav observation only provides us a Line Of Position (LOP). After we take several cel nav sights spaced apart by several hours during daylight (sun), then we can advance our first LOP to our most recent sun sight based on the distance we travelled since taking the first sight, (called a running-fix), and usually (if we did everything right), the two LOPs intersect. Its at the point of intersection where we then construct (pencil & straightedge & protractor) our true heading and position on the chart.

Usually, sailors do this in the morning, noon, & evening.

At night, they use stars, planets, moon. Whats different at night (evening/morning twilight accually) of course is that its possible to get three or more heavenly bodies during one sighting. (spaced about 120° apart) This provides a FIX. No need to do a running-fix as with the sun alone.

Sometimes during daylight its possible to observe sun and moon fix, this also eliminates having to do a running-fix.

...and thats the short 'n long of it.

...oh...one more thing...just like shooting torps at a target...the closer that two LOPs are to 90° intersection, the more accurate the fix.

[JimRat]

Basically when you are taking sights of Celestial objects with a Sextant you are measuring the "height" of the object above the horizon, measured in degrees. The distance for the base of the Trigonometric Formula is assumed to be the Observer's horizon, (based on their height of eye above the surface of the Earth / Sea, i.e. Sea Level). When you apply this measurement to a world chart, (not that you need to, but for illustrative purposes), you would get a circle plot that would show everywhere on the globe that the observed object would be at that height. Now if you were to observe several objects at roughtly the same time then you would end up with several global circles plotted, however there would be only one place on the globe where all the circles would intersect. That is really what is going on when you use Celestial Objects for Navigation. There are several factors that can upset the accuracy of your observations; indistinct horizon (i.e. Haze), inaccurate time measurements, (this is why Celestial Navigation at sea was not very accurate until the late 18th Century), and misidentification of the Celestial body observed, (there are roughly 52 stars used for navigation plus the Sun, Moon, and 5 inner planets, of course not all 52 stars and/or 5 planets are available at any one time).

In the morning and evening normally 7 stars and/or planets would be observed, cloud cover permitting. This would be done during the time known as Nautical Twilight, (roughly 30 minutes before Sunrise and 30 minutes after Sunset). When observing morning and evening stars as it is called, you must advance or retard the resulting LOPs to a common time, (as you can observe only one object at a time). The usual method is determining a mean time between the first observation and the last and applying the ship's coure and speed to each observation for neccesary amounts of time to reach the "mean time" of observation. This should result in a fairly tight intersection of the LOPs generated. Also if you observe the Sun as it is rising or setting the resulting LOP, (Line Of Postion), would be a Longitude line. While if you observe the Sun at LAN, (Local Apparent Noon), then the LOP is a Latitude line.

As don1reed stated during the daylight hours the moorning Sun Line would be advanced to the Noon Sun Line based upon the vessel's course and speed during the intervening hours, and then again both lines could be advanced to the afternoon sight. The inaccuracies can creep in based upon multiple course and/or speed changes and bad record keeping of the same. The biggest factor that can mess up your sights though is a bad Time Reference, this is why most vessels used to keep at least two Chronometers onboard to compare against each other to track GMT, (or Zulu time in the military). These would be compared against a time signal received by the vessel via radio each morning and a log kept on each Chronometer as to how far ahead or behind it is of GMT and whether it is gaining or losing time.

Another thing, (at least in the Northern Hemishpere), at night one can take a sight of Polaris, (North Star), anytime the view of the horizon permits, to obtain a Latitude LOP. This however is not possible in the Southern Hemisphere as there is no "South Star" available for such a sight.

Now the resulting Arithematic to reduce the observations to LOPs is very complicated if one were to do them by hand, however the formulas have been greatly reduced, (i.e. simplified to basic math), by using Sight Reduction Tables that I assume are published by many governments around the world, and here in the USA by the US Naval Observatory, coupled with the use of the Nautical Almanac published by several sources, (USNO, UKRNO, etc.).

I hope this has been helpful to those of you new to the idea of Celestial Navigation, however please remember that accuracy in this area of Navigation usually takes many Years of practice, (which is why competant Ship's Navigators used to be so prized in the Merchant Marine and in the Naval Services around the world).

JimRat, (former Quartermaster Second Class USNR):up:

[don1reed]

Hey, Jim, nice post...

and welcome to the "Rat" race.:lol:

[Frederf]

Can't wait to have a big stinkin' notebook full of sightings. And while someone mentioned that this is the Nav officer's job, well...

1. I want a taste of all the duties on the boat.
2. It's fun/challenging
3. The nav officer is way too good.

Thanks!

[Bill Nichols]

Now all we need is a version of this that is compatible with the 'Reflections on the Water' environment mod.

:up:

[tater]

^ yes.

[leovampire]

scene file and add ROW ontop of his work and totaly preserve his stuff guys if you want me to do it!

I tryed and got no reply so maybe if you guys ask him?

[tater]

The big change seems to be the sun/moon radius figures, he's got 2300 and stock scaling.

tater

[leovampire]

check the read me files and he explains it all.

[Munchausen]

1. The earth rotates and, as it rotates, the sun appears to rise and set.

2. The earth is tilted so as to not be perpendicular to the sun. Ergo, the sun rises and sets at a different time each day ... these times can be found in a set of Tables.

By JimRat: ...Arithematic to reduce the observations to LOPs is very complicated if one were to do them by hand, however the formulas have been greatly reduced, (i.e. simplified to basic math), by using Sight Reduction Tables....
3. You can build your own set of Tables by making use of the following website:

http://aa.usno.navy.mil/data/docs/RS_OneYear.php

4. The primary reference point for sunrise and sunset is Greenwich, England. All times found in the Tables should be referenced to Greenwich time ... also known as “GMT” or “Zulu” time (e.g. “1525 Z” denotes 3:25 pm Zulu time).

5. In Silent Hunter IV, the motions of neither the sun nor the moon correspond to the real life Tables. So far, I've observed errors of more than 30 minutes between computed sunrise and in-game sunrise.

Note: Thankfully, the phases of the moon are fairly accurate.

6. If anyone can direct me to a set of Tables that corresponds to when the sun and moon rise and set in the game, I’d be most appreciative.

[Bill Nichols]

Can't wait to have a big stinkin' notebook full of sightings. And while someone mentioned that this is the Nav officer's job, well...

1. I want a taste of all the duties on the boat.
...



For your first duty you have a choice:

a) chipping paint
b) mess crankin'

[Frederf]

I've given celestial navigation here a try in game. Oddly with this mod my sun was still about 1° or larger which confused me. Perhaps I shouldn't have tried to JGSME it? I was very excited to try and spent a couple days setting it up. I read more than my brain has taken in since graduation as well.

I did not try any LOP or sight reductions due to my unfamilliarity and my lack of reference material. I thought I'd learn to crawl before I could beat Jessie Owens. The following is my impressions and creative spark on the subject.

Latitude by Sun or Polaris:

Once I got an actual value for when to take the sun shot at noon (the time to the minute) the better I did. I knew my position and looked to see if the expected cel. bodies were where they were supposed to be when they were supposed to be there. My verdict on the sextant... brilliant idea, just plain not accurate enough. I had ambiguity of 1-2° with the big sun which I might be able to get down to 0.5° with a lot of practice, 30nm. Not the best. I also found it very hard to take most of my shots whci were very high overhead 60°+

During the day I was lucky to get partial cloud cover. This reduced the sun from a huge blinding glare ball to an actual circle to get a measurement. I don't know how good any of these shots were because I was running 1280x1024 (a very common but unsupported resolution by this mod) and 1280x960 to try and weed out the possibility of error.

Polaris is hard to find for me. Video game stars (Silent Hunter, OFP/ArmA) are harder than real life for some reason. Knowing it was directly north and between 1° and 5° above the horizon helped me find it (latitude 3°). Freezing the game with the sextant bottom on the horizon helped quite a bit as did finding a game station that was view stabilized like the flak or deck gun.

When I was 1° S lat. I had pretty much no idea how to take a measurement. I heard there's some method of using a Orion belt star at it's maximum altitude as a 90-L measure but didn't attempt it.

Longitude by SR/SS:

The SS times to the upper limb of the sun via this program I got were brilliantly right on. Plug in my known position (sent a patrol report), the date, and the SS time was right on. The SR time however was 2 minutes too late consistently. By the time the calculated SR time came around the sun was always exactly 1/2 way out of the water.

If I could find a source with SECONDS I could probably get very acurate longitudes, ironically much better than my sun latitudes. The chronometer is by far more accurate than the sextant in this regard. Of course I compared calculated times based on a known position (down to the minute) and not the usual finding position based on times. I figure I'd only be a minute of time off, so 4nm which is acceptable for me.

Conclusions:

1. Sun glare is killer. To create reasonable sun measurements a filter needs to happen or just to turn off the glare altogether.

2. Create a stable, dedicated sextant platform. A special clickable zone of the conning tower that had no-rocking-with-the-sea, any FOV you want (45°?) to have better readings.

3. Verify sun and moon size. This is probably just my failure to read install instructions or read angular size but I swore that the sun was not the proper 0.5°.

4. Look into a "deckgun" sextant. Try pointing the deckgun at a point above the horizon, then hit tab or zoom. Notice how the range number is based upon elevation and is very sensitive. If someone could do the same kind of coupled number-elevation for a "sextant gun" than sextant readings would go from +/-0.5° to +/-0.1° or better.

I'm still interested in this idea, just wary of how practical it is as the mod and game stand now.

[Munchausen]

Polaris is hard to find for me.

The easiest way to find Polaris is to use the Big Dipper (Ursa Major). The following PDF file illustrates:

http://www.fvastro.org/beginners/beginner-part1.pdf

Notice how the front edge of the "dipper" points directly to Polaris. If you'd like a complete sky chart, try this one:

http://observe.phy.sfasu.edu/SFAStarCharts/SFAStarChartsAll.pdf

The SR time however was 2 minutes too late consistently. By the time the calculated SR time came around the sun was always exactly 1/2 way out of the water.


The halfway point is suspect ... interior lighting always switches from night (red or blue) to day when the sun reaches its halfway point ... and switches back at the same halfway point during sunset.

I assume you're using the sun tables that came with the mod. If so, what specific corrections are you making to adjust for your current position?

[Frederf]

Using the big dipper is no good as I was at 3°N and 1°S latitude respectively, the big dipper was through a couple billion tons of rock and slgihtly hard to see. Again this is a small matter that simple practice and star charts can easily remedy, not worried at all.

Actually my SR/SS times came from Almanac 1.0 by Stephen R. Schmitt, 2002 but I checked them across to the tables that came with the mod and seem very close. I'll do a direct comparison (since I inputted a weird lat/long that's not on the table).

20N Mar21 1943
Table: SR 0604, SS 1810
Almanac1.0: SR 0604, SS 1811

30N Jun4 1939
Table: SR 0431, SS 1924
Almanac1.0: SR 0432, SS 1924

So it looks like the table is from the same data (perhaps the same program, pre 1950 being hard to get) and the table simply averages over 1939 to 1945 while the program does not. Another thing I noticed is that setting the time zone to anything other than +0 Z in the settings gives confusing results. It seems to say "The local time in time zone X will be _____ when the sun is rising in time zone Z." which may be right but is entirely unhelpful. The local time that the sun rises in each time zone on any given day of the year should not be more than 10 seconds or so different.

I've also found that the calculated sunrise, the upper limb rise, the center body rise, and the red light switch happen at 4 seperate times. This notion of "The red light goes off when the sun is half way out of the water" doesn't hold true in my experience. Instead the red light tends to go off a few minutes after half-sun.

More testing ist reqwuiret.

[Munchausen]

Using the big dipper is no good as I was at 3°N and 1°S latitude respectively, the big dipper was through a couple billion tons of rock and slgihtly hard to see.

Polaris is usually used when you want to determine your latitude (assuming you're in the northern hemisphere) and, consequently, you need not wait until sunrise or sunset to take a sighting. Depending on the time of year, Ursa Major will eventually rotate around to where you can use to it find Polaris. Granted, star shots were usually made at twilight so, if the Dipper isn't around when you need it, try using Cassiopeia (shaped like a quirky letter "W" with the center spike pointing toward Polaris).

Another thing I noticed is that setting the time zone to anything other than +0 Z in the settings gives confusing results. It seems to say "The local time in time zone X will be _____ when the sun is rising in time zone Z." which may be right but is entirely unhelpful. The local time that the sun rises in each time zone on any given day of the year should not be more than 10 seconds or so different.

This is really the problem. "Base Time" is not really defined. If the watch was set to GMT, it would probably confuse most players (having the sun rise at midnight would draw far too many complaints). As it stands, it's almost impossible to determine if the error is in latitude or GMT.

For example, for a D.R. of 12*15' S 115*00' E, on 26 Jun 42, I calculated sunset to be somewhere around 1745 Z. If I were to then use Fremantle as my "Base" time, correction for longitude would move sunset to 1744 "Z" ... not exactly GMT. If I did use GMT, at 4 minutes of time per 1 degree of longitude, that would be about a 7 hour 40 minute "correction."

I've also found that the calculated sunrise, the upper limb rise, the center body rise, and the red light switch happen at 4 seperate times. This notion of "The red light goes off when the sun is half way out of the water" doesn't hold true in my experience. Instead the red light tends to go off a few minutes after half-sun.

Probably because you've changed the size of your sun (or not). I left my sun at default and the switchover is consistent ... midway between one limb and the other. Or, timewise, 10 mintues ... 20 minutes to fully rise or set. The moon, on the other hand, only takes 14 minutes (thereabouts ... I haven't had a full moon yet to make certain).

Btw, compared to the above D.R. calculation, my actual present position at "sunset" was 12*35' S 114*55'E ... and the sun actually set at 1900 ... 111 minutes late.

[gutted]

extremely interested in all of this.. but it seems like there may be too many problems with it.

hope someone can sort it out and give a good tutorial for the navigation beginner.

[Frederf]

I kinda have to complain that this "real nav" mod removed all the fine lines on the map for lat/long. This makes plotting your position, once calculated a real pain! I can still zoom in the same amount but now there's just blank ocean-blue paper there.

Polaris is fine, in face the W constellation is easier for me to find more often than Ursa major/minor. The base time should be defined as the local time in the center of the time zone that your base is in. Basically if your base is in San Francisco your base time is GMT-8. Other huge SS/SR time differences during some of my tests are probably due to other factors besides this. I find base time a no-brainer.

Further tests show that the red light goes on/off at mid-sun.


Can I ask what people have been doing for accurate latitude shots that exceed the rather rough judgement of the altitude of the sun using the sextant? Also using sun for latitude is not a simple 90-A = L arrangement but involves what day of the rear it is. Can anyone post details about that correction?

[Munchausen]

I kinda have to complain that this "real nav" mod removed all the fine lines on the map for lat/long. This makes plotting your position, once calculated a real pain! I can still zoom in the same amount but now there's just blank ocean-blue paper there.

I didn't install the mod ... I just try to use sun and moon tables to determine when to surface and when to remain submerged. So I didn't realize this was part of the mod. In fact, the navigation chart should have more, not fewer, lines. I suspect the lines were removed to keep the player from "cheating" ... but it's hard to plot a D.R. or fix without latitude, longitude and tic (incremental marks along lat/long) lines.

The base time should be defined as the local time in the center of the time zone that your base is in. Basically if your base is in San Francisco your base time is GMT-8.

My base (point of departure) was Fremantle. Although sunset is later than I'd expect using the Tables, it comes nowhere near what I'd get if I used GMT +/- Fremantle's time zone.

Also using sun for latitude is not a simple 90-A = L arrangement but involves what day of the rear it is. Can anyone post details about that correction?

Thanks to the tilt of the earth, the sun doesn't "top out" at the same height above the horizon every day of the year. The sun reaches its highest point ("topping out") at what's called Transit ... and you can build a table for transit times in much the same way as you build a table for rise and set times.

Example:

It's the 4th of July and you want to find your latitude by taking a "noon" sun shot. Using the sextant, you track the sun and find that it tops out around 1204 local time, at 82 degrees ... to the north.

Transit tables show that, at latitude 30* north, the transit altitude of the sun is 83 degrees on the 4th ... but the sun is south of the observer. So ... you've got the wrong table.

At latitude 20* north, transit time is 87N (the sun is now north of the observer ... so, somewhere in between 30* north and 20* north, the sun was directly overhead ... if you were to sail quickly from 30* to 20* you'd watch the sun pass from south to overhead to north of you).

At latitude 10* north, transit time is 77N.

Interpolating, transit time for 82N would be latitude 15* north. This would be your present postion.

[Frederf]

It should be a simple fix to slog into the SH4 nav mod and ... ya know.. make one that makes sense in terms of how detailed the chart is in lat/long lines. They do state something about cheating prevention as reason for some map changes. I thought the intial zoom level change was sufficient. Invisible forest, beautiful trees.

I was trying to plot a fix when I realized that a degree wasn't 60nm wide... not even close. I tried interpolating like "My longitude is 55.487% between 150°E and 160°E so do the math. It's 67.8nm between so it's 33nm east of.. blah blah math.

My base (point of departure) was Fremantle. Although sunset is later than I'd expect using the Tables, it comes nowhere near what I'd get if I used GMT +/- Fremantle's time zone.

I did this too. Once for Midway, once for somewhere else. In Midway the SS/SR times were really close, in the other place they were way off. I don't know if it's the Base Time / GMT difference necessarily that is making these times wrong. The Base Time might work as it should but there might be some other aspect of the game that is causing the times to be off.

On the other hand, I am still suspicious that Base Time might be a weird time zone like GMT+9.74345 because it's 15*9.74345° west of Grenwich for example.

The sun reaches its highest point ("topping out") at what's called Transit ... and you can build a table for transit times in much the same way as you build a table for rise and set times.

So a table is required? I could build such a table but no such table came with the mod in the hodgepoge of .pdfs and .docs. Also while I have your attention, there is this definition of transit or altitude that gets thrown around quite often and even through a few hundred pages of reading I can't get anyone to really explain it before talking about oblate spheroid this and equation of time that.

A transit of the sun is:
1. Not neccesarily at 12:00 local +/- 20 min or more.
2. Happens when the Sun is at the highest elevation
3. Happens when the sun crosses directly 000/180 true (also known as crossing the meridian)

Correct?

And how accurately are you measuring altitudes with the sextant? To the 0.3°?

[don1reed]

Hi all. I've got to hand it to the modders for attempting this, but really, the sextant here is no where as accurate as a real instrument is in real life (RL). It doesn't even come close.

As I mentioned in earlier posts, the USN Academy's standard for sextant accuracy was 0.5° when they still taught cel nav there.

The sextant in the mod is and always has been a modified "straight-edge ruler". The nearest thing to a real sextant and it's workings is in the virtual sailor sim (vs7). It has adjustable shades and magnification, but it too has problems with celestial objects being out of sync with reality. It's the finest the market has come up with to date.

One day, I'm sure, it will happen that the Dev's or Modders will succeed in presenting that aspect of real life.


edit:

just think of it...the sphere of the stars, planets, moon, and sun are all rendered on separate transparent, rotating spheres that must be in sync with the date, time, and season to become anything resembling proper celestial ephemeris to begin with, then a working, scientific instrument, as a sextant is, must be also rendered to be able to measure the actual body's correct altitude...no matter where on the globe the vessel happens to be...it'll be some undertaking, I'm sure.

Hand salute to those that will get it done.

btw: transit is when the body leaves Ante Meridian to Post Meridian (AM to PM).

cheers,
cheers,

Cheers,

[Munchausen]

Well, you can always download and install Orbiter at:

http://orbit.medphys.ucl.ac.uk/orbit.html

then use the HUD to measure altitude of celestial bodies.

A transit of the sun is:
1. Not neccesarily at 12:00 local +/- 20 min or more.
The earth never does anything exactly like it should. Trust the tables.
2. Happens when the Sun is at the highest elevation
... at your present position for that specific day of the year.
3. Happens when the sun crosses directly 000/180 true (also known as crossing the meridian)
For that same 4th of July example, azimuth of the sun during transit was ... er, my tables don't say (ask me about azimuth during sunrise and sunset). Ergo, I would assume the sun will be either due north or due south at transit time (maybe later I'll check an old Air Almanac and see if I can confirm that assumption).

And how accurately are you measuring altitudes with the sextant? To the 0.3°?

I don't use the sextant. If I want to measure altitudes, I use the tic marks on the periscope (at low resolution). It doesn't help much with navigation but it does give me a "heads up" for how long I'll need to wait for sun/moon set.

[Notewire]

Guys,

I used this one and it crashed my computer - I have ROW, RFB, and RSDRC loaded.

Is this RFB compatible?

Also - even if I can't get the sextant, I couldn't get the GPS dot off my NAV map, I think it has to do with the fact that the blank location files in this MOD are TGA files, and SH4 (unlike SH3) calls for DDS files. Anyway, any help would be greatly appreciated - does anybody have a UnitSUB DDS file?

Thanks in advance for the help,
Yarre Notewire