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.

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.

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.

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.

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.

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°?

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,

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.

The earth never does anything exactly like it should. Trust the tables.
... at your present position for that specific day of the year.
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).

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.

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