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Old 05-04-12, 04:53 AM   #90
11Bravo
Medic
 
Join Date: Dec 2006
Location: Error Triangle
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The crew of U-13 is enjoying some well deserved leave ashore. BdU is mulling over the results of the first 2 voyages while planning the third.

Now would be a good time to mull over where we have been so we can determine where we should go next.

The goal is in-game celestial navigation. At a minimum that requires working knowledge of how the game handles:

1. Nautical Chart for positions.
2. Time at position and at Greenwich Meridian.
3. Sextant measurement of altitude of heavenly bodies.
4. Almanac Data of those bodies at known assumed positions.

In our previous 2 voyages we have made a dent in all four areas.

1. We used the game editor to explore how lat and lon are actually positions in meters from the intersection of the equator and prime meridian. That knowledge allows one to modify the game map to put in a 1° grid and time zone lines.

2. We used the nautical chart and some rough sunrise/sunset data from almanacs to learn how the clocks behave. One of the clocks seems to track absolute time from a prime meridian. The other clock seems to track relative time within a time zone. Both are offset from Greenwich Mean Time by a base time zone created by starting a mission or campaign.

3. We created an accurate sextant by determining a camera calibration curve to account for how the rendering subsystem displays information on the screen. We learned how to manipulate where the horizon should display on the screen and then measure where it actually does appear, and used that knowledge to determine where a measured star should have appeared.

4. We used an accurate nautical almanac to find the altitudes of stars from an assumed position and compared them to measured altitudes from our actual position. The 3 star fix gave a tight error triangle, but it had to be shifted from the assumed longitude because of the cylindrical map projection for the game.

Each of the topics above required knowing something or assuming something about the other topics first. The reason for that is because that is how celestial navigation works. Your position, the time, and the star positions are all linked together and affect each other. The heavenly bodies are both a clock and a map. We live in a four dimensional world of position and time.

We have the minimum requirements right now for in-game celestial navigation. I have made available for download the minimum tools for doing so and I have openly shared my knowledge of how this works. Anybody could take this and make a cool mod right now and you are free to do so.

But I am going to take the slow boat on this one. I am sure many Kaleuns have an interest in this subject and in the subject of how SH3 works and would like to know more. Most of us are not experts on this but are interested observers. Many of us might not want to do this but are curious how it is done and was done.

BdU has determined they are cautiously optimistic about the results and recommend further testing. In particular they want to see a rigorous testing of the clocks, the timezones, the chart. They want this longitude shift/stretch matter investigated and demonstrated further. They want training materials and documentation developed. And they want another mystery solved. The one about inaccurate sunrise and sunset times in SH3...
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