Learning celestal navigation

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Re: Learning celestal navigation

Postby laukejas » Mon Nov 28, 2011 2:03 am

While experimenting further, I noticed that sometimes, I cannot get a stars fix even with that 41:18 GMT adjustment you suggested.

I'm attaching scenario.
http://www.mediafire.com/?3b8jfha1nv1f270

Position:
39:42:52N
14:30:18E

Time: 02:27:25 (on sextant GMT, uncorrected)
Sighting Sirius. Elevation 27:29:06

Subtracting 41:18 from GMT (GMT becomes 1:46:07), I get my LOP off by 6.4nm
But if I subtract 40:18 (GMT becomes 1:47:07), LOP is off by 0.3nm, which is an almost perfect sight.

Any comment on that, Ron? Can you confirm my results in that scenario?
laukejas
 

Re: Learning celestal navigation

Postby seanpatrick78 » Wed Apr 11, 2012 5:25 pm

Has any progress been made on this issue?

I was just doing some experiments of my own and found the results to be highly unpredictable. For example: near my home, at the mouth of the Chesapeake Bay (37°00.0' N, 076°00.0' W), the "watch error correction" of -00:45:32 worked great. However, near the Cape of Good Hope, South Africa (42°00.0' S, 018°00.0' E) the stars were not at all in the right positions, with or without the 45 min. correction. I'm using a highly accurate, free program called Stellarium to check VS' accuracy. I am very familiar with celestial navigation. (I know at least 4 sight reduction methods and have memorized the formulas from the Naut. Almanac. I also shoot and reduce actual sights and lunars on a regular basis with my own sextant here on the bay.)

This is all very disappointing because the whole reason I bought VS7 was to be able to practice sights when I don't have time to go out to the Bay. :( When I found out that this feature was/is broken, I felt like I totally wasted my money. (Although I do like VS7, I could've just stuck with ShipSim.)

P.S.
There is still no mention anywhere on the VS website that this feature does not work aside from the following which is buried in the "Sextant tutorial by Frank Sarfati":

Please note that in practice your “intercept” i.e. the difference between actual
elevation and calculated elevation, should be very small, in any event, less than 30
miles or 30 minutes of arc. You will notice that when doing sightings and lines of
position with data different than that used in this tutorial, you may find much larger
differences. The reason is that I’m not 100% sure of all the parameters of VS’ “celestial
mechanics” and there might be slight differences that I may have not taken into
account.


Seems like the least Ilan could do is let future prospective buyers know that if they're planning on buying the sim for the sextant feature not to bother.
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Re: Learning celestal navigation

Postby seanpatrick78 » Thu Jun 21, 2012 11:47 am

Bump.
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Re: Learning celestal navigation

Postby seanpatrick78 » Tue Feb 05, 2013 5:49 pm

This sextant is provided for the purpose of virtual celestial navigation, it was tested and found to have acceptable level of error like the one found in real observations.


This misleading statement still exists in the user's guide.
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Re: Learning celestal navigation

Postby Sailorjohn » Tue Feb 05, 2013 11:21 pm

You and many others don't seem to realize VS is DEAD. Gone. Finis. So complaining about needed updates isn't going to accomplish anything. VSF replaced it 4 years ago. I'd suggest you focus on asking Ilan to upgrade the celestial accuracy of VSF.
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Re: Learning celestal navigation

Postby seanpatrick78 » Sun Mar 17, 2013 11:59 am

It is not "gone". It's still offered as a product for purchase and it STILL has misleading (or at the very least, inaccurate) statements in the description.

Eg. the quote in my previous post:
...it was tested and found to have acceptable level of error like the one found in real observations.


...No, it doesn't.

Also, NB the bold text under the "Buy Now" button:

your opinion is important !


...is it?
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Re: Learning celestal navigation

Postby ron » Tue Mar 19, 2013 7:53 pm

Yeah, VS is not an accurate Sextant simulator.
Still I think there is value there if one realizes that with celestical navigation we are talking about different spheres of rotation....?
You can anchor your vessel (for simplicity) and (freeze time for simplicity) obtain a fix on the object, there are different spheres which your students will know about.
-Stellar
-Sun
-Moon
-Planets
Where on these four spheres date/time matters, for instance on the case of a Polaris fix in Stellar, and Sun and Moon for diameter, always.
VS doesn't cater for such.

What I'm saying is that with the VS limitations in mind, still there is a tremendous value add for any student when asked to explain why the VS fix is not an accurate one?
Is it time (stars)? Is it date for diameter (sun, moon)?

What VS does provide you is a sky with objects to use sextant on, of course it isn't real. But.... surely delivers a learning experience. Is up to you as a teacher, sometimes it is a better learning experience to find fault and be able to explain it, I would value those students high!
Shows they grasped the subject.

I have no comments on the commercial aspects of VS besides the above. (VS is not actually a sextant sim).
Cheers,

Ron
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Re: Learning celestal navigation

Postby ron » Tue Mar 19, 2013 8:12 pm

duplicate
Cheers,

Ron
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Re: Learning celestal navigation

Postby Calvin » Wed Apr 17, 2013 10:34 am

@Ron - Yes this is old, but I am wanting to follow the sextant tutorial. However, I am interested if it would be ok to use the VS sextant. Would you please comment on laukejas post? Thanks in advance.

laukejas wrote:While experimenting further, I noticed that sometimes, I cannot get a stars fix even with that 41:18 GMT adjustment you suggested.

Position:
39:42:52N
14:30:18E

Time: 02:27:25 (on sextant GMT, uncorrected)
Sighting Sirius. Elevation 27:29:06

Subtracting 41:18 from GMT (GMT becomes 1:46:07), I get my LOP off by 6.4nm
But if I subtract 40:18 (GMT becomes 1:47:07), LOP is off by 0.3nm, which is an almost perfect sight.

Any comment on that, Ron? Can you confirm my results in that scenario?
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Re: Learning celestal navigation

Postby ron » Wed Apr 17, 2013 4:55 pm

Hi, I would say that you discovered that the time off set (the VS time "error") possibly depends on lon/lat, so if you use a particular region all the time, use the off set you found? If I remember correctly (yes it is old), the scenery I used was Oslo Fjord by "the fat lady who sings", Charlotte.
But I'm pleased that the tutor has found a use, that particular feature (sextant use) in VS is an obscure and rarely used one, so thanks for taking it on.
Ron
Cheers,

Ron
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