Date, Time, Place and twilights in X-Plane, but not only....

[jcomm 5,928]

I'm that picky simmer who keeps asking for features probably most simmers would really not bother at all looking for...

 

One of these features is the proper rendering of daylight, something that unfortunately few flight simulators do.

 

Given a date, a time ( Zulu or Local ), and placing your aircraft / viewpoint at a given place on Earth you should be able to have the Sun, and preferably the Moon ephemeris correctly implemented, and a good rendering of twilight periods ( civil dawn and civil dusk, at least ), and the correct daylight according to that date-time/place.

 

Only 3 flight simulators do it properly at present ( maybe 4, counting AEFS2, but I do not have sufficient data about that one... ). X-Plane fails miserably during dawn or dusk periods, depending on epoch of the year and latitude of the place. It can sometimes be more than 1 hr away from reality in terms of Sunset / Sunrise times, and the Moon - simply forget about that one...

 

But even Aerowinx PSX doesn't do a good job, particularly on dusk twilight, becoming pitch dark in most situations when in real life there is already / still plenty of twilight...

 

FSX / P3D, ELITE and - believe it ot not... - IL-2 Battle of Stalingrad do it almost perfectly, with IL2 being restricted to just a small area of the Planet though. ELITE is even more realistic than FSX / P3D, and all of the three properly represent the Sun and Moon ephemeris!

 

Flight Gear was supposed to do a good job too, but it doesn't, at least in the latest nightly release, where it looks almost like X-plane in being away from reality in terms of dusk twilights...

 

I would really like to see these items addressed by LR for their upcoming XP11.

[Murmur 3,941]

FSX / P3D, ELITE and - believe it ot not... - IL-2 Battle of Stalingrad do it almost perfectly, with IL2 being restricted to just a small area of the Planet though. ELITE is even more realistic than FSX / P3D, and all of the three properly represent the Sun and Moon ephemeris!

 

Flight Gear was supposed to do a good job too, but it doesn't, at least in the latest nightly release, where it looks almost like X-plane in being away from reality in terms of dusk twilights...

 

As I said, FlightGear does a decent job as well, you just have to disable Atmospheric Light Scattering.

 

Here it is civil twilight (sunset and then civil dusk):

 

 

 

In term of ambient lighting, quite close to the corresponding screenshots of Elite you posted in the Aerofly thread (maybe a bit darker, but FlightGear tend to be a bit too dark even during daylight, so increasing the general bightness should improve things all around).

 

If using Atmospheric Light Scattering, things can be improved a bit by using filters (in the Atmospheric Light Scattering menu) and increasing brightness. Still a bit too dark though, disabling atmospheric scattering remains the best thing to do.

 

Default brightness:

 

 

Max bightness:

 

 

As a side note, why always use desparaging remarks ("fails miserably", etc.) for all of the other simulators that aren't your transitory choice of the moment?  :smile: Seems like a constant need to reinforce the auto-belief that the temporary chosen one is the only worth. I think every flight simulator has its nice features, strong points, and flaws, but they all do a nice job after all.

[jcomm 5,928]

Heheh, a agree regarding the emphatic "miserably"... :-)

 

But there are actually three sims doing the right calculations in this case - ELITE, FSX/P3D and IL2 BoS...

 

Well, regarding your pictures, it depends on the place and time... You have to get a sunrise / sunset table, or simply the site I linked above, and check if twilight is correctly displayed depending on time. That's where the problem lays, not on the graphic effects themselves which look plausible in FG.

 

And, at what place did you run those tests Murmur ? At that place and at this time of the year, is it really of 2hrs the difference between LT and UTC ?

 

I've been running a few more tests and what happens is that apparently FG has problems with UTC calculations and relating UTC with Local Time.

 

Even when I use something like:

 

--start-date-gmt=2016:09:06:02:51:00

 

​​or

 

--time-match-real

 

to start FG, in this case in such a way that it starts at 02:51:00 UTC on September 6, 2016, in FG it reports being 01:51 UTC. If we then advance manually the time to 02:51, and do the same for the Sunset, it more or less agrees with Sunrise / Sunset times.

 

At most places the reported difference between LT and UTC is incorrect though, and that is the main reason for the wrong display of twilight periods.

 

I have also been experimenting with and without "Atmospheric Light Scattering".

[Murmur 3,941]

Well, regarding your pictures, it depends on the place and time... You have to get a sunrise / sunset table, or simply the site I linked above, and check if twilight is correctly displayed depending on time. That's where the problem lays, not on the graphic effects themselves which look plausible in FG.

 

And, at what place did you run those tests Murmur ? At that place and at this time of the year, is it really of 2hrs the difference between LT and UTC ?

 

I've been running a few more tests and what happens is that apparently FG has problems with UTC calculations and relating UTC with Local Time.

 

The pictures have been taken at LIRP in Italy, and yes I used a website for the calculation of sun position and the ephemeris of FlightGear perfectly agrees, so what you see in the pictures is the actual civil twilight (sun elevation between -0.833 degrees and -6 degrees). The difference between Local Time and UTC is also correct (with Daylight Saving Time, it's UTC+2 hours in Italy).

 

I don't know if there are discrepancies between LT and UTC in other places in FlightGear, but I don't see that as particulary important, since what really counts is UTC and the ephemeris in FlightGear is of course spot on when evaluated using UTC.

[jcomm 5,928]

Not at all places Murmur, as you can easily check, for instance at ENBO, using UTC only...

[Murmur 3,941]

Not at all places Murmur, as you can easily check, for instance at ENBO, using UTC only...

 

And here it is, ENBO, civil dusk at 5:11 Local Time (3:11 UTC) today 11 September.

UTC/LT difference is also correct, according to the sun position website you linked in the other post:

 

[jcomm 5,928]

Hmmm, I just checked here and for Civil Twilight - 5:11 until 6:07 LT, it corresponds in FG to 0:11 until 1:07. My FG is giving 3 hours difference between UTC and LT for ENBO...

 

But I was just about to post that if I completely forget about CEST and LT, and use only UTC as a reference it works acceptably.

 

Bellow what I get in my FG, for same situation / date. And in fact Atmospheric Light Scattering is worse...

 

[DocBird 79]

Sorry, but I couldn't care less...

 

I hope that LM does not invest one minute of development time in this "issue". They have certainly enough other topics to deal with.

[Janov 2,383]

Sorry, but I couldn't care less...

 

I hope that LM does not invest one minute of development time in this "issue". They have certainly enough other topics to deal with

 

I fully agree with DocBird. I suggest to UNINSTALL X-Plane until this is fixed. :wink:

[Murmur 3,941]

Sorry, but I couldn't care less...

 

I hope that LM does not invest one minute of development time in this "issue". They have certainly enough other topics to deal with.

 

LM? Maybe you mean Laminar Research?

 

In any case, to each his own, as they say. You may dismissively use quotation marks for this "issue", but for some people, having the environment pitch black in the sim when there should actually be plenty of light, may be annoying.

 

Moreover, it can also be of interest if one is simulating VFR flights in the vicinity of civil twilight, so it's far from being just a cosmetic issue.

 

And yes, I hope LR invests all the time needed to correct this issue (since FSX/P3D/FlightGear/etc. have always had it a lot more accurate).

 

Moreover the time needed to correct the issue is probably trivial, and I speak by experience because I modified myself the relevant shaders to improve the lighting at twilight, but the one thing that cannot be modified is the actual sun position that is off by 2 or 3 degrees, and is hard coded inside X-Plane.

[Jimmy RFR 406]

Each to their own. While I would consider this to be of a lower priority than say, seasons, I'd like to see it improved as well. I love taking early dawn or dusk flights, and the time required to fly in such is often wildly off, at least where I live.

 

And... if there were proper seasons in the sim, giving me a reason to fly at different times of the year, it would be of even more importance.