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[Uzin]

Did anybody check DECLINE values  on stock maps ?

[Whiskey_Sierra_972]

I set decline in my mapmods as latitude....I must rework all settings in this way....but before I need more info about actual variation from latitude to declin value changes....

[greybeard]

Here follows a few examples:



it also shows actual variation from latitude to declin. Stock values have been picked from 4.13.

[Uzin]

I think Ardennes are more to south than Kurland, so why the noon sun is lower at Ardennes (both at summer ) ? It seems counter - intuitive, doesnt it ?
EDIT:
Excuse me, I was not right !

[Whiskey_Sierra_972]

Done a quick test on 2BTest map....

As a fictional map no data other than declin is taken in consideration....

My set on my map mods for all fictional test map are on stardard atmosfere:

[WORLDPOS]
CAMOUFLAGE = SUMMER
MONTH = 7
DECLIN = 45
PRESSURE = 760
TEMPERATURE = 15

Test plane: A5M...due open cockpit

Test place: the take off position of the strip with headling towards Nord that give a South headling for the plane at take off

Test with declin 45: Sun just above the windshield frame

Test with declin 5: Sun about at the zenith

Test with declin 90: Sun at the gunsight height

Test with Greybeard value (lat 45 and lon 45 on 15 july....about the middle of Caucasus)

90 - 66 = 24

Sun position: about 80° high....

I think that this should be the correct sun height....

In the next weeks I'll update all my mapmods worldpos and I'll release a data table for each declin value in the different months....please advise me if this data (for the 15 of each month) could be correct.

LATITUDE / SUN HEIGHT FEB / SUN HEIGHT MAY / SUN HEIGHT AUG / SUN HEIGHT NOV

[Whiskey_Sierra_972]

I think Ardennes are more to south than Kurland, so why the noon sun is lower at Ardennes (both at summer ) ? It seems counter - intuitive, doesnt it ?

Seem right because in my test a 90 of declin give a just above the horizont sun while the 0 of declin give me the sun height of about 90 degrees....so more less the declin more high the sun....

[greybeard]

Hi guys and thanks for the feedback!

As you already said, DECLIN, being the complementary angle of sun elevation, is inversely proportional to this latter. That's to say:

little DECLIN = higher sun (at noon)

I think proposed months are significant (an alternative could be the two couples of solstices and equinoxes), and day 15 is a wise choice. I must still understand, though, if and how DECLIN is recalculated from value set in the map; if yes, a correct setting would be just the right starting point for program spanning along campaign timeline.

[Whiskey_Sierra_972]

I have also thought about the solstices and equinoxes....but as those days are at the season change we haven't correct seasonal behaviour....this is why I use the middle month of the season....this give me the highest and lower daily mean in summer and winter while give small difference between spring and autumn....

[greybeard]

Right!

[Kopfdorfer]

Perhaps Map Declination ( and other map specification factors , for that matter ) should be accessible to mission and campaign designers within the FMB.
Just a thought.

Kopfdorfer

[greybeard]

I would just add a correction factor to take in account the "flat earth problem" mentioned at Reply #10.

I found it empirically, for the sole aerodrome of Libau (Kurland, where this problem is evident, cause the high latitude), but I believe it can be applied everywhere. Here, knowing actual sunrise time, I changed DECLIN on the map until I saw sun rising at actual time. Ratio between the two (calculated and watched) was 0.75, so this is the correction factor. I'm putting an example in Reply #6.

[WxTech]

My observations suggest DECLIN is actually latitude. When I keep a fixed latitude for a map and vary the month, the Sun track across the sky in the way expected of it.

Remember, the game is already applying the seasonal variation in solar elevation. Calculating the complement of the max Sun elevation is redundant, because you would have to do this ONLY if the game did not do this math already. Right now, calculating the complement angle is correct only for the spring and autumn equinoxes, when the sun is on the celestial equator. For other times well away from these two dates, you will introduce an error equal to the Sun's declination, up to 23.5 degrees at the solstices.

Declination is the astronomical term for celestial latitude in the equatorial coordinate system. So it makes a certain sense to take that meaning here, transposed to Earth's surface. But then, why not just adopt "LATITUDE"? Strange...

Anyway, I'm convinced that DECLIN is the latitude. Of course, the problem is that this applies over the whole map. A 600nm tall map would cover a latitude range of 10 degrees. Only a characteristic DECLIN value for about the middle would have to be chosen.