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How do I calculate the position of the sun knowing
latitude / longitude and time?

I have a map, and i want locate the "sunshine" (dbprolight) into correct (really) place ( for correct shadows )

can someone write a sample code ?

The last time I did this, I just had it spin around the center of the game world at a really long range - then move it forward afterwards.

Maybe try converting the time to an angle, then position the sun with trig...

ang#=wrapvalue(timer()/10000.0)
sun_x#=sin(ang#)*100000.0
sun_y#=-50000.0+(cos(ang#)*100000.0)
sun_z#=0.0

Then position a sphere for example at sun_x#,sun_y#,sun_z# - and point it towards the centre of the game world (0,-50000,0 for example). It depends on how your positioning things, like usually it's a good idea to work out an estimate radius for your game world 'planet', so that the sun positioning can take that into account on the Y axis.

It's very basic and you probably have something more elaborate in mind, but it's ok for projects that don't need a lot of accuracy. It might be a good start that you can expand on.

Ok ...

But my map is in Really Word , Example :

Latit. =45.3872224
Langit.= 9.1222265

time (example) :16.15 Pm

were i put my sun ?

I see, really you need the MPL3D guy or something - people have done solar system models in DBPro, so someone will be able to provide decent help but you might have to wait a bit on them finding the thread.

Maybe you should ask these guys?
http://www.srrb.noaa.gov/highlights/sunrise/azel.html

...or this might help for a close approximation:
http://www.sunearthtools.com/dp/tools/pos_sun.php

...or you might be able to work it out from this spreadsheet:
http://www.docstoc.com/docs/17807456/Sun-Position-Calculator-Excel-Spreadsheet---Precision-Sundials-LLC-/

...isn't Google great!!

Tweaked my interest and I found best Google results by searching "sun position algorithm".

Possibly interesting one at:
http://stackoverflow.com/questions/257717/position-of-the-sun-given-time-of-day-and-lat-long

Mmmmmmm maths...

That looks relatively easy to translate...

can you translate this code ( from http://stackoverflow.com/questions/257717/position-of-the-sun-given-time-of-day-and-lat-long) ?


sunPosition <- function(year, month, day, hour=12, min=0, sec=0,
lat=46.5, long=6.5) {
twopi <- 2 * pi
deg2rad <- pi / 180

# Get day of the year, e.g. Feb 1 = 32, Mar 1 = 61 on leap years
month.days <- c(0,31,28,31,30,31,30,31,31,30,31,30)
day <- day + cumsum(month.days)[month]
leapdays <- year %% 4 == 0 & (year %% 400 == 0 | year %% 100 != 0) & day >= 60
day[leapdays] <- day[leapdays] + 1

# Get Julian date - 2400000
hour <- hour + min / 60 + sec / 3600 # hour plus fraction
delta <- year - 1949
leap <- trunc(delta / 4) # former leapyears
jd <- 32916.5 + delta * 365 + leap + day + hour / 24

# The input to the Atronomer's almanach is the difference between
# the Julian date and JD 2451545.0 (noon, 1 January 2000)
time <- jd - 51545.

# Ecliptic coordinates

# Mean longitude
mnlong <- 280.460 + .9856474 * time
mnlong <- mnlong %% 360
mnlong[mnlong < 0] <- mnlong[mnlong < 0] + 360

# Mean anomaly
mnanom <- 357.528 + .9856003 * time
mnanom <- mnanom %% 360
mnanom[mnanom < 0] <- mnanom[mnanom < 0] + 360
mnanom <- mnanom * deg2rad

# Ecliptic longitude and obliquity of ecliptic
eclong <- mnlong + 1.915 * sin(mnanom) + 0.020 * sin(2 * mnanom)
eclong <- eclong %% 360
eclong[eclong < 0] <- eclong[eclong < 0] + 360
oblqec <- 23.429 - 0.0000004 * time
eclong <- eclong * deg2rad
oblqec <- oblqec * deg2rad

# Celestial coordinates
# Right ascension and declination
num <- cos(oblqec) * sin(eclong)
den <- cos(eclong)
ra <- atan(num / den)
ra[den < 0] <- ra[den < 0] + pi
ra[den >= 0 & num < 0] <- ra[den >= 0 & num < 0] + twopi
dec <- asin(sin(oblqec) * sin(eclong))

# Local coordinates
# Greenwich mean sidereal time
gmst <- 6.697375 + .0657098242 * time + hour
gmst <- gmst %% 24
gmst[gmst < 0] <- gmst[gmst < 0] + 24.

# Local mean sidereal time
lmst <- gmst + long / 15.
lmst <- lmst %% 24.
lmst[lmst < 0] <- lmst[lmst < 0] + 24.
lmst <- lmst * 15. * deg2rad

# Hour angle
ha <- lmst - ra
ha[ha < -pi] <- ha[ha < -pi] + twopi
ha[ha > pi] <- ha[ha > pi] - twopi

# Latitude to radians
lat <- lat * deg2rad

# Azimuth and elevation
el <- asin(sin(dec) * sin(lat) + cos(dec) * cos(lat) * cos(ha))
az <- asin(-cos(dec) * sin(ha) / cos(el))
elc <- asin(sin(dec) / sin(lat))
az[el >= elc] <- pi - az[el >= elc]
az[el <= elc & ha > 0] <- az[el <= elc & ha > 0] + twopi

el <- el / deg2rad
az <- az / deg2rad
lat <- lat / deg2rad

return(list(elevation=el, azimuth=az))
}

Not tonight but I'll have a fumble with it tomorrow for you

...but I dare anyone to beat me to it!

This finds the Julian date and find which moon phases is at.

How do @HowDo!

By the way WTF is a Julian date?

Sounds like a date with a very dodgy character...

Google it.... It's simply how many days since Jan 1 for that year so that Jan 5th is Julian day 5.

Not quite, Wikipedia (!!) defines it as: "the interval of time in days and fractions of a day since January 1, 4713 BC Greenwich noon", which looks a similar concept to Unix timestamps, ie. A single number to represent time that is easy for computers to add/subtract.

Anyway, I looked some more and this site
http://www.stargazing.net/kepler/sun.html
has an example breakdown of the algorithm, with qbasic source. Easier to understand than that other example, written in `R` which looks to be a maths/science specific language.

Have fun, It was interesting reading about it all, and reinforced my belief that I suck at maths!