Real-time 3D visualization of space
https://celestiaproject.space/forum/
https://celestiaproject.space/forum/viewtopic.php?f=15&t=13784
PlutonianEmpire wrote:What are the all of the exact measurements used for Celestia?
Meaning, exactly how many kilometers is one AU, and exactly how many days is one year, and so forth?
I read the answer to those questions somewhere, but I forget where.
selden wrote:
Fridger,
When writing Lua orbital and rotation routines, one needs to use exactly the same values as Celestia is using. Too often, they are not the same as what one finds when searching with Google. The number of kilometers in an AU is one example.
"365.25," is that the exact number that celestia uses, or is it something slightly greater or slightly less? I've looked around, but couldn't find it.selden wrote:The number of days in a Terrestrial year is hardwired in the code in many places: 365.25
and that's just the first page of grep's output....$ grep 365.25 */*.cpp | more
celengine/astro.cpp: int64 d = (int64) floor((c - 122.1) / 365.25);
celengine/astro.cpp: int64 e = (int64) floor(365.25 * d);
celengine/astro.cpp: return (floor(365.25 * y) +
celengine/customorbit.cpp: return 365.25;
celengine/customorbit.cpp: m2 = jd19/365.2596407;
celengine/customorbit.cpp: double T = t / 365.25;
celengine/customorbit.cpp: double T = t / 365.25;
celengine/customorbit.cpp: double D = d / 365.25; // years
celengine/customorbit.cpp: t2 = t1 / 365.25;
celengine/customorbit.cpp: t3 = (t - 2433282.423) / 365.25 + 1950.0;
celengine/customorbit.cpp: t5 = t4 / 365.25;
celengine/customorbit.cpp: t8 = t6 / 365.25;
celengine/customorbit.cpp: t9 = (t - 2442000.5) / 365.25;
celengine/customorbit.cpp: double T = t / 365.25;
celengine/customorbit.cpp: double theta = degToRad(151.401 + 0.57806 * t
/ 365.25);
celengine/customorbit.cpp: return CreateJPLEphOrbit(JPLEph_Mercury, JPLEp
h_Sun, 0.2408 * 365.25, 6.0e7);
celengine/customorbit.cpp: return CreateJPLEphOrbit(JPLEph_Venus, JPLEp
h_Sun, 0.6152 * 365.25, 1.0e8);
I looked around in files in that link you gave me. I was using "year" and "days" as the search term.selden wrote:What do you mean by "looked around"?
In Celestia's source code or somewhere else?
it's in many of Celestia source files.and that's just the first page of grep's output....$ grep 365.25 */*.cpp | more
celengine/astro.cpp: int64 d = (int64) floor((c - 122.1) / 365.25);
celengine/astro.cpp: int64 e = (int64) floor(365.25 * d);
celengine/astro.cpp: return (floor(365.25 * y) +
celengine/customorbit.cpp: return 365.25;
celengine/customorbit.cpp: m2 = jd19/365.2596407;
celengine/customorbit.cpp: double T = t / 365.25;
celengine/customorbit.cpp: double T = t / 365.25;
celengine/customorbit.cpp: double D = d / 365.25; // years
celengine/customorbit.cpp: t2 = t1 / 365.25;
celengine/customorbit.cpp: t3 = (t - 2433282.423) / 365.25 + 1950.0;
celengine/customorbit.cpp: t5 = t4 / 365.25;
celengine/customorbit.cpp: t8 = t6 / 365.25;
celengine/customorbit.cpp: t9 = (t - 2442000.5) / 365.25;
celengine/customorbit.cpp: double T = t / 365.25;
celengine/customorbit.cpp: double theta = degToRad(151.401 + 0.57806 * t
/ 365.25);
celengine/customorbit.cpp: return CreateJPLEphOrbit(JPLEph_Mercury, JPLEp
h_Sun, 0.2408 * 365.25, 6.0e7);
celengine/customorbit.cpp: return CreateJPLEphOrbit(JPLEph_Venus, JPLEp
h_Sun, 0.6152 * 365.25, 1.0e8);
I worry that this literal value is hard-coded in so many places. Best practice would be to declare it once only (for example as days_in_year )and then use that variable/attribute in all these places.selden wrote:What do you mean by "looked around"?
In Celestia's source code or somewhere else?
it's in many of Celestia source files.
Chuft-Captain wrote:Best practice would be to declare it once only (for example as days_in_year )and then use that variable/attribute in all these places.