Irrlicht for 3D planetarium

Petro · Post by **Petro** » Sun Nov 19, 2006 4:24 pm

Do you think it would be a good idea to use Irrlicht as a graphical engine for 3D planetarium. I am concerned about several things.

1. Scale & Precision. Would the engine suit for modelling small objects (1 - 10 arb. units) wide distance apart (40-50 thousand of same units)

2. Shadow casting. I am also planning to model some eclipses. Would the volume shadow casting allow me to do that with high accuracy taking into account the size of the objects and very large distance between them.
Thanks.

omar shaaban · Post by **omar shaaban** » Sun Nov 19, 2006 4:30 pm

aaa yes it can

bitplane · Post by **bitplane** » Sun Nov 19, 2006 5:05 pm

no it cant. pluto is over 3500 million miles away from the sun, so if you want accuracy to 100th of a mile you're going to need at least 40 bits of precision, f32's only have 24.
f64s will have enough accuracy, but even if irrlicht could use these for coordinates (it can't) you wouldn't be able to draw them without flickering because from a distance your depth buffer resolution would be wider than the distance from the earth to the moon.
you're going to need your own coordinate system, then convert irrlicht's coordinates for drawing, drawing things which are outside the camera's view from back to front without z-buffer like a skybox... and shadows are gonna be hard

sio2 · Post by **sio2** » Sun Nov 19, 2006 6:53 pm

bitplane wrote:no it cant. pluto is over 3500 million miles away from the sun,...

The irony is the book that bitplane (Holly) is reading.

bitplane · Post by **bitplane** » Sun Nov 19, 2006 8:04 pm

The Junior Colour Encyclopedia of Space has never failed me yet

rogerborg · Post by **rogerborg** » Sun Nov 19, 2006 10:06 pm

The nearest actual planet to your actual sun is... Mercury.

No, Venus. No, Mercury again. Venus. Mercury. Earth. Mercury.

Damn 32 bit floats.

luckymutt · Post by **luckymutt** » Mon Nov 20, 2006 3:25 am

sio2 wrote:
bitplane wrote:no it cant. pluto is over 3500 million miles away from the sun,...
The irony is the book that bitplane (Holly) is reading.

Nah, that's not irony.
Besides, screw pluto. Dirty wad of ice masquerading as a planet...'bout time we gave it the boot.

More on topic, surely there would be a way to fake the distances. For example, scale the distance down equally proportionate to scaling down its size or some such, and adjusting the rotation to match.
Of course, you would then have to do the same for some of the other planets with a different scaling factor according to their distance out.

Maybe?

jam · Post by **jam** » Mon Nov 20, 2006 6:23 am

Use a logarithmic scale for distances.

luckymutt · Post by **luckymutt** » Mon Nov 20, 2006 11:11 am

HA!!
"Logrithmic" !!!
That was the word I was looking for.

hybrid · Post by **hybrid** » Mon Nov 20, 2006 12:45 pm

Now that Pluto is no planet anymore you can simply skip it unless you'll also do a Sub-Planet-arium

FistBall · Post by **FistBall** » Mon Nov 20, 2006 11:57 pm

have you seen Stellarium? quite nice, and it's cross-platform
http://www.stellarium.org/