RE: [Algorithms] Lightmap Terrain

[Pallister, K. <kim...@in...>]

Which could probably be hacked pretty well by calculating the directional
lighting/shadows, and the blurring the texture once or twice. Also, turning
up the ambient a little would help too.

Kim Pallister

We will find a way or we will make one.
                     - Hannibal


> -----Original Message-----
> From: Martin Fuller [mailto:mf...@ac...]
> Sent: Friday, August 25, 2000 3:18 AM
> To: 'gda...@li...'
> Subject: RE: [Algorithms] Lightmap Terrain
> 
> 
> The trouble with outdoor area's is the sky. If you have a 
> clear day you will
> get very hard edged shadows as the sun light comes down more or less
> parrallel. However if you have lots of cloud then the 
> sunlight that is not
> reflected back into space by the cloud layer tends to get 
> diffused alot on
> the ground. Thus there are no really hard shadows. 
> 
> Radiosity deals well with reflected light in shadowy areas it 
> does not deal
> very well with direct light. The best renders I have seen yet 
> in computer
> graphics are hybrid raytracing radiosity engines utilising 
> raytracing only
> for the specular light component and radiosity for the 
> diffuse. (I did see a
> paper on view depedant radiosity once but that thread of 
> though seems to
> have died)
> 
> A landscape is for all intensive purposes flat, the average 
> variation in
> altitude is pretty insignifcant compared to the size of the 
> planet. For most
> of the day except extremes of sunrise and sunset most things 
> will be in
> direct sunlight without shadow. Even during sunrise and 
> sunset because the
> world is nominally flat there is going to be very little 
> reflection where
> energy would bounce more than once of the world. The first 
> radiosity bounce
> is more likely than not to send energy straight back into 
> space or cloud. If
> you consider how much our atmosphere protects us from the 
> direct sun (in the
> first hit) any energy bounced back to the cloud layer and 
> then back to earth
> will have diminished to insignificant levels. Radiosity only 
> noticably works
> well in areas of shadow with flat surfaces. Texture (such as 
> grass) tends to
> scatter / average the light.
> 
> The trouble with the classic radiosity algorithm is that to 
> work it requires
> an enclosed environment from which energy cannot escape. 
> Trying to deal with
> this condition on a kind of universal scale provides all 
> sorts of headaches.
> A lamp in an entirely enclosed room with good flat surfaces 
> is much more
> trivial case. How Quake2 delt with energy loss from sky boxes 
> I don't know
> but I expect this was fudged and the sky box was allowed to 
> reflect energy.
> Certainly oudoor areas in Quake have always looked wrong 
> while the enclosed
> environments have been very convincing.
> 
> I would expect for outdoor situations raytracing to be the 
> most successful
> technique. For cloudy simply dropping the raycast and performing an
> averaging fudge (don't like that word but..) on the light 
> calculation to
> simulate radiosity bleed might be sufficient to give 
> convincing results. A
> full blown radiosity solution is likely to be expensive in terms to
> development time and processing and is IMO not going to give you good
> results.
> 
> Cheers,
> Martin
> 3D Programmer
> Shadowman2
> 
> 
> 
> -----Original Message-----
> From: Ivan-Assen Ivanov [mailto:as...@ha...]
> Sent: 25 August 2000 02:02
> To: gda...@li...
> Subject: Re: [Algorithms] Lightmap Terrain
> 
> 
> Neither embossing the heightmap nor dot-products work well. 
> The resulting lightmap doesn't give you any clue of where the depths
> and heights are (e.g. inverting the heightmap and moving the 
> sun at the
> opposite azimute produces the same image).
> I'm currently thinking about a simple raytrace, but I feel it will be
> effective
> only with low elevations of the sun over the horizon. We don't have
> any sharp features in the heightmap.
> 
> Has anybody tried "full" radiosity (whatever that means - 
> e.g. different
> reflectance/
> absorption for textures/ecosystems) on heightfields? Do you 
> think it would
> be worth the trouble?
> 
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