> But this is definitely some food for the brain. > Here is what they write: > > So, how do we render these clouds in x-plane 10? >> >> the answer is levels of detail, which is a display of resolutions of >> buckets. (...) >> AGAIN! >> NO MATTER HOW BIG THE SKY, EACH LEVEL OF DETAIL ONLY COSTS US 1,000 >> PUFFS!
Cutting through all the excitement of the blog writer - we've been discussing this previously, and (at last I) disregarded it for the following reasons: 1) Using many small 'puffs' (or 'sprites' in Stuart's terminology, or 'cloudlets' in mine) are a nice way to render diffuse shapeless clouds, but to arrange them in such a way that you get the correct shape of a well-defined Cumulus cloud is near impossible (which is way we use not so many larger full-cloud image textures). 2) Setting up 'puffs' of different size dependent on distance in a static setup is all nice and crispy, but unfortunately the darn airplanes *move*, so you need some algorithm which replaces a collection of small puffs by a single large puff - and this transition shouldn't actually be visible. If you code it for just a few configurations, it can be done, but then your clouds lack variety. 3) The problem that follows from the above two is that you must make a transition from a Cu cloud composed of 100 small puffs to one which is a single large puff, but the cloud shouldn't change visibly while you do so - which is tricky because Cu clouds have a lot of structure. 4) The problem is worsened by the fact that Cu clouds are not exactly self-similar across too large distance scales - a single puff which works well to represent a cloud from the distance isn't represented well by 10 smaller versions of the same puff - the shape gets wrong. Instead, you'd need a mixture of different smaller puff types dependent on where in the cloud you are. 5) Talking about km-sized puffs at distance is all nice, but the cloud layer may just be 100 m thick, so you can't represent it by 1000 m scale puffs without making it thicker than it really is. Again, with shapeless clouds you can use z-rescaling to deal with the problem, but with structured clouds, that shows up in a very pronounced way. My guess is that X-plane with this approach invites trouble with representing cloud structures, but fares better with very featureless clouds. Also, shape variation of clouds might be an issue, dependent on how this is coded in detail. It's not a bad idea, but the devil is in the detail, and a dynamical way of doing a reduction of complexity at distance (= the imposters) seems a better way to me. Anyway, it's hardly like this writer invented the wheel... Cheers, * Thorsten ------------------------------------------------------------------------------ Cloud Services Checklist: Pricing and Packaging Optimization This white paper is intended to serve as a reference, checklist and point of discussion for anyone considering optimizing the pricing and packaging model of a cloud services business. Read Now! http://www.accelacomm.com/jaw/sfnl/114/51491232/ _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
