--- Christian Mayer <[EMAIL PROTECTED]> wrote: > David Megginson wrote: > > > > Christian Mayer writes: > > > > > As I wrote before, there's a function in the > WeatherCM code that > > > calculates the air pressure based on the air > pressure at a given > > > altitude and at a given teperature profile. It > is based on the well > > > known (but incorrect) baryometric (SP?) formula > but doesn't suffer from > > > its limitations. When you feed it, the standard > conditions it will > > > return the standard atmosphere. > > > > > > When you adopt that code, you'll automagicly > get the correct results. > > > > Does the code handle only pressure? > > The code does only calculate air pressure. > > > There are a few fairly good > > atmosphere models I can adapt (including the one > in JSBSim); > > The code does comply with the international > atmosphere models (IIRC > JSBsim uses exactly the same data I used to verify > the calculations) > > > I just > > stuck with the tables for now because they keep > the code fast and > > simple. > > Tables are faster and simpler. But they aren't > really flexible. > When you are concerned about performance: How many > pressure calculations > do we need? Not more than a few per frame. And as > the pressure changes > are very small during a frame we can even cache the > result. And > alltogether the number of calculations that are done > is very small. > Probably the space overhead a table generates would > be worse (cf. > discusion about inlining code) > > > I want to be able to extrapolate both ways -- if > the user > > supplies a temperature or pressure at altitude, I > want to be able to > > extrapolate the temperature or pressure at sea > level, and vice-versa. > > So the code is better suited for you than the > tables. > > You give the code a temperature profile (which is > basicly the table > approach) and a pressure value at a give altitude > (doesn't need to be > sea level). Then you get valid numbers for any > altitude that you want. > > CU, > Christian > > PS: As the air pressure curve is similar to the > e-function (e^altitude) > it's nowhere linear and thus badly approximated by a > table...
Depends on how many points are in the table. > > > -- > The idea is to die young as late as possible. > -- Ashley Montague > > _______________________________________________ > Flightgear-devel mailing list > [EMAIL PROTECTED] > http://mail.flightgear.org/mailman/listinfo/flightgear-devel > > __________________________________________________ Do You Yahoo!? Yahoo! - Official partner of 2002 FIFA World Cup http://fifaworldcup.yahoo.com _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
