Re: [Jsbsim-devel] Multi-dimensional tables

[Bill G. <bi...@be...>]

Making up data in that case would only consist of repeating the first or
last value, since this method does not extrapolate. Specifying where the
smaller table (AOA 3 to 5 in this case) would probably be more painful and
less obvious for future support.

I created a fancy LFI routine in Ada a long time ago in a galaxy far, far
away, and one of the options that could be specified was if the values were
clamped at the first and last values, or if extrapolation could be used.
Most methods were used at times.

Bill




-----Original Message-----
From: Sean McLeod [mailto:se...@se...] 
Sent: Monday, June 10, 2013 8:50 AM
To: Development issues
Subject: Re: [Jsbsim-devel] Multi-dimensional tables

I think what Alan is asking/looking for is whether there is any sparse data
table support.

So for example if he has data for some coefficient that is dependent on 2
dimensions, say mach  number and AoA but for low mach numbers he has data
for a range of AoAs from say -5 to +20 but for higher mach numbers he only
has data for an AoA range from -3 to +5.

He doesn't want to be forced to make up data for the higher mach numbers for
AoA ranges from -5 to -3 and from +5 to +20 to match the AoA range of the
data he has for lower mach numbers.

Cheers

-----Original Message-----
From: Jon S. Berndt [mailto:jon...@co...]
Sent: Monday, June 10, 2013 2:27 PM
To: 'Development issues'
Subject: Re: [Jsbsim-devel] Multi-dimensional tables

> Is this conditional able to cope with the incidence range of 
> coefficients decreasing with Mach No?
> 
> By this I mean that, for most aircraft,  at low speed the incidence 
> range is quite high, but at high speed the incidence range is much 
> lower. It seems silly to populate tables with data that is difficult 
> to estimate and will never be used.
> 
> Alan

I'm not sure I understand your question. Any tables defined are standard
JSBSim tables with data suitable for your aircraft. I'm guessing that most
people will not use the capability described in the original post, but for
very large databases derived from extensive wind tunnel testing and/or CFD,
the capability to model aero data higher than 3 dimensions may be needed.
The mechanism for doing that was presented. It is up to the modeler to
decide if that is needed or appropriate. In my case, with a very detailed
aero database that is nearly a quarter million lines long, it is.

Jon



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