Re: [Jsbsim-devel] Multi-dimensional tables

[Dennis J. L. <js...@li...>]

So, Jon, (without looking at the code) will this work for Alan?

<function name="bigWhatever1">
  <interpolate1d>
    <p> velocities/mach </p>
    <v> 0.1 </v>  <interpolate1d>
                  <p> ???/alpha </p>
                  <v> -10.0 </v>  <v> ?? </v>
                  <v>   0.0 </v>  <v> ?? </v>
                  <v>  30.0 </v>  <v> ?? </v>
                 </interpolate1d>
    <v> 0.9 </v> <interpolate1d>
                  <p> ???/alpha </p>
                  <v> -2.0 </v>  <v> ?? </v>
                  <v>  0.0 </v>  <v> ?? </v>
                  <v>  5.0 </v>  <v> ?? </v>
                </interpolate1d>
    <v> 2.0 </v> <interpolate1d>
                  <p> ???/alpha </p>
                  <v> -1.0 </v>  <v> ?? </v>
                  <v>  0.0 </v>  <v> ?? </v>
                  <v>  1.0 </v>  <v> ?? </v>
                </interpolate1d>
  </interpolate1d>
</function>

I'm guessing yes, by the way that you describe the tables since the
dependent value can be a table/function, etc.  So each dimension needs
to be calculated separately at two different breakpoints and then
interpolated.  (The traditional, orthogonal, multi-dimensional matrix
approach has only a single set of breakpoints in each dimension then
uses integer indices to get into the table, therefore, it has to be
"full".)   If it is just linear in each dimension, it should work, right?

Dennis

On 2013-06-10 10:23 AM, Alan Teeder wrote:
> 
> Yes Sean got the words that I meant. ;-) Thanks.
> 
> What I am looking for is a way to break up the coefficient tables into 
> sections that are split into the high alpha ranges that are applicable at 
> low speeds, and low alpha ranges which are achievable at high speeds.
> 
> My WIP stalls at 30 degrees incidence on the approach, but would probably 
> break the airframe at 5 degrees when supersonic.
> 
> At the moment each coefficient has a table covering the whole incidence 
> range for each Mach number, so in this case the tables cover the range -10 
> to 40 degrees incidence and Mach numbers 0-2. .
> 
> My solution at the moment is to extrapolate the data to make up numbers to 
> fill in the grid at the high speed end, but these numbers are really just 
> meaningless rubbish and are only there to complete a sparse matrix.
> 
> -----Original Message----- 
> From: Jon S. Berndt
> Sent: Monday, June 10, 2013 3:01 PM
> To: 'Development issues'
> Subject: Re: [Jsbsim-devel] Multi-dimensional tables
> 
> Ah, yes - thanks for that. That explains it. JSBSim table lookups only do
> gridded tables - not ungridded/sparse. There are a number of methods one
> could take to fill in the blanks and IMHO it's better to do that offline.
> It's sort of an art, in my experience.
> 
> Jon
> 
>> -----Original Message-----
>> From: Sean McLeod [mailto:se...@se...]
>> Sent: Monday, June 10, 2013 6:50 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