Lpc2000

Somebody's doing fuel maps from the look of this, however fuel maps just 
aren't linear the way yours are. You may as well just set the start 
point and the end point thus:-
             0      3500
0         12      61
20       17      52
40       18      151
60       23      198
80       44      121
100     56       140

Then for example2300(rpm?) at 55kPa can easily be converted as follows:-

for 40kpa, 2300rpm point:

F1 = (151-18) * 2300/3500. Of course you would precalculate most of this 
so:-
F1 =  133/3500 * 2300. It makes sense to precalulate the increment /rpm, 
ie 133/3500
F1 =  0.038. In 0:16 (unsigned decimal format) this is equal to 0x09BA 
(2490)
F1 = 09BA * 2300 =  0x57.6318 (.038 * 2300 = 87.4)

Now repeast this for the second 60(kPa) row where rpm factor = 175/3500 
= 0.05 = 3277 or 0x0CCD
hence F2 =  0x0073.01CC (0.05 * 2300 = 115)

Now to interpolate the kpa part do (F2-F1)/(60-40)*(55-40)

Again you could speed this up by pre-storing the 60-40 or divide by 20 
as a binary decimal. Which happens to be 0.05 or 0x0CCD in 0:16 format so:-

F2 - F1 =  * 15 =  0x001B.9EB4 * 15 (this orders maintains lowest 
calculation error)  = 0x019E.4C8C

Now divide by 20 or multiply by 0x0.0CCD = 0x0014.B759DC1C => 20.716.

Finally add the 40kPa 2300 rpm value to this, keeping track of the DP = 
0x006C.1A71DC1C. returning to the land of 32 bits this is equivalent to 
108.103. Honestly a LOT simpler than it looks. With your tables having a 
hump you would only need to track the sign of results, which is possibly 
simpler than tracking signed arithmetic. Anyhow it comes down very simply:_

For each kPa point store the difference between 0RPM value and 3500RPM 
value divided by 3500 as a binary decimal.
This gives you 6 values in your scenario, call them K0 - K5, call the 
pressures at these values P'0 - P'5

read RPM (R), read kPa (P)(obviously if I have guessed wrongly 
substitute whatever the axes represent)
if P exactly matches one of the stored values Kn simply multiply RPM by 
Kn else
multply R * K(P'n<P) = Ix
multiply R * K(P'm>P) = Iy

next calculate  Ix + (Iy - Ix) * (P-P'n)/(P'm-P'n)

Might look a bit long winded, but by prestoring a lot of the calculable 
values you can run the calcualtions very fast.

Al




Rolf Bredemeier wrote:

> Hi,
>
> i'm searching for an example for 2d linear interpolation.
> The data is in an array unsigned char [10][400].
>
> Here is my "worksheet", may be, it help's to explain for i looking on:
> http://www.nur-solutions.de/tmp/2dinterpol.gif
>
> There is the way to solve  the prob. for x-value 55 and y-value 800 = 
> 59,35
>
> I need no floting point, unsigned char is only what i need.
>
> Best regards, Rolf
>
>
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