Calculate altitude meters from pressure pascals (Pa->m)

alt_calc.m

%fast altitude calculation based on:
%https://en.wikipedia.org/wiki/Pressure_altitude
%(1-(millibars/1013.25)^(0.190284))*145366.45 = feet

%Bounds setup:
paMin = 69683;
paMax = 106597;
stepCount = 500; %number of values to plot

%setup pa vector
interval = round((paMax - paMin) / stepCount);
pa = paMin:interval:paMax; %pressures in pa
pa = [pa 106597];

%calculate result using the wiki equation:
fullResult = getAltFromPa(pa);
%csvwrite('rangeResult.txt', fullResult); %(opt) write results to file

%Get results for specific values. Right now I just use this as bounds...
specificValues = [69682 106597]
specificResult = getAltFromPa(specificValues)

%plot
figure('name', "Pressure to altitude")
clf
plot(pa, fullResult)
hold on

%(opt)load the lookup table from turbotrig and use it to calculate alt
%values corresponding to the pressure values in pa
%alt_lookup_table = csvread('currentValues.csv'); %read in the csv of currently used values for fast_alt
%currentlyUsed = calcLikeFastAltFunc(pa, alt_lookup_table);
%plot(pa, currentlyUsed, 'r')
%plot(specificValues, specificResult, 'r*');

xlabel('Pressure (Pa)')
ylabel('Altitude (m)')
hold off

function altMeters = getAltFromPa(paVec)
    mbars = paVec .* .01; %convert to millibars
    altFeet = (1-(mbars./1013.25).^(0.190284)).*145366.45;
    altMeters = altFeet .* 0.3048;
end

function currentVec = calcLikeFastAltFunc(paVec, alt_lookup_table)
    %this implementation is not ideal... just a quick copy pasta from
    %turbotrig
    paMin = 69683;
    paMax = 106597;
    t = length(paVec).*(paVec-paMin)./(paMax - paMin);
    index = round(t) + 1;
    dp = t - index;

    currentVec = [];
    for i=1:length(index)
        if index(i) < (500)
          toAdd = alt_lookup_table(index(i))/10 + dp(i)*(alt_lookup_table(index(i) + 1) - alt_lookup_table(index(i)))/10;
        else
          toAdd = alt_lookup_table(i)/10.0 + dp(i) * (alt_lookup_table(i) - alt_lookup_table(i - 1))/10.0;
        end
        currentVec = [currentVec toAdd];
    end
    
end