MATLAB: Polar plot using polyfit

curve fittingimage analysisinterpolationMATLABplotsignal processing

I'm trying to fit the VALUES to make a polar plot but it seems I couldn't fit one value 1400e2 which the polyfit doesn't take it? what other function should I use to make the polar plot correct so that it contains the values exactly at that degree ?
VGV = [ 2000e2 1800e2 1600e2 1400e2 ]; % [0 45 90 135 ]  
angle  = (pi/180).* [ 0 45 90 135 ];
alpha  = (0:0.1:360);
alpha1 = (pi/180).*(0:0.1:360);
for k=1:1:length(alpha)
 
 p  = polyfit(angle,VGV,2);
 
 f = polyval(p,alpha1(1:1:901));
 f1 = fliplr(f(1:1:900));
 f2 = fliplr(f1);
 f3 = fliplr(f2);
 
 Vp = [ f f1 f2 f3];
 
end
figure;polar(alpha1(1:1:3601),Vp,'o')

Best Answer

It seems you want to fit a section between 0 and 135 degrees, then squish that to between 0 and 90, then replicate that around the circle for all 360 degrees. Seems kinds weird, but okay, whatever...
clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 22;
fprintf('Beginning to run %s.m ...\n', mfilename);
% Create training data.
VGV = [ 2000e2 1800e2 1600e2 1400e2 ]; % [0 45 90 135 ]
angleDegrees  = [ 0 45 90 135 ];
angleRadians  = (pi/180).* angleDegrees;
% Plot training data
polar(angleRadians, VGV, 'bo')
% Fit a quadratic
coefficients  = polyfit(angleRadians, VGV, 1)
% Create 90 more angles to fit between our training angles.
alpha = linspace(min(angleRadians), max(angleRadians), 90);
% Get a fit over 0-135 degrees only.
vFit = polyval(coefficients, alpha);
% Plot fitted data:
hold on;
% Make other quadrants
vFit360 = [vFit, fliplr(vFit), vFit, fliplr(vFit)];
t = linspace(0, 2*pi, length(vFit360));
polar(alpha, vFit, 'r-')
polar(t, vFit360, 'b-')
% figure
% plot(t, vFit360, 'b-');
% hold on;
% plot(alpha, vFit, 'r-', 'LineWidth', 2);
fprintf('Done running %s.m ...\n', mfilename);
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