Get more exact x/y values from a curve fit

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Stefan Lang
Stefan Lang 2020-10-7
评论： Ameer Hamza 2020-10-7
I have some some point coordinates, that i get from annotation in an image. Let's say these are my x and y values.
x = (1:50);
y = x + randi(10,1,50) + sin(x);
Now i fit these
fitted = fit(x',y','smoothingspline');
To get the y values, i do
y_fit(:,1) = feval(fitted, x);
Plot returns a fitted curve with 50 points, but i need a much smoother curve fit. I need around 1000 x/y values from 10 annotated points.
plot(x,y)
hold on
plot(x,y_fit)
Now in my actual problems, i have e.g. 10 x values distributed over 1000 pixels. If i eval my fitted function, only get 10 y values back, but i need much more precise coordinates, to get a very smooth line through these 10 points, and not just connect 10 points in a linear manner. Goal is to annotate around 20 points in an 5000x2000 pixel image, fit a circle/polygon through these 20 points and use poly2mask() to get a logical array. But the circle should not just be a connection of the 20 points, but a much smoother curve.

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Ameer Hamza
Ameer Hamza 2020-10-7
编辑：Ameer Hamza 2020-10-7
What about fitting a low-order polynomial through your data-points
x = (1:50);
y = x + randi(10,1,50) + sin(x);
fitted = fit(x',y','poly4');
y_fit(:,1) = fitted(x); % this syntax is also valid
plot(x,y)
hold on
plot(x,y_fit)
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