# can I equation of a curve from an image?

2 views (last 30 days)
Dekel Mashiach on 25 Apr 2022
Commented: Matt J on 25 Apr 2022
Is it possible to find the equation of a curve from an image?
I want to find the equation of the line in green:
Matt J on 25 Apr 2022
Note that even if your lines are parallel in the 3D world, they will geneally not be parallel in the 2D camera image, depending on the camera perspective. Likewise, the centerline in the 2D image will not correspond to the centerline in 3D.

Matt J on 25 Apr 2022
Edited: Matt J on 25 Apr 2022
This assumes your Image is already cast to type logical. The slope and intercept are for the center-line in matrix (row,column) coordinates.
reg=regionprops(Image,'PixelList');
x1=reg(1).PixelList(:,2);
y1=reg(1).PixelList(:,1);
x2=reg(2).PixelList(:,2);
y2=reg(2).PixelList(:,1);
A=[x1,x1.^0,0*x1;
x2,0*x2,x2.^0];
b=[y1;y2];
c=A\y;
slope=c(1);
intercept=mean(c(2:3));
Matt J on 25 Apr 2022
Edited: Matt J on 25 Apr 2022
I identify the lines by the camera and then create the green line in the middle of the lines. I want to find the green line equation. Here is the code for finding the green line:
If you already have the points on the green line, what prevents you from using fit(), lsqcurvefit(), or similar? Also, you have articulated that you want to model this as a polynomial, but of what order? Are you sure you don't need a piecewise polynomial? In any case, fit() offers all of these.