由于矩阵的维数，MATLAB不会提取第一行和列

I am tracking an object that is thrown in the air, and this object governs a parabolic pattern. I'm tracking the object through a series of 30 images. I managed to exclude all the background and keep the object apparent, then used its centroid to get its coordinates and plot them. Now I'm supposed to predict where the object is going to fall, so I used polyfit & polyval. The problem is, I am tracking an object that is thrown in the a