Photogrammetry scaling to determine real world size in a .ply file

Hello everyone,

Is there a convenient way to retrofit a scale into a .ply file on Matlab using computer vision to recognize a shape? My issue is that I have an object which i have created a 3D model of, thinking that a scake would be applied to it since i had given the computer information on focal length and sesor width. It seems that no accurate scale was made though, so now i am hoping to have the computer recognize a certain shape on the object, and if i could tell it an exact dimension of that shape, the rest of the model could be scaled. I am using the computer vision toolbox.

Alternatively, i am thinking of starting over and applying a scale by placing something like a quarter into the model. Is this a reasonable way to go about scaling? How might i get MATLAB to recognize the quarter's size?

Again, my main issue is that i am having a difficult time working with my .ply file with computer vision. But alternatively, i may start over is working with .ply files in this manner is not practical