Hello, I have an image that does not contain linear segments (like that of buildings, roads, etc), and I want to create a superimposed 3D grid on top of it. Is there a way to find the vanishing points for a 2D perspective or is it not possible for this image? If you guys have a better way, please tell me.

 Ideally, I want the blue/green/purple balls (6 total) to be within a 3D grid.

I don't see any clever way to do it in Inkscape, other than to draw where you think it should be.

I'd try finding a way to export the model as a 3d file (stl, stp, obj, etc.), then put it in a 3d design program like cad to make the 3d grids. Then, export images that you can annotate.