Surface based models are based on points in 3D space connected by lines which in turn form edges of polygons, the surfaces which distinguish these models. Many faces connected by their edges form an object. In the general case described here, it is not possible to make statements about the inside of the object. Objects are considered as hollow. We can render nice images from our models but we can not build these models based on an image.
Computer vision is still an unsolved problem.
The models do not have a meaning. In the worst case, a model is just a huge collection of voxels or polygons. This is because it is assumed that the final visualisation of the model will make its meaning clear to the sighted viewer. However, the meaning becoming clear is not always the case, and it is even less the case if a tactile version of this same model was presented to blind people. Many computer models today have at least a hierarchical structure and a label on each object.