Inherently fail to the flat textureless surfaces or Occlusions and repetition or Non-Lambertian shading , specularities
즉 플랫하거나, 가려져 있거나 각도에 따라 보이는게 다르거나 광원이 번쩍이거나ㅎ
The similarity constraint is local so need to enforce global correspondence
constraints