  Alignment between real and virtual objects is a challenging task required for
the deployment of Mixed Reality (MR) into manufacturing, medical, and
construction applications. To face this challenge, a series of methods have
been proposed. While many approaches use dynamic augmentations such as
animations, arrows, or text to assist users, they require tracking the position
of real objects. In contrast, when tracking of the real objects is not
available or desired, alternative approaches use virtual replicas of real
objects to allow for interactive, perceptual virtual-to-real, and/or
real-to-virtual alignment. In these cases, the accuracy achieved strongly
depends on the quality of the perceptual information provided to the user. This
paper proposes a novel set of perceptual alignment concepts that go beyond the
use of traditional visualization of virtual replicas, introducing the concept
of COMPLEMENTARY TEXTURES to improve interactive alignment in MR applications.
To showcase the advantages of using COMPLEMENTARY TEXTURES, we describe three
different implementations that provide highly salient visual cues when
misalignment is observed; or present semantic augmentations that, when combined
with a real object, provide contextual information that can be used during the
alignment process. The authors aim to open new paths for the community to
explore rather than describing end-to-end solutions. The objective is to show
the multitude of opportunities such concepts could provide for further research
and development.
