Normals have been used in geometry acquisition and rendering for years.
However, modeling with normals is rather limited because of the lack of
formally defined operations. We present a variety of formal surface normal
operations built on two key ingredients. First, a separation of models in a
base surface and details, while the base surface is represented by positions
in a mesh, the details are only represented through normals in a parametric
space. Our operations can process the detail normals, while guaranteeing the
base surface remains unchanged. In this way, we do not require a
reconstruction step. Second, all our editing operations are performed in an
orthogonal projection. Besides being more intuitive for the user, normals in
an orthogonal mapping are in fact an RGBN image. This lets us define normal
operations including combination, sketching features, filtering, warping and
texture synthesis. We begin by defining operations contained in a single
chart, later we discuss global operations by using a partition of unity.

  Furthermore, we present an interactive system that implements these
operations using a texture atlas for storing geometric detail as normals.
This solution works with high resolution models and imposes no restrictions
on surface topology. In particular, our system uses point-based graphics to
build custom orthogonal charts. Next, it processes the normals and updates
the texture atlas. By using a temporary orthogonal editing chart, our system
presents the user with a transparent representation. It is not restricted to
processing in the original charts.