Biomedical Engineering Reference
In-Depth Information
The patches that get assigned to the same point on the sphere are aggregated
according to the shape categories of the surface components.
The concept of “shape spectrum” features is also included in the COSMOS
framework. This allows free-form object views to be grouped in terms of the
shape categories of the visible surfaces and their surface areas.
For the recognition purpose, COSMOS adapted a feature representation con-
sisting of the moments computed from the shape spectrum of an object view. This
eliminated unlikely object view matches from a model database of views. Once
a small subset of likely candidate views has been isolated from the database, a
detailed matching scheme that exploits the various components of the COSMOS
representation is performed to derive a matching score and to establish view
surface patch correspondence.
1.5.1.4
The “Spin Image” Surface Registration
Johnson and Hebert [30] presented an approach for recognition of complex
objects in cluttered 3D scenes. Their surface representation, the “spin” image,
comprises descriptive images associated with oriented points on the surface.
Using a single point basis, the positions of the other points on the surface are de-
scribed by two parameters. These parameters are accumulated for many points
on the surface and result in an image at each oriented point which is invariant
to rigid transformation.
Through correlation of images, point correspondences between a model and
scene data are established. Geometric consistency is used to group the corre-
spondences from which plausible rigid transformations that align the model
with the scene are calculated. The transformations are then refined and verified
using a modified ICP algorithm.
The spin image is generated by first considering an oriented point (a 3D point
with a normal direction) and defining its basis. The basis is defined using the
tangent plane perpendicular to the point direction and the point direction itself.
A spin-map is then defined using the point basis. In this spin map, any other
point on the surface is related to the oriented point by two parameters, one is
the perpendicular distance to the oriented point line direction and the other
is the signed perpendicular distance to the plane passing through the oriented
point and perpendicular to the point direction.
