*a*- Length of one elliptical axis
*b*- Length of shared elliptical axis
*c*- Length of another elliptical axis
- Orientation of model with respect to vertical
*t*- Thickness as a scale factor of the model

If *a*=*c* the model becomes an elliptical sampling region; if *a*=*b*=*c*the template models a circular sampling region.

By varying the parameters of the model, we can generate the desired blob
templates. The orientations of the normals at the boundary of the template
are also pre-computed by a template generation process. Note that the
orientation of the normals varies not only as a function of the angular
position on the sampling region but also as a function of the radius from the
center. The center of the model is a well defined point: it is the
intersection of the shared elliptical axis and the meeting point of the other
two axes (*a* and *c*).

The equations for an for an ellipse's boundary and its contour's normals are used to construct the templates [43]:

*a*- length of major axis (
*a*_{1}<*a*<*a*_{2}) *b*- length of minor axis (
*b*_{1}<*b*<*b*_{2}) - angle of ellipse minor axis with respect to vertical
*r*- radius
- angle between radius vector and boundary normal

Figure depicts a typical template consisting of a semi-circular annulus on top of a semi-elliptical annulus. The orientation values of the normals of the template are represented by intensity. Note the similarity of this template to the shape of a human head or face.