Antonio A. F. Oliveira,  Luis Marcos Gonçalves. 

Consider the problem of morphing two simple differentiable closed curves composed of quadrics mantaining both topology and differentiability during the transformation. Here we indicate some partial results and some difficulties to get a morphing with those properties by using the fields of directions method.

http://sibgrapi.sid.inpe.br/rep-/dpi.inpe.br/banon/1999/03.15.17.18

Processando consulta.