z \rightarrow \frac{az + b}{\bar{b}z + \bar{a}}
If we identify \nabla_{-} with the interior of the shape, and \Gamma_{-} with the interior of the unit disk, then by the Riemannian mapping theorem there exists a map
\Phi_{-} : \nabla_{-} \rightarrow \Gamma_{-}
With the previous characteristics. Furthermore, if we identify \nabla_{+} with the exterior of the shape, and \Gamma_{+} with the exterior of the unit disk, the same conditions apply
\Phi_{+} : \nabla_{+} \rightarrow \Gamma_{+}
Now, we construct
\Psi = \Phi_{+} \circ \Phi_{-}
This provides a fingerprint of the shape unique up to a Moebius transformation.
In practice, we use the Swarz-Christoffel Matlab toolbox, having a complex variable with the given vertices coordinates in pol, we compute the map m by
pol=polygon(dots);
fc=diskmap(pol);
ex=extermap(pol);
iex=scmapinv(ex);
m=composite(fc,iex);
To extract the fingerprint, we need to evaluate the map in the z coordinate given the angle, so that z=exp(-i \theta), and the evaluation is m(z) for all \theta \in [0,2\pi). Now, the fingerprint is the angle of a given evaluation m(z), this is, \hat{\theta}=-\frac{log(m(z))}{i}. plotting (\theta,\hat{\theta}), we see the fingerprint.
Checkout the paper here.
Sir , I presently doing my phd in conformal mapping
ReplyDeletePlease help me to complete my degree
my mail id-vidyavijaya08@gmail.com
Hi there,
ReplyDeleteI am not an expert in conformal mappings. I used the previous conformal mapping to represent shapes of 2D objects so as to represent them and perform pattern recognition tasks.
I'm afraid I won't be able to help you.