# Projecting a dataset on an ellipse

9 visualizaciones (últimos 30 días)
Salad Box el 8 de Dic. de 2022
Comentada: Matt J el 16 de Dic. de 2022
Hi,
I fit an ellipse (in green) to my dataset (white dots).
I'd like to project each data point on the ellipse (or shifting each data point onto the ellipse using the shortest distance). Those projections on the ellipse will form a new set of data. How can I achieve this?
##### 2 comentariosMostrar NingunoOcultar Ninguno
Jonas el 8 de Dic. de 2022
if you have the ellipse and your x and y corrdinates, use the interp2() function with the 'nearest' interpolation method
Salad Box el 12 de Dic. de 2022
Thank you. I will give it a try.

Iniciar sesión para comentar.

### Respuestas (1)

Matt J el 12 de Dic. de 2022
function Xp=ellipseprj(Q,xc,X0)
%Projects given 2D points onto 2D ellipse
%
% Xp=ellipseprj(Q,xc,X0)
%
%IN:
%
% Q,xc: Ellipse equation matrices. Q is 2x2 and xc is 2x1 such that
% ellipse equation is (y-xc).'*Q*(y-xc)=1
% X0: 2xN matrix of points to be projected
%
%OUT:
%
% Xp: 2xN matrix of projected points
N=size(X0,2);
xc=xc(:);
[Rt,D]=eig(Q);
Rt=real(Rt); D=real(D);
iD=diag(1./diag(D));
iDsqrt=sqrt(iD);
b=-iDsqrt*Rt.'*bsxfun(@minus,xc,X0);
Yp=nan(size(X0));
for i=1:N
Yp(:,i)=trustregprob(iD,b(:,i),1);
end
Xp=bsxfun(@plus, Rt*iDsqrt*Yp,xc);
##### 2 comentariosMostrar NingunoOcultar Ninguno
Salad Box el 16 de Dic. de 2022
% Q,xc: Ellipse equation matrices. Q is 2x2 and xc is 2x1 such that
% ellipse equation is (y-xc).'*Q*(y-xc)=1
I still don't fully understand what Q and xc is.
What do you mean by ellipse equation (y-xc).'*Q*(y-xc)=1?
Matt J el 16 de Dic. de 2022
Every ellipse obeys an equation of that form. I've given an example over in your duplicate post,

Iniciar sesión para comentar.

### Categorías

Más información sobre Least Squares en Help Center y File Exchange.

### Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by