interpolation matlab roipoly 2D

I have two matrices X and Y. They are the set of coordinates in my 2D xy plane. I want to interpolate between this points. What I really require is to calculate all the coordinates through which my interpolated curve will pass.

X=[1;4;4;2];
Y=[1,1,6,4];
X = [X(:);X(1)];
Y = [Y(:);X(1)];
If I do interpolation it should give me a quadrilateral figure. I want to get the coordinates through which my interpolated figure passes.

Till now I am using the roipoly function of MATLAB as follows.

I = imread('cameraman.tif');
Img=I;
I=double(I(:,:,1));
BW = roipoly(I,X,Y);
Now I can get the coordinates through which the figure passes.

Obviously some kind of interpolation is being done by roipoly. Is it different from normal cubic spline interpolation ? Will I get a better result if I use spline interpolation? How can I use it. It is imperative that I have to calculate the points through which the curve passes.

Answer 1

[praveen chandaliya]

roiploy function return type give coordinate [x, y, binaryImage, xi, yi] = roipoly(I);