convert xy coordinates into binary matrix

I have XY coordinates of shape boundary. the points are double and I show an example on the figure. How can I represent these points in a binary matrix?

Thanks already

Answer 1

[Walter Roberson]

https://www.mathworks.com/help/images/ref/poly2mask.html

[AA]

I tried poly2mask but it does not show the point on the matrix.

[Walter Roberson]

poly2mask creates the binary matrix which is all you asked for in "How can I represent these points in a binary matrix?". If you want to display the binary matrix you can do so with

image(TheBinaryMatrix); colormap(gray(2))

or with

imshow(TheBinaryMatrix);

Or are you trying to create and display a binary matrix and also draw the original plot on top of it? Or is the problem that the displayed binary matrix is not blue line with a white background?

image(TheBinaryMatrix);
colormap([1 1 1; 0 0 1]);

[Daniel Devaprakash]

Hi Walter,

I have x (ranging from 3-4), y (0-1) coordinates of a contour (92 values); convert it into shape using alpha shape function, and then use the poly2mask function to obtain the binary image. The binary image matrix has 1 in only one element of the matrix and the rest are 0's.

For the binary image to represent the actual shape, I multiplied the co-ordinate values by 100, and then the binary image resembled the actual shape.

Code snippet:

          x = x.*100; y = y.*100;
          shape = alphaShape(x,y);
          shape.Alpha = 1;
          bw =poly2mask(shape.Points(:,1)',shape.Points(:,2)',256,256);
          imshow(bw); colormap([1 1 1; 0 0 1]);

Could you please let me know if this is the correct approach to solve this problem Thank you for your time and help.

Cheers,

Danny Devaprakash

[Walter Roberson]

You are retrieving the original points, not any information about the alpha shape implied by the points.

See https://www.mathworks.com/help/matlab/ref/alphashape.boundaryfacets.html or https://www.mathworks.com/help/matlab/ref/alphashape.inshape.html

[Daniel Devaprakash]

Hi Walter,

          Thank you for your help.

Cheers, Danny Devaprakash