MATLAB: How to get mask from boundary()

boundarybwboundariesmaskMATLAB

Hi,

I have points that represents curve levels. With thoses, I can find the boundary (k) matrix:

x = [1 2 3 4 3 2];

y = [4 5 5 4 3 3];

k = boundary(x,y);

I would like to make a mask from this boundary, but the function "boundary" does not provide the same output that "bwboundaries" does. Therefore, I cannot make a mask.

So, how can I make a mask with this data?

Best Answer

x = [1 2 3 4 3 2]';
y = [4 5 5 4 3 3]';
k = boundary(x,y);
plot(x,y,'.r')
hold on
patch(x(k),y(k),'k')

Related Solutions

MATLAB: How to create a mask array to specify a region which represents a cross sectional area (peculiar shape) and omit square regions from a meshgrid

L = 5*10 ;
B = 20 ;
nx = 100 ;
ny = 100 ;
x = linspace(0,L,nx) ;
y = linspace(0,B,ny) ;
[X,Y] = meshgrid(x,y) ;
%%Get 10X10 grids 
idx1 = (X>=10 & X<=20) & (Y>=10 & Y<=20) ;
idx2 = (X>=30 & X<=40) & (Y>=10 & Y<=20) ;
%%plot
plot(X,Y,'.r')
hold on
plot(X(idx1),Y(idx1),'Ob')
plot(X(idx2),Y(idx2),'Ob')

MATLAB: Problem using mesh. “Matrix is singular to working precision.”

Actually, the problem is that you do matrix operation but instead, you need to do elementwise operation, which means using ./ and .* instead of / and *. Try this:

[X,Y] = meshgrid([-3:0.01:3]); 
f1=@(X,Y) (3*X.^2.*Y + 10.*X.*Y.^2)./(exp(X.^2) + 3.*Y.^4) - (2.*X.*exp(X.^2).*(X.^3.*Y + 5.*X.^2*Y.^2))./(exp(X.^2) + 3*Y.^4).^2;
mesh(X,Y,f1(X,Y));

Best Answer

Related Solutions

MATLAB: How to create a mask array to specify a region which represents a cross sectional area (peculiar shape) and omit square regions from a meshgrid

MATLAB: Problem using mesh. “Matrix is singular to working precision.”

Related Question