MATLAB: I want to generate a square or rectangular array. and that array should contain desired numbers in a circle or elliptical contourwith some radius and all other numbers should be zero. Can anyone help me in this

arraycontourlogical operatorsMATLAB

I have an array of values, which is either square or circular in nature, which is as a function of x and y coordinates. I want to create a circular contour that contains a desired/input values, The contour should be like circule or elliptical, in that contour the desired values should be present. In all other places the number should be zero.

Best Answer

r = 1. ;
th = linspace(0,2*pi,500)' ;
x = r*cos(th) ; y = r*sin(th) ;
m = 500 ;n = 500; 
xi = linspace(min(x),max(x),m) ;
yi = linspace(min(y),max(y),n) ;
[X,Y] = meshgrid(xi,yi) ;
idx = knnsearch([X(:),Y(:)],[x, y]) ;
Z = zeros(size(X)) ;
Z(idx) = 1 ;
pcolor(Z)
shading interp

Related Solutions

MATLAB: Matlab code for generating some shapes using signed distance

I had to read a bit about "signed distance fields" and came across this blogpost

https://blogs.mathworks.com/graphics/2016/03/07/signed-distance-fields/

Have your read it? Should not be too hard to implement for your shapes.

I would attempt the following more 'general' algorithm.

describe the shape with a set of x-y-coordinates
create a mesh
find the closest distance to each point in the mesh to the set of x-y-coordinates

If I understand correctly, that is what the "signed distance field" describe, i.e. the closest distance to a shape from any point in the domain.

This is the code for a single horizontal line from [0,0.5] to [1,0.5].

% The "shape"
x=0:0.01:1;
y=ones(size(x)).*.5;
% The "domain"
[X,Y] = meshgrid(0:0.01:1,0:0.01:1);
% Closest point between domain and shape
[X,Y] = meshgrid(0:0.01:1,0:0.01:1);
[id,Z] = dsearchn([x',y'],[X(:),Y(:)]);
scatter3(X(:),Y(:),Z,[],Z)

The only thing you have to change is the sign of those points that are inside of the "shape". This is however fairly simple, using the inpolygon function. Let's try one for the sinusoidal shape:

% Build polygons
x=0:0.01:1;
Y{1} = 0.2.*sin(x/0.05)+0.3
Y{2} = 0.2.*sin(x/0.05)+0.7
py = [Y{1},fliplr(Y{2})] 
px = [x,fliplr(x)];
% Define domain
[X,Y] = meshgrid(0:0.01:1,0:0.01:1);
% Calculate distance
[~,Z] = dsearchn([px',py'],[X(:),Y(:)]);
[in]=inpolygon(X(:),Y(:),px,py)
Z(in) = -Z(in)
Z = -Z;
% Plot
surf(X,Y,reshape(Z,size(X)),'edgecolor','none');hold on
p = polyshape(px,py)
plot(p)
axis([0 1 0 1])

There seems to be some edge-effect, in particular to the left. Other than that, it looks quite OK.

MATLAB: 2D density plot with colorbar

N = 100 ; 
x = linspace(0,2*pi,N)' ; 
y = sin(x) ; 
xi = linspace(min(x),max(x),N) ; 
yi = linspace(min(y)-1,max(y)+1,N) ; 
[X,Y] = meshgrid(xi,yi) ; 
Z = zeros(size(X)) ; 
idx = knnsearch([X(:) Y(:)],[x y]) ; 
Z(idx) = 1 ; 
Z(idx+1) = 1 ; 
Z(idx-1) = 1 ; 
pcolor(X,Y,Z)
shading interp
colorbar
colormap(jet)

Best Answer

Related Solutions

MATLAB: Matlab code for generating some shapes using signed distance

MATLAB: 2D density plot with colorbar

Related Question