Hot to locate indices of 2-D data located out of circle?

Dear All,

I have x,y data that are extracted from a triangle solution. I wonder if there is a command (no loop) that will find the indices of elements when x^2+y^2 > than a specific value. The reason I want to eliminate them.

Thank you

Aziz

Answer 1

[Walter Roberson]

vector_of_y_values = (1:number_of_rows) - y_center;
vector_of_x_values = (1:number_of_columns) - x_center;
[Yg, Xg] = ndgrid(vector_of_y_values, vector_of_x_values);
idx = find(Xg.^2 + Yg.^2 > specific_value);

[Abdulaziz Abutunis]

Hi Walter,

Thank you for the suggestion.

This command ini the last line will give all the possibilities of any xg and yg that meet the condition of > specific_value. However, the xg and yg should be a coordinate of a point at a specific location.

Lines of code:

percentage_added=R+(R*1.5);

[Yg, Xg] = ndgrid((1:length(y)), (1:length(x)));

ind_remove = find(Xg.^2 + Yg.^2 > R*percentage_added);

ind_remove was larger than the arrays of x and y

The next steps were to plot the z at these coordinates:

z(ind_remove)=[];

x(ind_remove)=[];

y(ind_remove)=[];

dt = delaunayTriangulation(x,y) ;

tri = dt.ConnectivityList ;

xi = dt.Points(:,1) ;

yi = dt.Points(:,2)

F = scatteredInterpolant(x,y,z);

zi = F(xi,yi) ;

trisurf(tri,xi,zi,yi)

Any further suggestion is highly appreciated

Aziz

[Abdulaziz Abutunis]

I have not used the ndgrid and used the next line. Also, I made a mathematical mistake in the previous script by forgetting the square root

ind_remove = find(sqrt(x.^2 + y.^2) > percentage_added);

Though your answer will do what i want if not using the ndgrid

Thanks

[Walter Roberson]

I forgot to account for possible scale factors such as the possibility that the x coordinates are percentage. The x and y vectors should be constructed so that they list the x and y coordinates, such

linspace(firstx, lastx, number of x)

[Abdulaziz Abutunis]

Thank you, Walter, for your valuable suggestions