How do determine the maximum and minimum point form origin on a contour graph

I have created a contour graph from the folloing code, where C_100030_alt173 is my raw data. I will return a contour plot with points containing (x, y, level). How do I find the max. and min. point from the origin (0,0). ie. how do i extract xy values for all points and do a simple (x^2+y^2)^1/2 calculation and identify the max. and min.

Thank you so much

x=(-1:1/512:1);

C_100030_alt173
c1P5_alt173=reshape(CON,[1025,1025]);
a=[0,0];

v1=[0.5,0.5];
v2=[0.11,0.11];
contour(x,x,c1P5_alt173,v1,EdgeColor="black");
hold on
contour(x,x,c1P5_alt173,v2,EdgeColor="blue");

Answer 1

[Aquatris]

Not sure exactly what you want but contour function can give you interpolated x-y positions for a specific level. From there you can use a simple calculation to find the max distance to origin for that spefic level.

Z = peaks;

% get x-y locations of points corresponding to desiredLevel
desiredLevel = 1.949;
p = contourc(Z,desiredLevel*[1 1]); 
% remove x y positions outside of [0 50] range
p(:,p(1,:)>50|p(2,:)>50) = [];
% get max distance
dist = sqrt(p(1,:).^2+p(2,:).^2);
maxDistIdx = find(dist==max(dist));

% draw contour graph
[M,c] = contourf(Z);xlim([0 50]);ylim([0 50])
hold on
% draw each point for the desiredLevel and the largest distance for that level
plot(p(1,:),p(2,:),'rx',...
   [0 p(1,maxDistIdx)],[0 p(2,maxDistIdx)],'r-','LineWidth',2)
hold off

[Chieh-Yen]

Thank you for the answering the question

As the below plot, each point on the graph has a X and Y value. I would like to extract all the xy values to calculate the min and max distance from (0,0)

[Aquatris]

If you only want x-y values for the blue and black line, you can call the countourc() function with their respective levels (for blue it seems like 0.1154). This will give you not every x-y points since there are infinite number of x-y values on those curves, but will give you sufficiently high number of x-y points.

[Chieh-Yen]

Just a small question, say my raw data is arranged into a 1025*1025 matrix as c1P5_alt173, how do I formulate the contourc() to aquire all levels, or say limit the level range from 0<level<1. Thank you a lot

p = contourc(x,x,c1P5_alt173); 

[Aquatris]

This should work for you;

levelRange = [0 1];
p = contourc(x,x,c1P5_alt173,levelRange);

However I do not think using the 'x' variable for both X and Y axis is correct. Dont you have seperate 'y' array as well?

[Chieh-Yen]

no i don't have a y array, the plot is created through the following commend

contour(x,x,c1P5_alt173,v1,EdgeColor="black");

[Aquatris]

Then still

p = contourc(x,x,c1P5_alt173,levelRange);

would work for you.

You can read more and see more examples on the countourc function here.

[Chieh-Yen]

thank you very much for all the explanation.