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Interactive Plotting

Example — Selecting Plotting Points from the Screen

You can interact with graphs or generate x-y coordinates interactively. The ginput function enables you to use the mouse or the arrow keys to select points to plot. ginput returns the coordinates of the pointer's position, either the current position or the position when a mouse button or key is pressed. For more information see the ginput function. You can use it to pick points on a graph to return their x and y values for processing, to outline an area of interest, or to draw arbitrary shapes.

This example illustrates the use of ginput with the spline function to create a curve by interpolating in two dimensions.

First, select a sequence of points, [x,y], in the plane with ginput. Then pass two one-dimensional splines through the points, evaluating them with a spacing one-tenth of the original spacing:

axis([0 10 0 10])
hold on
% Initially, the list of points is empty.
xy = [];
n = 0;
% Loop, picking up the points.
disp('Left mouse button picks points.')
disp('Right mouse button picks last point.')
but = 1;
while but == 1
    [xi,yi,but] = ginput(1);
    plot(xi,yi,'ro')
    n = n+1;
    xy(:,n) = [xi;yi];
end
% Interpolate with a spline curve and finer spacing.
t = 1:n;
ts = 1: 0.1: n;
xys = spline(t,xy,ts);

% Plot the interpolated curve.
plot(xys(1,:),xys(2,:),'b-');
hold off

This plot shows some typical output:

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Contour Plots

Animation

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