Dollying the Camera

Summary of Techniques

In the camera metaphor, a dolly is a stage that enables movement of the camera from side to side with respect to the scene. The camdolly command implements similar behavior by moving both the position of the camera and the position of the camera target in unison (or just the camera position if you so desire).

This example illustrates how to use camdolly to explore different regions of an image. It shows how to use the following functions:

  • ginput to obtain the coordinates of locations on the image

  • The camdolly data coordinates option to move the camera and target to the new position based on coordinates obtained from ginput

  • camva to zoom in and to fix the camera view angle, which is otherwise under automatic control

Implementation

First load the Cape Cod image and zoom in by setting the camera view angle (using camva).

load cape
image(X)
colormap(map)
axis image
camva(camva/2.5)

Then use ginput to select the x- and y-coordinates of the camera target and camera position.

while 1
  [x,y] = ginput(1);
  if ~strcmp(get(gcf,'SelectionType'),'normal')
    break
  end
  ct = camtarget;
  dx = x - ct(1);
  dy = y - ct(2);
  camdolly(dx,dy,ct(3),'movetarget','data')
  drawnow
end
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