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Perhaps the best way to think about object movies is as a set of individual views taken from a the surface of an invisible sphere which surrounds an object. Imagine a consistent coordinate system of points evenly spaced apart around the surface of the sphere similar to the graphic below.
Uniform spacing of points around a sphere
| Although this graphic shows images being captured with a video camera, in reality any type of camera can be used to capture source images for objects. |
At each junction of coordinates on the surface of the sphere, an image is captured of the object. The vertical position, or tilt, looking directly down on the object would have a 90 degrees vertical angle, while the vertical position looking directly up at the object from below would be a -90 degrees vertical angle. The mid-point vertically (i.e., the equator) would be 0 degrees.
Similarly, at each of the vertical angle positions (tilts) from 90 degrees to -90 degrees, you can imagine a similar sequence of horizontal positions (pans) which would range from 0 degrees to 360 degrees as you progressed around the sphere.
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| The number of degrees between each of the vertical and horizontal angles is up to you as the developer. It is only recommended that you space both horizontal and vertical angles the same amount. Thus, if you capture images every 15 degrees vertically, you should also capture images every 15 degrees horizontally. This helps ensure that the resulting QTVR object movie has a consistent responsiveness to cursor movement and changes from view to view in any direction in a uniform manner. |
A smaller space between horizontal and vertical angles implies that more shots will be required to complete the movie. For example, it would take a total of 684 individual images to represent a full 360 degrees horizontal and 90 degrees to -90 degrees vertical view of an object if shots are taken every 10 degrees (36 horizontal shots at each of the 19 vertical angles). In contrast, it would take 2,664 shots to represent the same object if shots were taken every 5 degrees (72 horizontal shots at each of the 37 vertical angles). Or, it would take only 234 images if shots were taken every 15 degrees.
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| In general, 10 degrees spacings between angles in both horizontal and vertical directions provide a fairly smooth sense of rotation and is a good balance of file size versus smoothness of rotation. Since the number of images to capture has a direct relationship to the final size of the object movie, though, you should experiment with different degree increments for your initial object movies until you get a feel for the file sizes which result. |
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