Part 2: Reducing level of detail

Frequently, the objects are placed at various distances from the observer. The object is distant, thus resulting in a smaller image. This can be used, to calculate the lower level of detail and object display much faster to a lesser degree of detail. The whole situation is illustrated in figures.

Showing different levels of detail

Left object is displayed in maximum detail and to the right level of detail is reduced to a minimum. This object is named "Stanford Bunny", was acquired 3rd scanner and contains a large number of triangles. Therefore, it is often used to demonstrate and test the quality of algorithms for simplifying models.

polygon reducer lod

The second image shows the use of multiple levels of detail in one scene. The nearest object is displayed in the maximum degree of detail, which decreases with distance from the observer. Minor detail of the object at the rear is not perceivable, even though it is composed of a much smaller number of triangles. The advantage of the object in smallest degree of detail is that it contains 1000 times lesser count of triangles than the original object, and will be approximately 1000 times quickly drawn on the screen.

polygon reducer lod scene

Currently, there are several types of techniques which are aimed at different types of objects. Here are some methods for simplifying the curves, elevation fields, etc. The biggest attention, however, receives a simplified techniques objects represented by irregular polygonal surfaces. On the one hand, algorithms, which work very quickly, but produce inferior quality results, on the other, then very well aproximující algorithms, which are in turn very slow. It is always necessary to accede to a compromise between speed and quality of production approximations.

If the scene contains 100 objects "Standfor bunny", it would not be rendered in real time, because it contains 7 million triangles. But if the scene appears the 5 nearest object in full detail, 20 other objects in a bit smaller degree of detail, 25 objects still in a smaller detail, and 50 in the smallest degree of detail, you will need to render only 400 thousand triangles, which is 5% of the original quantity and the scene has displayed most of today's computers in real time.

Vyšlo 11.08.2008, v blogu: (printer friendly version)


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