Introduction of Visible Surface Detection
- For displaying a realistic presentation of the given 3Dimentional object, hidden surfaces and hidden lines should be identified for remove.
- The process of considering and eliminating of these hidden surfaces is termed as the visible-line/surface determination or it may be hidden-line/surface elimination.
- To build a realistic view of the specified 3Dimentional object, it is essential to find out that lines or surfaces of the objects are visible. For this, we necessitate to conduct visibility tests.
- Visibility tests are organized to find out the surface that is visible from a specified viewpoint.
- There are two basic approaches for visible-surface determination, as per to whether they deal along with their projected images or along with object descriptions directly. These two approaches are termed as image-space approach and object-space approach, correspondingly.
- Object space methods are applied in the physical coordinate system wherein objects are explained whereas image space methods are applied in screen coordinate system wherein the objects are viewed.
- Image-space approach needs examining all the objects in the scene to find out such is closest to the viewer beside the projector passing by the pixel. The visibility is selected point by point at each pixel position upon the projection plane. If various objects are 'n' and the pixels is 'p' after that effort is proportional to n.p.
- Object-space approach compares each object directly along with each other inside the scene definition and eliminates those objects or portion of objects such are not visible.
- Object-space approach compares all of the n objects to itself and to another object, discarding invisible portions. Hence the computational effort is proportional to n2.
- According to this category of Image space approach, we have two methods as:
A) Z-buffer method and
B) Scan-line method.
- In between all the algorithms for visible surface determination, the Z-buffer is maybe the easiest, and is the most extensively used method.
- Z-buffer method finds the visible surfaces through comparing surface depths as z-values at all pixel positions on the projection plane.