Object space algorithm: Back-Face removal. · No faces on the back of the object are displayed. · In general – about half of objects faces are back faces. Computer Graphics Lecture 8 Hidden Surface Removal Taku Komura 1 1 Or if N.V > 0 we are viewing the back face so polygon is obscured. . Tree construction and traversal (object-space ordering algorithm – good for relatively few static. Occluded surfaces: hidden surface removal (visibility). ▫ Back faces: back face culling. ▫ Faces OpenGL): Z-buffer (or depth buffer) algorithm. ▫ Requires lots .

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Build the left and right subtrees recursively. If any of the following tests is positive, then we can assume P can be drawn before Q. When projecting surfaces, check for intersections. Add subsequent edges based on whether they are inside or outside. Spatial Sorting Chung Ji Hye. Calculating Normal using plane equations. The main disadvantage of ray casting is that the method is slow. Share buttons are a little bit lower. Split any polygons lying on both sides of the root see below.

Engineering in your pocket Download our mobile app and study on-the-go. For each projected x, y pixel position of a polygon, calculate depth z. By examining parameter C for the different planes defining an object, we can immediately identify all the back faces.


Surfaces can be processed in any order. There are four possible relationships that a surface can have with a specified area boundary. Removval polygon is on edge — either can be used.

When we want to display a 3D object on a 2D screen, we need to identify those parts of a screen that are visible from a chosen viewing position.

Visible Surface Detection

The depth values for a pixel are compared and the closest smallest z surface determines the color to be displayed in the frame buffer. Cokputer three points in space x1 ,y1,z1x2,y2,z2x3,y3,z3 the equation of the plane through these points is given by. It is an image-space approach.

Normal to the algirithm is the vector A ,B,C. Back face culling View-frustrum culling Detail culling Occlusion culling. Ray casting is a brute force technique that makes no use of pixel coherence. Let us take the polygon P at the end of the list. Explain Back – Face Removal Algorithm. Before drawing P, we make the following tests. This method is developed by Cutmull.

Back Face Removal

Begin with a ggaphics of linear equations, for example, a system involving three variables. Choose a polygon from each side — split scene again.

Right Handed coordinate System. There are two other matrices obtained by replacing the coefficients in each column by the constants c 1 and c 2 respectively.

Download ppt “Hidden Surface Removal”.

Computer Graphics Visible Surface Detection

You get question papers, syllabus, subject analysis, answers – all in one app. To use this website, you must agree to our Privacy Policyincluding cookie policy. Memory for z-buffer is now not expensive Diversity of primitives — not just polygons.


If eye is in rear half-space for a polygon can back face cull. When object description is converted to projection coordinates x,y,z gra;hics pixel position on the baciface plane is remobal by x and y coordinate and z value gives the depth information. Can be used to generate correct visibility for arbitrary views. Two important tables, edge table and polygon table, are maintained for this.

For a perspective projection, we must determine if the Center of Projection COP is inside or outside of the planes of the polygons of the object. Ray casting is easy to implement for polygonal models because the only calculation required is the intersection of a line compputer a plane. The identification and removal of these surfaces is called Hidden-surface problem. As shown in figure cwe will first process the node B.

Many slides adapted from Amitabh. Edges that span the extension of an edge that is already in the tree are split into two and both are added to the tree. The new cut grxphics are inserting into the depth order and the process continues. For a perspective projection, it is a little more complicated. Download our mobile app and study on-the-go.