计算机视课件8.pptVIP

Course 8 Contours * * Course 8 Contours Def: edge list ---- ordered set of edge point or fragments. Def: contour ---- an edge list or expression that is used to represent the curve. A contour can be open or closed. Digital Curve. (1) Curve length: (2) K-slope: the (angle) direction vector between points with k edge points apart. (3) K-curvature: the difference between left k-slope and right k-slope at a digital curve point: 2. Curve Representations 1) Chain code Chain code quantities a space to 8 directions and encodes a contour at each edge point with the directions in an ordered sequence. ------- Chain code has compact description. ------- Chain code cannot express branched curves. plot: For a digital curve, compute curve length and slope from a beginning edge point. Then plot the obtained curve length and slop in space. ------ Line segment in curve; horizontal line in plot. ------ Circular arc in curve; line segment of some direction in space. ------ Using plot can easily segment a curve at discontinuous point of plot. Graph representation: Establish topology relations among edge list points. Each edge point is a graph node. Struct Node { int node_number; int curve_number; int x, y; // position char type; int link[8]; //link relation int link_direction[8]; //heading or ending char flag; //process flag } node; ------ Digital description of curve. ------ Can handle branched curves. ------ Easy in operation. ------ Use more memories, but it can be simplified. e.g. to remove nodes that have type=2. Struct link { int curve_number; int link_length; int node_list[]; char flag; //process flag } link; 3. Polyline re