Basics of MATLAB and Beyond

diagram. Such a triangular grid can be calculatedfor our seamount example of the last section. Thetriangles are defined using the delaunay function:3>> tri = delaunay(x,y);>> tri(563:end,:)ans =2 4 71 2 68 1125 245 59We have displayed the last few lines of the M × 3 matrix tri, whichdefines the triangles by a set of triplets that are indices into the x and yvectors. For example, the four triangles we have displayed in ans are〈( ) ( ) ( )〉1: x(2),y(2) x(4),y(4) x(7),y(7)〈( ) ( ) ( )〉2: x(1),y(1) x(2),y(2) x(6),y(6)〈( ) ( ) ( )〉3: x(8),y(8) x(3),y(3) x(11),y(11)〈( ) ( ) ( )〉4: x(25),y(25) x(245),y(245) x(59),y(59)We can use this triangulation matrix to plot a surface of the seamountdata; each face of the surface is one of the triangles:trisurf(tri,x,y,z)hold onplot3(x,y,z,’o’)axis tightThe functions trisurf and trimesh do not create surface objects;rather, they create patch objects.37 Three-dimensional Modelling37.1 PatchesIn this section we discuss the representation of real-world objects. Suchobjects are built up using their faces (the six faces of a cube, for example).In matlab “faces” are patches, and are defined using the patchcommand. Patches are blobs of coloured light (or ink) that are defined byvertex points. The line between the vertices is the patch’s edge and theenclosed area is the patch’s face. Before talking about three-dimensionalobjects we discuss the simpler two-dimensional patch.c○ 2000 by CRC Press LLC