Basics of MATLAB and Beyond

The conclusion is that most viewers find it very difficult to interpretthese sorts of images; the cognitive switch from, for example, roygbivto amplitude is very slow and nonintuitive. A way out of this isto use a palette of slightly varying, nonsaturated colours. These sortsof colours have been used to create high-quality geographic maps formany years. Most of matlab’s colour maps consist of highly saturatedcolours (including the default colour map, which is jet(64)). It is betterto forgo these sorts of colour maps and stick with the calmer onessuch as gray, bone, orsummer. The gray colour map has the addedadvantage that printed versions will reproduce easily, for example, on aphotocopier. 2 The companion m-files include some other colour maps:redblue, myjet, yellow, green, red, and blue.To distinguish adjacent patches of subtly different colours, the eyecan be helped by enclosing the patches with a thin dark edge. Thecontourf function, therefore, is an excellent way of displaying this sortof data. 37.5 Extracting Logical DomainsLet us look again at the peaks function:[x,y,z] = peaks;surfl(x,y,z)axis tightcolormap(gray(64))Suppose we want to extract the part of this surface for which the z valueslie between 2 and 4. We use exactly the same technique as was givenon page 23. The find command is used first to find the indices of the zvalues that satisfy the logical test:>> ind = find(2 size(ind)ans =234 1There are 234 elements in z that satisfy our condition. We can plot theseelements over the surface as follows:2 Edward R. Tufte, Visual Explanations (Graphics Press, Cheshire Connecticut,1997), pp. 76–77.3 Edward R. Tufte, Envisioning Information (Graphics Press, Cheshire Connecticut,1990), pp. 88ff.c○ 2000 by CRC Press LLC