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68 CHAPTER 8. SURFACE AND CONTOUR PLOTSinclude "contour.gle"begin contourdata "saddle.z"values 0.5 1 1.5 2 3end contourbegin graphtitle "Saddle Plot Contour Lines"data "saddle-cdata.dat"d1 line color blueend graphcontour_labels "saddle-clabels.dat" "fix 1"The contour block can contain the following commands:data file$Specifies the name of the .z file.values v 1 , . . . , v nSpecifies the z-values to contour at.201510500.51.00.50.5Saddle Plot Contour Lines1.5 2.01.52.0 3.01.01.5 3.02.01.00 2 4 6 8 10values from v 1 to v n step sSpecifies the z-values to contour at by means of from/to/step.smooth integerSpecifies the smoothing parameter.The contour block creates the files “data-clabels.dat” and “data-cdata.dat” with the prefix “data” thename of the .z file. The file “data-clabels.dat” contains information for drawing labels on the contourplot. This is done by the subroutine contour labels defined in the library “contour.gle” in the exampleabove. The file “data-cdata.dat” contains the (x, y) values of the contour lines. This file can be used asinput to a graph block and plotted with the “d1 line” command as shown in the example above.8.5 Color MapsColor maps plot a function z = f(x, y) by mapping z to a color range. The following example combinesa color map with a contour plot.begin contourdata "volcano.z"values from 130 to 190 step 10end contourbegin graphtitle "Auckland’s Maunga Whau Volcano"data "volcano-cdata.dat"xaxis min 0 max 20yaxis min 0 max 20d1 line color blackcolormap "volcano.z" 100 100end graphAuckland’s Maunga Whau Volcano201816141210864200 2 4 6 8 10 12 14 16 18 20The options to the colormap command are as follows:colormap fct pixels-x pixels-y [color] [invert] [zmin z 1 ] [zmax z 2 ] [palette pal]• fct specifies the function to map. This can either be the name of a .z file, or it can be a functiondefinition f(x, y).