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APPENDIX M. OF COLORS AND COLOR LEGENDS 204
M. Of colors and color legends
M.1 Built-in color palette tablesFigure M.1 shows each of the 22 built-in color palettes, stored in so-called cpt tables. The programsmakecpt and grd2cpt are used to access these master cpt tables and translate/scale them to fit the user’srange of z-values. The top half of the color bars in the Figure shows the original color scale, which can beeither discrete or continuous, though some (like globe) are a mix of the two. The bottom half the color barare built by using makecpt -T-1/1/0.25, thus splitting the color scale into 8 discrete colors.
topo wysiwyg
seis split
relief sealand
rainbow red2green
panoply polar
ocean paired
nighttime no_green
hot jet
gray haxby
gebco globe
cyclic drywet
cool copper
Figure M.1: The standard 22 cpt files supported by GMT.
APPENDIX M. OF COLORS AND COLOR LEGENDS 205
M.2 Labeled and non-equidistant color legendsThe use of color legends has already been introduced in Chapter 7 (examples 2, 16, and 17). Things becomea bit more complicated when you want to label the legend with names for certain intervals (like geologicaltime periods in the example below). To accomplish that, one should add a semi-colon and the label nameat the end of a line in the cpt table and add the -L option to the psscale command that draws the colorlegend. This option also makes all intervals in the legend of equal length, even it the numerical values arenot equally spaced.
Normally, the name labels are plotted at the lower end of the intervals. But by adding a gap amount(even when zero) to the -L option, they are centered. The example below also shows how to annotate rangesusing -Li (in which case no name labels should appear in the cpt file), and how to switch the color bararound (by using a negative length).
023
66
146
200
251
299
359
416444
488
542
Neogene
Paleogene
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
Neogene
Paleogene
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
Neogene
Paleogene
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
Silurian
Ordovician
CambrianNeogene
Paleogene
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
Neogene
Paleogene
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
023
66
146
200
251
299
359
416444
488
542 0
23
66
146
200
251
299
359
416
444
488
542
0
23
66
146
200
251
299
359
416
444
488
0
23
66
146
200
251
299
359
416
444
488
0 − 23
23 − 66
66 − 146
146 − 200
200 − 251
251 − 299
299 − 359
359 − 416
416 − 444
444 − 488
488 − 542
0 − 23
23 − 66
66 − 146
146 − 200
200 − 251
251 − 299
299 − 359
359 − 416
416 − 444
444 − 488
488 − 542
Figure M.2: The many forms of color legends created by psscale.