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M. Of colors and color legends - web.mst.edusgao/GMT-manual/GMT_Docs_Part111.pdf · APPENDIX M. OF COLORS AND COLOR LEGENDS 205 M.2 Labeled and non-equidistant color legends The use

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Page 1: M. Of colors and color legends - web.mst.edusgao/GMT-manual/GMT_Docs_Part111.pdf · APPENDIX M. OF COLORS AND COLOR LEGENDS 205 M.2 Labeled and non-equidistant color legends The use

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.

Page 2: M. Of colors and color legends - web.mst.edusgao/GMT-manual/GMT_Docs_Part111.pdf · APPENDIX M. OF COLORS AND COLOR LEGENDS 205 M.2 Labeled and non-equidistant color legends The use

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.