(12) Optimal triangulation of data

Our next example operates on a data set of topographic readings non-uniformly distributed in the plane (Table 5.11 in Davis: Statistics and Data Analysis in Geology, J. Wiley). We use triangulate to perform the optimal Delaunay triangulation, then use the output to draw the resulting network. We label the node numbers as well as the node values, and call contour to make a contour map and image directly from the raw data. Thus, in this example we do not actually make grid files but still are able to contour and image the data. We use the CPT topo.cpt (created via gmtinfo and makecpt). The script becomes:

#!/usr/bin/env bash
#		GMT EXAMPLE 12
#
# Purpose:	Illustrates Delaunay triangulation of points, and contouring
# GMT modules:	makecpt, gmtinfo, contour, text, plot, triangulate, subplot
# Unix progs:	rm
#
gmt begin ex12
	# Contour the data and draw triangles using dashed pen; use "gmt gmtinfo" and "gmt makecpt" to make a
	# color palette (.cpt) file
	T=$(gmt info -T25+c2 @Table_5_11.txt)
	gmt makecpt -Cjet $T
	gmt subplot begin 2x2 -M0.1c -Fs8c/0 -SCb -SRl -R0/6.5/-0.2/6.5 -JX8c -BWSne -T"Delaunay Triangulation"
	# First draw network and label the nodes
	gmt triangulate @Table_5_11.txt -M > net.xy
	gmt plot net.xy -Wthinner -c0,0
	gmt plot @Table_5_11.txt -Sc0.3c -Gwhite -Wthinnest
	gmt text @Table_5_11.txt -F+f6p+r
	# Then draw network and print the node values
	gmt plot net.xy -Wthinner -c0,1
	gmt plot @Table_5_11.txt -Sc0.1c -Gblack
	gmt text @Table_5_11.txt -F+f6p+jLM -Gwhite -W -C1p -D6p/0i -N
	gmt contour @Table_5_11.txt -Wthin -C -Lthinnest,- -Gd3c -c1,0
	# Finally color the topography
	gmt contour @Table_5_11.txt -C -I -c1,1
	gmt subplot end
gmt end show
#
rm -f net.xy

Optimal triangulation of data.