# (35) Spherical triangulation and distance calculations

The script produces the plot in Figure. Here we demonstrate how sphtriangulate and sphdistance are used to compute the Delauney and Voronoi information on a sphere, using a decimated GSHHG crude coastline. We show a color image of the distances, highlighted with 500-km contours, and overlay the Voronoi polygons in green. Finally, the continents are placed on top.

    #!/usr/bin/env bash
    #               GMT EXAMPLE 35
    #
    # Purpose:      Illustrate sphtriangulate and sphdistance with GSHHG crude data
    # GMT modules:  coast, plot, makecpt, grdimage, grdcontour, sphtriangulate, sphdistance
    # Unix progs:   rm
    #

    # set AWK to awk if undefined
    AWK=${AWK:-awk}

    gmt begin ex35
    	# Get the crude GSHHS data, select GMT format, and decimate to ~20%:
    	# gshhs $GMTHOME/src/coast/gshhs/gshhs_c.b | $AWK '{if ($1 == ">" || NR%5 == 0) print $0}' > gshhs_c.txt
    	# Get Voronoi polygons
    	gmt sphtriangulate @gshhs_c.txt -Qv -D > tt.pol
    	# Compute distances in km
    	gmt sphdistance -Rg -I1 -Qtt.pol -Gtt.nc -Lk
    	gmt makecpt -Chot -T0/3500
    	# Make a basic image plot and overlay contours, Voronoi polygons and coastlines
    	gmt grdimage tt.nc -JG-140/30/18c
    	gmt grdcontour tt.nc -C500 -A1000+f10p,Helvetica,white -L500 -GL0/90/203/-10,175/60/170/-30,-50/30/220/-5 -Wa0.75p,white -Wc0.25p,white
    	gmt plot tt.pol -W0.25p,green,.
    	gmt coast -W1p -Gsteelblue -A0/1/1 -B30g30 -B+t"Distances from GSHHG crude coastlines"
    	# cleanup
    	rm -f tt.pol tt.nc
    gmt end show

Spherical triangulation and distance calculations