O.3.3 Prescribed label placements

Here, we specify four points where we would like contour labels to be placed. Our points are not exactly on the contour lines so we give a nonzero ``slop'' to be used in the distance calculations: The point on the contour closest to our fixed points and within the given maximum distance will host the label.

cat << EOF > fix.d
80      -8.5
55      -7.5
102     0
130     10.5
EOF
pscoast -R50/160/-15/15 -JM5.5i -Glightgray -A500 -K -P > GMT_App_O_3.ps
grdcontour geoid.grd -J -O -B20f10WSne -C10 -A20+d+s8 -Gffix.d/0.1i -S10 -T:LH >> GMT_App_O_3.ps

The angle of the label is evaluated from the contour line geometry, and the final result is shown in Figure O.3.

Figure: Four labels are positioned on the points along the contours that are closest to the locations given in the file fix.d in the -Gf option.

To aid in understanding the algorithm we chose to specify ``debug'' mode (+d) which placed a small circle at each of the fixed points.