This example will change the orientation of labels from along-track to across-track, and surrounds the labels with an opaque, outlined textbox so that the label is more readable. We choose the place the labels every 1000 km along the line and use that distance as the label. The labels are placed normal to the line:
pscoast -R50/160/-15/15 -JM5.5i -Glightgray -A500 -K -P > GMT_App_O_6.ps grdcontour geoid.grd -J -O -K -B20f10WSne -C10 -A20+d+s8 -Gl50/10S/160/10S -S10 \ -T:'-+' >> GMT_App_O_6.ps psxy -R -J -O -SqD1000k:+g+LD+an+p -W1p transect.d >> GMT_App_O_6.ps
The composite illustration in Figure O.6 shows the new effects. Note that the line connecting the extrema does not end exactly at the `-' and `+' symbols. This is because the placements of those symbols are based on the mean coordinates of the contour and not the locations of the (local or global) extrema.