We will demonstrate the power of the new database by starting with a regional hemisphere map centered near Papua New Guinea and zoom in on a specified point. The map regions will be specified in projected km from the projection center, e.g., we may want the map to go from -2000 km to +2000 km in the longitudinal direction and -1500 km to +1500 km in the latitudinal direction. However, GMT programs expects degrees in the -R option that specifies the desired region. Given the chosen map projection we can automate this process by using a simple cshell script that we call getbox:
range=`(echo $2 $4; echo $3 $5) | mapproject $1 -R0/360/-90/90 -I -Fk -C`
echo $range | awk '{printf "-R%f/%f/%f/%fr\n",$1,$2,$3,$4}'
Also, as we zoom in on the projection center we want to draw the outline of the next map region on the plot. To do that we need the geographical coordinates of the four corners of the region rectangle. Again, we automate this task by adding the simple script getrect:
(echo $2 $4; echo $3 $4; echo $3 $5; echo $2 $5) | mapproject $1 -R0/360/-90/90 -I -Fk -C