BITMAP plots a land area by testing each point of the area using LNDSEA. The plotting area is segmented into (nx X ny) regions. Each point is tested for the presence of land/sea. For each resolutoin line of latitude, a horizontal line is drawn through all points that are land (or sea as desired). A linear projection is used. The latitude and longitude are assumed to be a linear grid on a flat surface. This routine will plot the entire map surface. Use of the PLOT routine clipping option will permit plotting only limited of the map surface if desired. The transformation of a latitude/longitude pair (a,b) in degrees to an (x,y) pair for plotting is:
x = (b - s) * along / 360
y = (a + 90) * alat / 180
CALL BITMAP(s,alat,along,nx,ny,i)
s (R): longitude of left-mode edge of map (-180 to +180)
alat,along (R): latitude, longitude axis length (plot units)
nx,ny (I): x,y resolution specified as the number of lat/longs
to test for land/sea
i (I): plot flag
= 0 plot land area
= 1 plot sea area