read_smith_sandwell.py

# read a smith and sandwell image file: 
# http://topex.ucsd.edu/marine_topo/
import numpy as np

nlon=21600
nlat=17280

fin = open('topo_18.1.img','rb')
dat = np.fromfile(fin,dtype='i2')
dat.byteswap('True')
fin.close()
# mercator projection!
rad = np.pi/180.
arg2 = np.log(np.tan(rad*(45.-80.738/2.)))
inds = np.arange(nlat)+1.
arg1=rad*(nlat-inds+0.5)*1./60.
lat = 2.*np.arctan(np.exp(arg1+arg2))/rad-90.
lat = lat[::-1]
lon=np.linspace(0,360.-1./60.,nlon)+0.5/60.
dat = dat.reshape([nlat,nlon])
dat = np.flipud(dat)