usgslandcover(FILE, Wlon, Elon, Slat, Nlat)

Small function for accessing the global USGS landcover file.

This function retrieves the landcover data from the Global Land Cover Characteristics Data Base Version 2.0, specifically from the file with 30-arcsecond resolution geographic projection, i.e. the file gusgs2_0ll.img.
A lat/lon window can be specified by the user, meaning that MatLab does not have to access the entire file, thus saving memory. The function returns the landcover data, as well as matrices containing the latitude and longitude coordinates (centre-of-pixel) for each data point.