function readnextkey, unit
	s=''
	lat=0.
	lon=0.
	startyr=0
	
	if eof(unit) then return, -1
	readf, unit, s
	data = strsplit(s,/extract)
	
	if n_elements(data) ne 4 then return, -1
	fname=data[0]
	reads, data[1],lat
	reads, data[2],lon
	reads, data[3],startyr

	result= {name: 'wthdat', wth:fname,lat:lat/100, lon:lon/100,startyr:startyr}
	return, result
end