; get lat/lon data from 1000 meter file
file = 'FY3A_MERSI_GBAL_L1_20101005_1640_1000M_MS.hdf'
hdfid = hdf_sd_start(file)
hdf_sd_varread, hdfid, 'Latitude', lat
hdf_sd_varread, hdfid, 'Longitude', lon
hdf_sd_end, hdfid

; get image data from 250 meter file
file = 'FY3A_MERSI_GBAL_L1_20101005_1640_0250M_MS.hdf'
hdfid = hdf_sd_start(file)
hdf_sd_varread, hdfid, 'EV_250_RefSB_b4', image
hdf_sd_end, hdfid

;- interpolate lat/lon arrays to 250 meter resolution
lat250 = regrid(lat, 8192, 8000)
lon250 = regrid(lon, 8192, 8000)

;- write binary files
openw, 1, 'lat250.dat' & writeu, 1, lat250 & close, 1   ; float
openw, 1, 'lon250.dat' & writeu, 1, lon250 & close, 1   ; float
openw, 1, 'image250.dat' & writeu, 1, image & close, 1  ; unsigned int