pro som_block_corner_meters,filename,blocknum,somupleft,somlowright

;  this procedure calculates the meter values
;  for the SOM upper left and lower right corners
;  of the specified block in the specified file
;
;  block number is specified as a value from
;  1 to 180 (NOT 0-based)
;
;  NOTE:  shouldn't matter which grid is used,
;  the meter block corners should be at the
;  same point, so just use the first grid


fid = EOS_GD_OPEN(filename,/READ)
numgrid = EOS_GD_INQGRID(filename,gridlist)
gridnames = strsplit(gridlist,',',/EXTRACT)
gid = EOS_GD_ATTACH(fid,gridnames[0])

; get the grid dimensions and corner info for first block

status = EOS_GD_GRIDINFO(gid, xdimsize, ydimsize, hdfeos_upleft, hdfeos_lowright)

status = EOS_GD_DETACH(gid)
status = EOS_GD_CLOSE(fid)

;  get SOM corners for first block from HDF-EOS corners in file

somupleft1 = [hdfeos_upleft[0],hdfeos_lowright[1]]
somlowright1 = [hdfeos_lowright[0],hdfeos_upleft[1]]

if (blocknum eq 1) then begin
;  use first block values above
  somupleft = somupleft1
  somlowright = somlowright1
  exit
endif

minx = hdfeos_upleft[0]
maxx = hdfeos_lowright[0]
miny = hdfeos_lowright[1]
maxy = hdfeos_upleft[1]

xres = (maxx - minx)/xdimsize
yres = (maxy - miny)/ydimsize

offsets = get_offsets(filename,gridnames[0])


ulx = somupleft1[0] + (xdimsize * (blocknum-1) * xres)
uly = somupleft1[1] + (total(offsets[0:blocknum-2]) * yres)

lrx = ulx + (xdimsize * xres)
lry = uly + (ydimsize * yres)

somupleft = dblarr(2)
somlowright = dblarr(2)

somupleft[0] = ulx
somupleft[1] = uly
somlowright[0] = lrx
somlowright[1] = lry

end