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Re: opening and display large file

This is what I use to access the GTOPO30 DEMs

 Kelly Dean

PRO ReadTopo

file = 'e:\w140n90\w140n90.dem
topo = INTarr(4800,6000)
; Open DEM, Swap_Endian if you are using a PC.
OpenR, lun, file, /Get_Lun, /swap_endian
ReadU, lun, topo
Close, lun
Free_Lun, lun
; Cut out a small area and scale it.
cut = BYTscl(topo(1500:2499,1500:2499), MIN=0 )
PRINT, ' MAX >',MAX( cut , MIN=MIN)
WINDOW, 0, XSize=1000, YSize=1000, TITLE='GTOP030'
TV, cut


Sylvain Carette wrote:

> Hi
> How do you manage to display very large images? What is the options?
> From the manual, it seem that using "assoc" is a winner but maybe with
> one little example it would be more clear how can this be (It seem to
> me that it is an important aspect of programming with IDL since most
> of the time you'll deal with larger than memory files).
> Even with assoc, dont you still have to copy from the file to an array
> before display?
> I dont decipher exactly why and when to use readu or read_binary, the
> file pointer, assoc or writing to an offscreen buffer.
> I tried to open and display a GTOPO30 tile (4800 x 6000 int). tv could
> not display it - froze. I tried "slide_image" but it didnt scroll with
> "retain=1" while "retain=2" and "retain=3" result in windows error and
> crash.
> Since most of my data fall in the 30mb to 610 mb range, I need
> absolutely to open and display very large file. What is available?
> Pointers, sample code, library, ideas, etc, I'm listening.... Just
> knowing that it have to be handled on your own or that IDL provide
> facility (that they forgot to explain in the manual) to deal with this
> will already be invaluable
> Thanks
> Sylvain Carette
> VRML designer-composer