Re: opening and display large file

[Sylvain Carette <sylvainc(at)total.net>]

Thanks
That's look almost what I have tryed. I'll use it "as is" to see
the difference with mine but its mostly the fact I tryed to send the whole
array to tv and slide_image.
Also, I didnt close the file and free lun immediately after reading
as you did - is this could cause memory leakage (when freezing, I was wondering
after reset if I left big lump of anaccessible memory)?
The only other difference is that instead of extracting a subset,
I used congrid to resample a lightweigth display grid. Even though, nothing
on tv and a small portion with slide_image which disapear immediately as
soon I move a scroll bar (retain=0; retain 1 & 2 just make windows
crash)...
So this mean that 4800 x 6000 is too big for those two function?
I still dont understand why it would be so big since according to the doc,
you should be able to open a file as long you have enough memory and I
have 250mb which should be enough for one gtopo tile no?

I hope I dont sound like a bugger but beleive me, I tryed to do my homework before requesting help here.
BYW, did you open usgs dem?

Sylvain Carette
VRML designer-composer

Kelly Dean wrote:

This is what I use to access the GTOPO30 DEMs

 Kelly Dean
 CSU/CIRA

================================================
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)
PRINT, ' MIN >',MIN
WINDOW, 0, XSize=1000, YSize=1000, TITLE='GTOP030'
TV, cut

END
=================================================

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
>