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Re: opening and display large file


"r.bauer" wrote:

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

Hi Sylvain,

Instead of OPEN / CLOSE you can use ASSOC too.

The idea is to display portions of the large image in a loop.
e.g. 480x600

I hope this helps a bit.


Thanks for all your answer everybody
I hope this could help but I know this online help exemple since I've pass more than a week trying to decipher it. Of course, giving exemple with 512 x 512 images that have nothing to do with the usual size you'll find in the remote sensing, astronomy and medical field doesnt really help. I wont say what I think of the documentation just to stay polite... The best way to learn a langage is trough looking at sample code as long that sample code present some real life problem solving. How about handling a 24,000 x 48,000 avhrr mosaic with more than 3 channels plus surface (GTOPO30 merged with USGS dem) plus vector "drapping"(vmap)(retesselating the surface with constrain) to export in segmented multi-scale vrml IndexedFaceSet - that's the real life job I have to do.

Give me an open file to work with, and I know what to do after. I sell my piano to buy IDL naively thinking that it was handling large file ( well, RSI claim they have "industrial strenght" tool to handle very large stuff ). Where are those functionality?
Do I need to write my own image manager? Should I have buy ErMapper instead?
Here I dont have much clue; opening the file in a kind of ram disk? Along IDL procedure and functions, which one should be used to implement this?
So please anybody, any cue especially pointer to sample code that does a little something signifiant will be tremendiously appreciated.

I still need help to understand why my usgs dem code doest work - see other post; why a statement which execute fine from the console, doest work anymore inside a loop? I know, its me but where?

Sylvain Carette
VRML designer-composer

The online help says.


Result = ASSOC( Unit, Array_Structure [, Offset] [, /PACKED] )


Suppose that the file images.dat holds 5 images as 256-element by
256-element arrays of bytes. Open the file for reading and create an
associated variable by entering:

OPENR, 1, 'images.dat' ;Open the file as file unit 1.

A = ASSOC(1, BYTARR(256, 256)) ;Make an associated variable.