| Re: opening and display large file [message #21559 is a reply to message #21548] |
Wed, 30 August 2000 00:00   |
Sylvain Carette
Messages: 19
Registered: May 2000
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Junior Member |
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<p><tt>"r.bauer" wrote:</tt>
<blockquote TYPE=CITE><tt>Sylvain Carette wrote:</tt>
<br><tt>></tt>
<br><tt>> Hi</tt>
<br><tt>> How do you manage to display very large images? What is the options?</tt>
<br><tt>> From the manual, it seem that using "assoc" is a winner but maybe
with</tt>
<br><tt>> one little example it would be more clear how can this be (It
seem to</tt>
<br><tt>> me that it is an important aspect of programming with IDL since
most</tt>
<br><tt>> of the time you'll deal with larger than memory files).</tt>
<br><tt>> Even with assoc, dont you still have to copy from the file to
an array</tt>
<br><tt>> before display?</tt>
<br><tt>> I dont decipher exactly why and when to use readu or read_binary,
the</tt>
<br><tt>> file pointer, assoc or writing to an offscreen buffer.</tt>
<br><tt>></tt>
<br><tt>> I tried to open and display a GTOPO30 tile (4800 x 6000 int).
tv could</tt>
<br><tt>> not display it - froze. I tried "slide_image" but it didnt scroll
with</tt>
<br><tt>> "retain=1" while "retain=2" and "retain=3" result in windows
error and</tt>
<br><tt>> crash.</tt>
<br><tt>></tt>
<br><tt>> Since most of my data fall in the 30mb to 610 mb range, I need</tt>
<br><tt>> absolutely to open and display very large file. What is available?</tt>
<br><tt>> Pointers, sample code, library, ideas, etc, I'm listening....
Just</tt>
<br><tt>> knowing that it have to be handled on your own or that IDL provide</tt>
<br><tt>> facility (that they forgot to explain in the manual) to deal
with this</tt>
<br><tt>> will already be invaluable</tt>
<br><tt>></tt>
<br><tt>> Thanks</tt>
<br><tt>></tt>
<br><tt>> Sylvain Carette</tt>
<br><tt>> VRML designer-composer</tt>
<br><tt>></tt><tt></tt>
<p><tt>Hi Sylvain,</tt><tt></tt>
<p><tt>Instead of OPEN / CLOSE you can use ASSOC too.</tt><tt></tt>
<p><tt>The idea is to display portions of the large image in a loop.</tt>
<br><tt>e.g. 480x600</tt><tt></tt>
<p><tt>I hope this helps a bit.</tt><tt></tt>
<p><tt>Reimar</tt>
<br><tt></tt> </blockquote>
<tt>Thanks for all your answer everybody</tt>
<br><tt>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.</tt><tt></tt>
<p><tt>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?</tt>
<br><tt>Do I need to write my own image manager? Should I have buy ErMapper
instead?</tt>
<br><tt>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?</tt>
<br><tt>So please anybody, any cue especially pointer to sample code that
does a little something signifiant will be tremendiously appreciated.</tt><tt></tt>
<p><tt>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?</tt><tt></tt>
<p><tt>Sylvain Carette</tt>
<br><tt>VRML designer-composer</tt>
<br><tt></tt>
<blockquote TYPE=CITE><tt></tt>
<br><tt>The online help says.</tt><tt></tt>
<p><tt>Syntax</tt><tt></tt>
<p><tt>Result = ASSOC( Unit, Array_Structure [, Offset] [, /PACKED] )</tt><tt></tt>
<p><tt>Example</tt><tt></tt>
<p><tt>Suppose that the file images.dat holds 5 images as 256-element by</tt>
<br><tt>256-element arrays of bytes. Open the file for reading and create
an</tt>
<br><tt>associated variable by entering:</tt><tt></tt>
<p><tt>OPENR, 1, 'images.dat' ;Open the file as file unit 1.</tt><tt></tt>
<p><tt>A = ASSOC(1, BYTARR(256, 256)) ;Make an associated variable.</tt></blockquote>
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