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POAssociate (.assoc) binary file structure / probing unknown file structure
 

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  1. POAssociate (.assoc) binary file structure / probing unknown file structure
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    <p>I have a file that has a .assoc ending, and is apparently a 'binary associated file', though I can find no information on files of that sort online. It is read by fortran and idl, is 49Mb, and I'm trying to read it into python. This is probably too much of an open question, but could anyone suggest a way to probe the file's structure to get some idea of how I could read it?</p> <p>I know that the file is a map, presumably 2D, of elevations on Mars. And it has a short ascii header:</p> <pre><code> 7200 3600 MOLA .05 dg/px topo 5/2002 --------------------------------------------------------- header length 14400 bytes map X size 7200 map Y size 3600 no-data value 30303 maximum value 21197 minimum value -8204 The map is stored as an INT array with X as longitude and Y as latitude. The map is assumed to be global in coverage. --------------------------------------------------------- </code></pre> <p>Sorry for the ill-formed question, but general advice on how to probe an unknown file type would be much appreciated. Or if you know of this file type then that would be even better!</p> <p>Here is a snippet of the idl code that reads the file:</p> <pre><code>ELMAP='elevmap.assoc' OPENR, ELUN, ELMAP, /GET_LUN B = ASSOC(ELUN,BYTARR(100)) ; assoc header HEADER = STRING(B[0]) ; read the header NLON = 0 ; 'fix' no. of longitudes NLAT = 0 ; 'fix' no. of latitudes READS,HEADER,NLON,NLAT ; read no. of lons/lats EXG = NLON/360 ; longitude scale (pix/deg) EYG = NLAT/180 ; latitude scale (pix/deg) EMAP = ASSOC(ELUN,INTARR(1),14400) </code></pre> <p>A hexdump of the first 30 bytes (I did "od -H -N 30 elevmap.assoc") looks like this:</p> <pre><code>0000000 20202020 20202020 30303237 20202020 0000020 20202020 30363320 4f4d2030 0000414c 0000036 </code></pre> <p>A hexdump of the first 30 bytes after the header ("od -H -j 14400 -N 30 elevmap.assoc", please let me know if I'm misunderstanding this) looks like this:</p> <pre><code>0034100 0e970e93 0ea50e9d 0ea50ea5 0ea50ea5 0034120 0ea50ea5 0ea40ea4 0ea20ea3 00000ea2 0034136 </code></pre>
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    1. COCould you do a `ls -l` and tell us the total filesize?
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    2. COHave you tried looking at it with a hex editor? Do you the IDL or Fortran source code that reads it?
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    3. COIt's 49Mb. I haven't got the Fortran source code that reads it, I've added to my original question the idl code that reads it. I hadn't tried a hex editor, I'll look in to that. Thanks.
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