| Re: Coding for speed help needed [message #9054] |
Fri, 30 May 1997 00:00  |
Liam Gumley
Messages: 473
Registered: November 1994
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Senior Member |
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Patrick V. Ford wrote:
> pop_size = 36; this can vary greatly
> dim = 64
> B = bytarr( dim * dim * 5 * pop_size)
> There are pop_size individuals
> The first 64*64 (dim*dim) bytes code for the activity or intensity in a 64
> by 64 image. The next 4*64*64 bytes code for the attenuation coefficients
> which are
> between 0.0 and 1.0, where 1.0 is no attenuation and 0.0 is 100%.
Patrick,
Are you familiar with structures in IDL? Any time you have to read mixed
datatypes from a datafile, structures are usually the easiest way to do
it. For example, let's say that on disk you have (in one contiguous
file),
- a byte array of size 64x64
- a float array of size 64x64
then to read it, you would do something like this:
openr, lun, 'input.dat', /get_lun
data = { array1 : bytarr( 64, 64 ), array2 : fltarr( 64, 64 ) } ;
structure definition
readu, lun, data ; read the structure from disk
free_lun, lun
print, data.array1( *, 0 ) ; print the first 64 elements of the byte
array
print, data.array2( *, 0 ) ; print the first 64 elements of the float
array
Then if you need to swap byte order, all you have to do is
data = swap_endian( data )
which will take care of all the data types in the structure.
Cheers,
Liam.
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