On 7/9/2011 2:44 AM, dpath2o wrote:
Hi Chris, et. al.
OK, so this might interest you because I don't know if it's a non-feature or
a bug in FlexFaw. Below is some code that will process the attached file.
Notice the difference in the results. However this is assuming that FlexRaw
'float' and unpack 'f' should behave in the same manner.
Your template is using 'f>' not 'f'. Do you get the
same result as readflex if you use just 'f'?
Anyway, while syntax-icly! this clunky I know that I can proceed here and
use PDL, and this makes me happy. It'd be nice to understand why these
results are different.
The '>' and '<' modifiers are for little-endian and
big-endian byte order specification.My guess is that
your platform is '<' byte order which is why you get
different results.
Cheers.
------------------------------
use strict; use warnings; use PDL; use PDL::IO::FlexRaw;
my $hdr_size=84;
my $N_DopplerBins=512;
open(CS,'dat.cs');
binmode(CS);
seek(CS,$hdr_size,0);
my $bytes = readflex( \*CS , [ { Type=>'byte' , NDims=>1 ,
Dims=>[$N_DopplerBins*4,1] } ] );
my @tmp = unpack 'f>*', ${ $bytes->get_dataref };
my $dat1 = pdl @tmp;
print "UNPACK RESULTS: ".$dat1."\n";
seek(CS,$hdr_size,0);
my $dat2 = readflex( \*CS , [ { Type=>'float' , NDims=>1 ,
Dims=>[$N_DopplerBins,1] } ] );
print "FLEXRAW RESULTS: ".$dat2."\n";
close(CS);
-------------------------------
UNPACK RESULTS: [1.963092e-12 1.4716339e-12 3.4353432e-12 2.1053842e-12
1.5967331e-12 1.3974084e-12 2.7670049e-12 ... 2.0514502e-12]
FLEXRAW RERSULTS: [-7.88412e+26 3.67428e-08 -8.21574e-17 0.00254942
2.66434e+19 -6.76475e+30 -2.80484e+28 ... -4.75018e-17]
On 9 July 2011 13:41, dpath2o<[email protected]> wrote:
Hi Chris,
The readflex documentation is not clear on how to swap byte order. Can you
give a standard example?
Yes, the documentation is not complete on this point.
Basically for the 'f77' and 'swap' toggles, they need
to be the first headers before the one to read any
data as they just change the state of the IO. E.g.,
$data = readflex($fh,
[ { Type=>'swap' },
{ Type='float', NDims=>1, Dims=>[512] }
] );
appears to be the syntax to use or just a line by
itself in a .hdr file.
Cheers,
Chris
On 7 July 2011 21:11, chm<[email protected]> wrote:
On 7/7/2011 2:55 AM, dpath2o wrote:
Chris, et. al.
I'm through the header and now into the data portion of this file. I have
used your suggestions to get through the header and they have worked
really
nicely.
I have successfully read the data into a piddle with the following
command:
my $data = readflex($fh, [ { Type=>'float', NDims=>3,
Dims=>[$Dpplr_n,10,$rng_n] } ] );
Note: the 10th dimension there is because of a quality control values for
each range cell.
However, that method makes getting out the data a little more tricky and
the
following method is more intuitive:
for (my $i=0; $i<$rng_n; $i++) {
my @data = readflex($fh, [
{ Type=>'float', NDims=>1, Dims=>[$Dpplr_n] },
{ Type=>'float', NDims=>1, Dims=>[$Dpplr_n] },
{ Type=>'float', NDims=>1, Dims=>[$Dpplr_n] },
{ Type=>'float', NDims=>2, Dims=>[2,$Dpplr_n] },
{ Type=>'flota', NDims=>2, Dims=>[2,$Dpplr_n] },
{ Type=>'float', NDims=>2, Dims=>[2,$Dpplr_n] },
{ Type=>'float', NDmins=>1, Dims=>[$Dpplr_n] }
]);
}
My problem that I'm stuck on right now is verifying that the data is
actually the data!
If the reading is correct, I would expect the values to
be identical. The general approach I use is to read a single
chunk of data by hand in the pdl2 shell doing one readflex()
at a time and verify the data step-by-step.
Some problems you might be having (the kind I usually
see myself):
(1) perl is 0 based and matlab is 1 based array indexing
so you could confirm that the offsets are not off-by-1
(2) data big/little-endian issues (does the data look
better if you swap bytes or reverse them? try using
unpack on the data chunk using the get_dataref trick
to investigate.
(3) dimension order for matlab and PDL multidimensional
data is different---probably not the issue here with
all the 1-D reads, but it could be.
Hope this helps,
Chris
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