Re: Reading an odd-format ascii file

Dave,

That appears to get me on-track. Thanks!

gerry

On Tue, Jan 22, 2013 at 3:27 PM, Gerry Creager - NOAA Affiliate <
gerry.creager@noaa.gov> wrote:

> Dave,
>
> Thanks. I'm playing with it now. Will advise.
>
> Regards,
> Gerry
>
>
> On Tue, Jan 22, 2013 at 3:05 PM, Dave Allured - NOAA Affiliate <
> dave.allured@noaa.gov> wrote:
>
>> Gerry,
>>
>> Your excerpt from the manual is a bit unclear. The data values are
>> coded in 5-character groups, hexadecimal, all on one long line of
>> text. They decode into signed integers.
>>
>> To process in NCL, read in a file as all strings, identify the data
>> lines, break into 5-character substrings, then translate the hex
>> substrings to normal integers. You will have to do your own scaling
>> later, because I do not see the relevant information on scaling.
>>
>> Special handling is needed for negative numbers with 5-character
>> hexadecimal format. The stringtoint function treats all such hex
>> strings as positive numbers. See the correction in the demo code
>> below. As usual, "there is more than one way to do this".
>>
>> begin
>> infile = "ceilo.test"
>> data_line = 6 ; 1-based input line number
>> hex_len = 5 ; number of chars in each hex substring
>>
>> lines = asciiread (infile, -1, "string")
>> hex_line = lines(data_line-1)
>>
>> nchars = strlen (hex_line)
>> nvals = nchars / hex_len ; integer division truncates
>> print ("Number of 5-character hex values = " + nvals)
>>
>> hex_strs = str_split_by_length (hex_line, hex_len)
>> ints = stringtoint ("0x" + hex_strs(0:nvals-1))
>> ; add prefix to get hexadecimal translation
>>
>> max_neg = stringtoint ("0x80000")
>> ints = where (ints .lt. max_neg, ints, ints - (max_neg * 2))
>> ; correction for negative numbers
>>
>> print (ints(0:3))
>> print (ints(766:))
>> print ("Min, max = " + min (ints) + ", " + max (ints))
>> end
>>
>> --Dave
>>
>> On Tue, Jan 22, 2013 at 12:55 PM, Gerry Creager - NOAA Affiliate
>> <gerry.creager@noaa.gov> wrote:
>> > I'd posted this some time in the past, but don't recall seeing a
>> solution. I
>> > had to drop this but am now revisiting it for some upcoming field tests.
>> >
>> > I've a file from a Vaisala CL-31 ceilometer, in the "normal" ASCII
>> > representation that I need to read in. I intend to output the thing in a
>> > NetCDF format consistent with what the ARM project has for ceilometer
>> data;
>> > I can handle that once I've got the data read in, I believe... I also
>> want
>> > to be able to plot the backscatter data over time.
>> >
>> > I'm particularly stumped by the 4th line of data. The data format is
>> > described in the manual:
>> >
>> > 4TH LINE (5TH LINE OF MESSAGE NO. 2)
>> >
>> > Example: 00000111112222233333........(5 x 770 bytes)↵
>> >
>> > The two-way attenuated backscatter profile with sensitivity
>> >
>> > normalized units (100000·srad·km)-1 unless otherwise scaled by the
>> >
>> > SCALE parameter. Each sample is coded with a 20-bit HEX ASCII
>> >
>> > character set; msb nibble and bit first, 2's complement. The length of
>> >
>> > this line is equal to 5 times the length of the profile + 2.
>> >
>> >
>> > I'm thinking I should be able to read it in fairly easily to an array,
>> and
>> > operate on the array, then write it back out as NetCDF with the values
>> > already corrected for extinguishment and scaling. However, I've been
>> > unsuccessful to date.
>> >
>> > The attached file is a single time sample.
>> >
>> > Thanks!
>> >
>> > gerry
>> >
>> > --
>> >
>> > Gerry Creager
>> > NSSL/CIMMS
>> > 405.325.6731
>>
>
>
>
> --
> Gerry Creager
> NSSL/CIMMS
> 405.325.6731
>

-- 
Gerry Creager
NSSL/CIMMS
405.325.6731

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Received on Tue Jan 22 14:30:32 2013