[ncl-talk] Skip Over Header in Binary File

[Greg Deemer]

Thanks, Dave! I’m up and running again. 

Cheers,
Greg

From:  Dave Allured - NOAA Affiliate <dave.allured at noaa.gov>
Date:  Monday, June 26, 2017 at 5:49 PM
To:  Greg Deemer <greg.deemer at nsidc.org>
Cc:  <ncl-talk at ucar.edu>, Gregory Deemer <gregory.j.deemer at gmail.com>
Subject:  Re: [ncl-talk] Skip Over Header in Binary File

Greg,

Read the entire file as flat binary.  Set the second argument to -1 to indicate unknown dimensions; this will read the whole file.  Set the third argument to "byte" or "ubyte" to match the intended signedness of the data.

    x = cbinread ("file.bin", -1 ,"byte")

Then remove the header bytes using a subscript range expression.  Remember, NCL subscripting is zero-based:

   x2 = x(300:)

I would use dimsizes to confirm that the result has the expected number of bytes.  Then use function onedtond to reshape the x2 array from 1-D to 2-D.

--Dave


On Mon, Jun 26, 2017 at 5:33 PM, Greg Deemer <greg.deemer at nsidc.org> wrote:
Hello, and thank you for addressing my question.

I’m wanting to read some data stored in an unsigned flat binary one-byte integer format. As such, the endianness is thankfully irrelevant. I know the data array will have a shape (/448, 304/), but it is stored after a header that is 300 bytes long. After reading through the binary guidance and hints (https://www.ncl.ucar.edu/Applications/r-binary.shtml), I’ve been unsuccessful in getting started. For some other languages I’ve used, there is a ‘skip bytes’ flag that can be added to read functions to make this process a bit simpler. I thought that was where the “rec_num” came in for fbindirread, fbinrecread, and craybinrecread. I.e. rec_num = 299 would then allow the function to start reading at location 300, byte 301? 

The data file I’m trying to read is attached to this message. If the attachment is blocked, you can download direct from this HTTPS site (but will need a public NASA Earthdata Login Profile setup to do so): https://daacdata.apps.nsidc.org/pub/DATASETS/nsidc0051_gsfc_nasateam_seaice/final-gsfc/north/daily/2006/nt_20060101_f13_v1.1_n.bin

Any help in learning how to skip over some bytes would be great!

Thanks,

Greg Deemer

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman.ucar.edu/pipermail/ncl-talk/attachments/20170627/d3ad2bb9/attachment.html