在 Python 中解释二进制数据

Question

I am using Python 2.7

I am trying to use a large binary file that specifies the latitude/longitude of each pixel of an image.

Using this code: open('input', 'rb').read(50)

The file looks like this: \\x80\\x0c\\x00\\x00\\x00\\x06\\x00\\x00.\\x18\\xca\\xe4.\\x18\\xcc\\xe4.\\x18\\xcf\\xe4.\\x18\\xd1\\xe4.\\x18\\xd3\\xe4.\\x18\\xd5\\xe4.\\x18\\xd7\\xe4.\\x18\\xd9\\xe4/\\x18\\xdb\\xe4/\\x18\\xdd\\xe4/\\x18 ...

The read-me for the file gives the following information for decoding but I am unsure of how to apply them:

The files are in LSBF byte order. Files start with 2 4-byte integer values giving the pixel and line (x,y) size of the file. After the files have succeeding pairs of elements are 2-byte integer values of latitude and longitude multiplied 100 and truncated (eg 75.324 E is "-7532").

Thanks for any help.

Note the reason for doing this ultimately would be to draw/alter an image based on lat/long and not the pixel # in case anyone was wondering.

Answer 1

Generally when working with binary files you'll want to use the pack and unpack ( https://docs.python.org/2/library/struct.html ) functions. That will allow you to control the endianess of the data as well as the data types. In your specific case you'll probably want to read the header info first, something like

with open('input', 'rb') as fp:

    # read the header bytes to get the number of elements

    header_bytes = fp.read(8)

    # convert the bytes to two unsigned integers. 

    x, y = unpack("II", header_bytes)

    # Loop through the file getting the rest of the data
    # read Y lines of X pixels

    ...

The above was not actually run or test, just trying to give you a general sense of an approach.