Matlab Training Session 10:
Loading Binary Data
Course Website:
Course Outline
Term 1
1. Introduction to Matlab and its Interface 2. Fundamentals (Operators)
3. Fundamentals (Flow) 4. Importing Data
5. Functions and M-Files 6. Plotting (2D and 3D) 7. Plotting (2D and 3D)
8. Statistical Tools in Matlab
Term 2
9. Term 1 review
Week 5 Lecture Outline
loading Binary Data
A. Week 5 Review – Importing Text Data
B. Binary Encoding
A.
Week 5 Review:
Importing Text Data
• Basic issue:
– How do we get data from other sources into Matlab so that we can play with it?
• Other Issues:
– Where do we get the data?
• Lots of options to load files
– load for basics
– fscanf for complex
– textread for any text
load
• Command opens and imports data from a
standard ASCII file into a matlab variable
• Usage: var_name
= load(‘filename’)• Restrictions
load
• Works for simple and unstructured code • Powerful and easy to use but limited
• Will likely force you to manually handle simplifying data which is prone to error
File Handling
• f* functions are associated with file opening, reading, manipulating, writing, …
• Basic Functions of Interest for opening and reading generic files in matlab
– fopen – fclose
– fseek/ftell/frewind – fscanf
fopen
• Opens a file object in matlab that points to
the file of interest
• fid = fopen(‘filepath’)
• fid is an integer that represents the file
fclose
• When you are done with a file, it is a good idea to close it especially if you are opening many files
What is a File?
• A specific organization of data • In matlab it is identified with a fid
• Location is specified with a pointer that can be moved around
file_name
fid
Moving the Pointer
• We already know how to assign a fid (fopen) • To find where the file is pointing:
– x = ftell(fid)
• To point somewhere else
– fseek(fid,offset,origin)
• Move pointer in file fid by offset relative to origin
– Origin can be beginning, current, end of file
• To point to the beginning
Getting Data
• Why move the pointer around?
– Get somewhere in the file from where you want data
• fscanf(fid
,format,size)
• Format
– You have to tell matlab the type of data it should be expecting in the text file so that it can convert it
• ‘%d’, ‘%f’, ‘%c’ • Size
– You can specify how to organize the imported data
• [m,n] – import the data as m by n, n can be infinite
Getting Data
• fgetl returns the next line of the file as a character array
• You may need to convert these to numbers
>> fid1 = fopen(‘test1.txt’);
>> a_str = fgetl(fid1)
a_str = 1 2
>> a_num = str2num(a_str)
B. Binary Encoding
• All data files are binary encoded
• ASCII text format is generally the easiest
because it is relatively simple, easy to visualize in a text editor, and is a common output format
BUT
• ASCII text is not the fastest or the most efficient way of encoding data
B. Binary Encoding
• Binary data consists of sequences of 0’s and 1’s
• 10101010101010101000010111110111101011
• Depending on the encoding used, individual
meaningful values will occur every 4, 8, 16, 32 or 64 bits
B. Binary Encoding
• Binary data consists of sequences of 0’s and 1’s
• 1010 1010 1010 1010 1000 0101 1111
• Depending on the encoding used, individual
B. Binary Encoding
• Binary data consists of sequences of 0’s and 1’s
• 10101010 10101010 10000101 11110111
• Depending on the encoding used, individual
B. Binary Encoding
• Binary data consists of sequences of 0’s and 1’s
• 1010101010101010 1000010111110111
• Depending on the encoding used, individual
B. Binary Encoding
• Each group of bits can represent a value,
character, delimiter, command, instruction ect.
• Generally binary data is divided into 8 bit (1 byte) segments
• 00000000 = zero • 11111111 = 255
ASCII ENCODING
• ASCII: American Standard Code for Information Interchange (1968).
• ASCII every character is coded by only seven bits of information. The eighth bit is ignored (it can be a zero or one).
• ASCII consists of 127 characters which include uppercase, lowercase, spaces and formatting
characters
ASCII vs Simple Binary
Encoding
• ASCII requires 1 byte to be used for every character
Data Table: 105 124 27 101 102 111
• In ascii 1 byte is used for every character, space and carriage return = 23 bytes
Binary Precision
• The number of bits used to represent a value determines how large or small that value can be
•8 bits 0 to 256
•16 bits 0 to 65536
•32 bits 0 to 4.2950e+009
'schar' Signed character; 8 bits 'uchar' Unsigned character; 8 bits 'int8' Integer; 8 bits
'int16' Integer; 16 bits 'int32' Integer; 32 bits 'int64' Integer; 64 bits
'uint8' Unsigned integer; 8 bits 'uint16' Unsigned integer; 16 bits
* The first bit denotes the sign if the integer or character is signed.
C. Binary Formats:
Readable Binary Data Formats
Floating Point Representation
Used for numbers that require decimal representation (real numbers)
•Established by IEEE (Institute of Electrical and Electronics Engineers )
• Encoded in 32 (single precision) or 64 bits (double precision)
• Single precision(short): 32 bits 1 bit for the sign, 8 bits for the exponent, and 23 bits for the mantissa.
Readable Binary Data Formats
Floating Point Representation
• By default matlab stores all values with double precision
• The functions realmax and realmin return max and min value representations
Specifying Machine Formats
• The computer system used to record or save the binary data in unique addressing orders
• In order to load binary data from a particular system, Matlab needs to know the machine format
•You can use the fopen function to determine the machine format
Binary File Machine Formats
'ieee-be' or 'b‘: IEEE floating point with big-endian byte ordering 'ieee-le' or 'l' : IEEE floating point with little-endian byte ordering 'ieee-be.l64' or 's‘: IEEE floating point with big-endian byte ordering and 64-bit long data type
'ieee-le.l64' or 'a‘: IEEE floating point with little-endian byte ordering and 64-bit long data type
'native' or 'n' : Numeric format of the machine on which MATLAB is running (the default)
Reading Binary Data
• The function fread() performs all binary data reading in matlab
Syntax
A = fread(fid)
A = fread(fid, count)
A = fread(fid, count, precision)
A = fread(fid, count, precision, skip)
Reading Binary Data
Input Arguments:
Count: x: read x elements Inf: read to end of file
[m,n]: read enough to fill a m by n matrix
Precision: Specify input data format eg. Int8, int16, short, long… see previous slides
Skip: Skip specified number of bits between
segments specified by the Precision argument
Exercise
Load and plot position data saved in: week10data.rob
• This file contains binary position data saved in 32 bit floating point format precision
1. Use the fopen function to determine the machine format hint: [fname, mode, mformat] = fopen(fid)
2. Load the data using the fread function 3. Plot the position
Exercise Solution
fid = foopoeono(o'wdeoeo1�0edataat.rrobr'w''wr'w羂 %oopoeono fileo foor reoatdinnoe
%oDeoaeorminnoeo fileo foormata
[fonoatmeo' modeo' mfoormata] = foopoeono(ofid羂
%oFormata ins ineoeoeo-leo
%oReoatd brinnoatry dataat
Getting Help
Help and Documentation Digital
1. Accessible Help from the Matlab Start Menu
2. Updated online help from the Matlab Mathworks website:
http://www.mathworks.com/access/helpdesk/help/techdoc/matlab.html
3. Matlab command prompt function lookup 4. Built in Demo’s
5. Websites
Hard Copy
3. Books, Guides, Reference
