Angular positions in Simrad files are stored in units of electrical phase steps. These are interpreted as follows for each of the supported series of echosounder.
A pair of angles is stored as a 16-bit word in the data file. The most significant byte is the along ship (minor axis) angle. The least significant byte is the athwartship (major axis) angle.
The first bit of each byte stores a sign with 0 positive and 1 negative. The last 7 bits of each byte store a magnitude. This is an integer value, in the range -127 to +127 with units of 'phase steps'.
There are 64 phase steps to 180 electrical degrees, so e (angle in electrical degrees) is calculated as:
e = i * 180 / 64
where:
e is the angle (electrical degrees)
i is the signed integer from the data file ('phase steps')
The mechanical angle is then calculated as:
m = e / sensitivity - offset
where:
m is the mechanical angle (degrees)
e is the angle (electrical degrees)
sensitivity is the value entered on the Calibration page of the Variable Properties dialog box.
offset is the value entered on the Calibration page of the Variable Properties dialog box.
A pair of angles is stored as a 16-bit word in the data file. The most significant byte is the along ship (minor axis) angle. The least significant byte is the athwartship (major axis) angle.
Each byte is interpreted as a signed 2's compliment integer. This is an integer value, in the range -128 to +128 with units of 'phase steps'.
There are 128 phase steps for 180 degrees, so e (angle in electrical degrees) is calculated as:
e = i * 180 / 128
where:
e is the angle (electrical degrees)
i is the signed integer from the data file ('phase steps')
The mechanical angle is then calculated as:
m = e / sensitivity - offset
where:
m is the mechanical angle (degrees)
e is the angle (electrical degrees)
sensitivity is the value read from the data file (visible on the File page of the Information dialog box)
offset is the value entered on the Calibration page of the Variable Properties dialog box.
Simrad data files
Raw variables derived from Simrad data files
EK500 configuration
EK60 configuration