About heading data

Heading data are records of the direction the platform is pointing at a given time expressed as a bearing, in degrees.

Heading variables can be derived directly from some echosounder data files (Simrad Ex60 .raw, .ek60 and .ek6 files, Simrad SM2000 files, and RESON 8000 series snapshot files) or can be derived from .heading.csv files which have been added to the EV file separately. NMEA heading data is also supported for some file formats.

You select which source of heading data is used, either the cruise track or a heading variable (if available), by making a selection on the Attitude page of the Platform Properties dialog box.

Echoview derives heading data from a cruise track as follows:

• If ping time and position fix time are not equal, the bearing is calculated as the direction of travel from the previous position fix to the next position fix.
• If ping time and position fix time are equal, the bearing is calculated as the average direction of travel from the previous position fix to the current position fix and from the current position fix to the next position fix.
• Echoview assumes constant heading before the first GPS fix and after the last GPS fix

Note: In previous versions of Echoview, there was a single source of heading data. Heading data was derived from cruise tracks by comparing consecutive GPS fixes to see in which direction the platform was pointing. From Echoview 3.20 onwards, heading variables are also supported.

Heading data can be used as an input operand with the Motion Range Bitmap operator.

What is affected by heading data?

Heading data affects the transducer position and thus any process that is associated with or uses the transducer position. Transducer position is the geographical location of the transducer in latitude and longitude and is determined by comparing the location of the GPS antenna with the location of the transducer plus the direction in which the platform is moving. See About transducer geometry.

For single beam, dual beam, split beam and multibeam data files, the processes in Echoview that are affected by heading data are listed in the table below.

Note: Heading data also affects the platform heading of Platform referenced scene display.

See also

Exporting heading data
Heading graph
Heading data file format
Creating 3D objects