Hydromagic GNSS heading Plugin

The Hydromagic GNSS heading plugin is a plugin which allows you to get very accurate heading readings. Accurate heading readings can significantly improve your survey or dredging accuracy. Please note that a single GNSS or RTK receiver only outputs a valid heading when your vessel is moving at a certain speed.

An exception is when your RTK receiver is placed exactly above your echo sounder transducer (on the same pole). In this scenario using two GNSS or RTK receivers does not contribute to a higher quality survey because the heading information is not used at all.

Some receivers use two antennas to calculate the heading. In this case you do not need to use this plugin because the heading is calculated internally in the receiver. Use this plugin only when you are using two separate GNSS (GNSS) or RTK receivers!

How does it work?

When you have two GNSS or RTK receivers placed in a line perpendicular or parallel to the vessel’s length, the heading of the vessel can be calculated by using the Vincenty's formula on the geographic coordinates outputted by the GNSS or RTK receivers. When the vessel turns, both the locations of the antennas will change and a new heading is calculated.

GNSS or RTK receiver?

Regular GNSS receivers without a correction signal should work fine. It is correct that they have a rather big error (up to three meters), but since the antennas are so close to each other, the factors that will lead to a position error are almost the same for both, making that the calculated heading is not far off.

However, when using two separate receivers, at some moments one receiver could use different satellites than the other, or one is receiving a SBAS signal while the other is not. When you also have to take tides in account, you should definitely go for an RTK receiver.

Loading the GNSS heading plugin

To load this plugin, open the Preferences window by selecting 'Preferences...' from the 'Options' menu. In the window that appears, select the "Devices" tab. Next, click the 'Add...' button.

A list of available plugins will be displayed. In this list, select the "RTK heading plugin for Hydromagic" plugin and click "OK" to load and display the configuration dialog.

Configuring the GNSS heading plugin

Serial Communications

First, you must configure the serial communications with the GNSS receivers. For each GNSS, select the serial port number and speed. The receivers can be connected via a serial port or Bluetooth serial connection.

As you can see in the configuration dialog, there is a primary and secondary GNSS. The primary GNSS is the one the software is going to use for the vessel's position. The secondary GNSS will be used to calculate the heading only. When you define the GNSS position in the 'Vessel Designer', always use the position of the primary GNSS antenna.

Offset

This field allows you to enter an offset which will be applied to the calculated heading. When the GNSS antennas are lined up in the length of the vessel, you can leave this setting at zero degrees.When the GNSS antennas are positioned side by side, you will notice that there is a difference of 90 degrees between the vessel and the calculated heading. In this case you must enter an offset of +90.0 or -90.0 degrees.

Advanced Settings

Depending on whether you are using an RTK GNSS system or not, select the GNSS quality to expect so heading is calculated when both receivers have the same fix state.
When using RTK receivers, please set this value to 'RTK Fixed' for the highest accuracy.

The smoothing option is optional, when you find the calculated heading to be unstable, you can smooth it out with this function. should not be needed when using RTK receivers, though. If using a smoothing level, it might take somewhat longer to get a heading calculation (up to forty-five seconds).

Unloading the GNSS heading plugin

To unload the GNSS heading plugin, open the preferences window by selecting "Preferences..." from the "Options" menu. In the window that appears, select the "Devices" tab. Next select the "RTK heading plugin for Hydromagic" and click the "Remove..." button.