Eye4Software Hydromagic

  Hydrographic Survey Software

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Hydromagic GPS heading Plugin

The Hydromagic GPS 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 GPS or RTK receiver only outputs a valid heading when your vessel is moving at a certain speed.

An exception would be when your RTK receiver is placed exactly above your echosounder transducer (on the same pole). In this scenario using two GPS or RTK receivers does not contribute to a higher quality survey since 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 since the heading is calculated in the receiver internally. Use this plugin only when you are using two separate GPS (GNSS) or RTK receivers!

How does it work?

When you have two GPS 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 GPS or RTK receivers. When the vessel turns, both the locations of the antenna's will change and a new heading is calculated.

GPS or RTK receiver?

Regular GPS receivers without correction signal should do 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, in the scenario when using two separate receivers, at some moments one receiver could user other satellites then 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 definitly go for a RTK receiver.

Loading the GPS 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.

the devices tab in the preferences dialog

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.

select the Hydromagic GPS heading plugin

Configuring the GPS heading plugin

Serial Communications

First you must to configure the serial communications with the GPS receivers. For each GPS, 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 config dialog, there is a primary and secondary GPS. The primary GPS is the one the software is going to use for the vessel's position. The secondary GPS will be used to calculate the heading only. When you define the GPS position in the 'Vessel Designer', always use the position of the primary GPS antenna.


This field allows you to enter an offset which will be applied to the calculated heading. When the GPS antennas are lined up in the length of the vessel, you can leave this settings on zero degrees. When the GPS antennas are positioned next to each other, 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 the GPS system you are using (RTK or not), select the GPS 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 found the calculated heading to unstable, you can smooth it out with this function. Should not be needed when using RTK receivers though. When using a smoothing level, it might take somewhat longer to get a heading calculation (up to forty-five seconds).

the GPS heading plugin configuration dialog

Unloading the GPS heading plugin

To unload the GPS 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.

Unload the Hydromagic GPS heading plugin