Eye4Software Hydromagic

  Hydrographic Survey Software

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Configuring an NMEA0183 compatible GPS or RTK receiver

The most important device required for this software to work, is a GPS or RTK receiver.
At this moment, all GPS and RTK receivers with a NMEA0183 compatible data output are supported.

The GPS is used to get position, elevation, course, speed and information on GPS quality and / or precision.
When using a RTK receiver in RTK fixed mode, you should be able to get real time tide information as well.

In order to connect a GPS receiver, you need to have at least one serial port available. If there is no port available,
you can add a serial port by using an USB-to-serial converter or a NMEA0183 data combiner equipped with an USB port.
Most RTK receivers also have the ability to connect them via Bluetooth.

Some modern GPS receivers

Because an USB-to-serial converter can cause minor (some brands major) delays (latency) in communications, we recommend to use a multi port serial adapter instead. Multi port serial adapters are available as PCI cards as well as PC-Cards for use in laptops.

In addition to NMEA0183 data over a serial device, Hydromagic is able to read NMEA0183 data over TCP/IP connections.
This allows you to transfer data over, for instance an Ethernet or WiFi connection. Both TCP and UDP protocols are supported.

When using an USB-to-serial converter, make sure it is connected at the time you are going to configure the sounder.
When using Bluetooth, make sure the device has been paired and connected with your computer.

Video tutorial on how to configure a GNSS receiver connected via a serial port.

Supported NMEA0183 sentences for GPS and RTK receivers

Hydromagic is able to decode the following NMEA0183 sentences used by GPS and RTK receivers:

Sentence Description
$GPGGA Global Positioning System Fix Data, Time and Position
$GPGLL Geographic Position - Latitude and Longitude
$GPGSA GPS DOP and Active Satellites
$GPGSV Satellites in view
$GPRMC Recommended Minimum Navigation Information
$GPVTG Track Made Good and Ground Speed
$PTNL,GGK Trimble RTK positioning data and ellipsoidal height


To add a NMEA0183 compatible device to the configuration, select "Preferences..." from the "Options" menu and select the "Devices" tab:

Add a new device to the list

In the devices tab, click the "Add..." button to load a NMEA0183 plugin.
You can load a maximum of four NMEA0183 plugins at the same time.

Select NMEA plugin from the device list

Next, select the first available NMEA0183 plugin in the "Select Device" dialog that appears after clicking the "Add..." button

Communication Settings

After the plugin has been loaded, a configuration dialog is displayed where you can pass the required information to the plugin.

NMEA0183 Plugin Configuration over serial port    NMEA0183 Plugin Configuration over TCP/IP

Connection Type

The NMEA0183 plugin supports two types of connection types: serial and TCP/IP (networked).
When a device is connected through an USB or serial connection, you have to select the "Serial" option.

In cases where the device is connected using an Ethernet cable or WiFi connection,
you have to select the "TCP/IP" option from the "Connection Type" drop down box.

When switching between the "Serial" and "TCP/IP" connection type, the function of the edit and
selection boxes in the "Connection" section will change as can be seen in the two screen shots above.

Serial communication settings

Serial port

Use this drop down box to select the COMxx number of the serial port the device is connected to.
This can be either a regular serial port, or a virtual serial port, which is used by USB to serial and Bluetooth adapters.

Serial speed

The default serial baud rate for NMEA0183 devices is 4800bps. However, some hardware use other speeds (for instance, an AIS receiver will use 38400).
When configuring a RTK receiver, the serial speed can sometimes deviate from the standard. 9600, 19200 and 38400 bps are mostly used on these devices.

Serial format

You can leave this setting at it's default value. Devices that use NMEA0183 protocol with other settings are very rare.

Network communication settings

Socket type

Use the "Socket Type" drop down box to select the TCP/IP protocol used. Possible values are "TCP" and "UDP".
Please refer to the hardware vendor on which option is supported. Most devices support both protocols.

Host IP

The IP address of the device. This value is required only for TCP connections.
For UDP connections, just provide a valid port number.

Host IP port

Enter the IP (TCP or UDP) port number the device is listening on here.
For most wireless NMEA0183 devices, the port 10110 is used, which is the reserved port for NMEA0183.

Miscellaneous settings


Latency (sometimes called lag) is the time between a measurement has been made
(for instance a position fix, or depth) and when the serial data is received by the application.

If this value is know for a certain device, you can enter it here to get more accurate soundings.

NMEA0183 Talker ID settings

Talker ID

Use this option to filter NMEA0183 sentences by talker ID.

It sometimes happens that both echosounder and GPS devices are transmitting GPS sentences,
in this case you can either select the GPS or echosounder by specifying "GP" or "SD" in this field.

Talker ID for multi constellation receivers

When using a multi constellation GPS or RTK receiver, sometimes sentences are sent multiple times with different talker id's.
For instance the data for GLONASS starts with '$GL', the data for GPS with '$GP', the data for Beidou with '$BD', etcetera.
In these cases the combined data starts with '$GN' which stands for GNSS. To avoid duplicate data to be recorded, set the talker id to 'GN'.

Important note on some multi constellation receivers

Some multi constellation data examples

Good: Only position data with 'GP' talker. No need to set filter.

Good: Only position data with 'GN' talker. No need to set filter.

Bad: Duplicate position data where only talker id differs. Set filter to 'GN'.

NMEA0183 sentence settings

To select which NMEA0183 sentences will be decoded, and which ones will be ignored on this channel,
click the "Select sentences..." button.

The dialog that appears allows you to select which sentences are used.
For most GPS devices, selecting only the "GGA" sentence will suffice.

If you choose to use the heading and speed calculated by the GPS device, you should also select the "VTG" sentence.

Select decoded NMEA0183 sentences

Filtering redundant data (or configuring the GPS output sentences)

Some GPS receivers use different sentences to send for instance the position data to the computer.
To avoid duplicate data, this is something we do not want. The best is to configure the GPS to only output the most important sentences like GGA and VTG.

When it is not possible to change the output of the GPS receiver, use the sentence settings to filter out unwanted duplicates.
Find some samples of good and bad NMEA0183 outputs below:

Good: No duplicate data here. No need to set filter, recommended NMEA output settings for GPS receivers.

Bad: RMC already includes speed and heading, so no need for VTG here.

Really bad: The same position is transferred using 4 sentences. Use GGA or GGK only.

NMEA0183 output rates

The output rate is the number of times a particular NMEA sentence is calculated and broadcasted by the GPS or RTK receiver.
By default, for most receivers, the output rate is 1Hz which equals one time per second.

Although Hydromagic works perfectly with an update rate of 1Hz, it is recommended to set it a little higher to improve accuracy.
When for instance the echo sounder has an output rate of 10Hz, the Hydromagic software will calculate the positions for these soundings.

It is doing this by taking the position before and after the echo sounder ping. The more positions there are, the higher the accuracy.
This is especially true when surveying at high speeds, or when there are sudden course or speed differences in your track.

We recommend you to set the GPS at the same output rate as the echo sounder, or at least at the closest as possible value. How to set this value differs per GPS or RTK receiver. Please contact your dealer or refer to the manual for more information.

Modifying NMEA serial output settings on a RTK receiver

Testing the GPS device

When everything has been configured correctly, and the GPS has been switched on and has a valid fix,
the position fields in the "Navigation View" should have green values.

Check incoming position data in data view

Communications monitor

You can always check whether data is received correctly, by running the built-in communications monitor.
Not even can it used to check if data is coming in, but you can also see which NMEA0183 sentences are received.

When data is garbled and you are expecting NMEA0183 data, you have to change the serial baud rate until the data is readable.

To start this monitor, select the "Preferences..." option from the "Tools", and select the 'Devices' tab.
Right click on the device you want to monitor the incoming data from, and select the 'Monitor Device...' option from the pop up menu.

Start the communications monitor to see incoming NMEA data

When the monitor is running you should see NMEA0183 data coming in. You can pause the data at anytime.
For technical support purposes, you can click the 'Copy to Clipboard...' button to copy and paste the incoming data into an email.

Use the communications monitor to check incoming data