Using a Second GPS for Heading

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海洋調査機器 > 海洋調査機器 FAQ -よくあるご質問- > HYPACKに関する質問 > Using a Second GPS for Heading

Using a Second GPS for Heading

The otfgyro.dll is a custom device driver that first appeared in Hypack 8.9. The otfgyro.dll, when used in conjunction with the nmea.dll, will calculate heading when using two GPS receivers that have their antennas mounted fore and aft of the vessel. This method is often preferred on dredges and barges.

The nmea.dll is used with one GPS to calculate position, and should be designated the vessel origin. This is very important when creating the boat shape. Add the NMEA-0183 device (nmea.dll) in the Hardware program and be sure that Position is the only box checked (Figure 1). Do not check the heading box. This will be calculated by the otfgyro.dll. Under the setup dialog box, check only the position information coming from the GPS. This is usually a GGA or GLL message. Do not check the VTG, as this is heading information that will be calculated by the otfgyro.dll.

Figure 1: NMEA Device driver setup in Hardware

Now you can load the otfgyro.dll (listed as Coastal Oceanographics OTF-Gyro/Comparison) into the Hardware program. Choose otfgyro.dll from the device list. Hardware will only allow you to check the Heading box. Under the Setup button, be sure to check the message(s) coming in from the GPS (Figure 2). You can also set a distance alarm, which will notify you if the calculated distance between the two GPS antennas exceeds the theoretical distance as defined by the offsets entered in the Hardware program. You MUST enter your offsets in this driver. You should be as accurate as you can with these offsets, as this will be key in determining the correct heading.

Your otfgyro setup is complete once you've connected the receivers to your com ports. Survey will now calculate heading based on position of two GPS antennas. Users can also view the OTF window in Survey (see Figure 3), which gives a visual heading representation, and also displays the distance between the two antennas. The Data Display will display heading, and also give you a distance error between the two antennas.