Using Hydromagic Survey with a total station

In some cases you might want to use a total station instead of a GPS or RTK receiver. For instance, when creating a sounding below a bridge, or in a mine, you won’t have GPS reception and using a total station would be the only alternative. This tutorial has been written after questions from OceanScience's Z-Boat users utilizing the Hydromagic software to record and process their soundings.

Image courtesy of SurvBase LLC

Total station plugins

Since Hydromagic version 6.0 it is possible to add total station functionality by the use of plugins. At the moment two total station plugins are shipped with Hydromagic. Total stations capable of outputting either the Trimble 'Geodimeter' format or pseudo GGA format are supported. In case you are using a total station which isn’t supported, please contact our support desk.

Depth vs Elevations

When mapping ponds, basins, frac pits or other water surfaces you can choose to map the water level relative to a fixed reference or the absolute depth. In cases when the bottom is measured against a fixed reference, the orthometric height from the total station is used. When mapping depths only, the height value coming from the total station can be ignored.

In short, when a sounding is done to perform volume calculations you only have to record depths.For construction work or tidal areas, most of the times the elevation of the bottom is measured.

Connecting the total station

In order to retrieve the easting and northing (and possibly elevation) coordinates from the total station, it has to be connected directly to the computer using either a serial cable or wireless Bluetooth connection.

In case of a Bluetooth connection, select one of the virtual serial COM ports created by the Bluetooth driver software. Make sure to configure the total station to output coordinates continuously. An output interval of one position per second should suffice.

Loading the total station plugin

When the total station has been connected to the computer, the next thing to do is to load the plugin to get the serial data from the total station decoded and displayed in the Hydromagic Survey application. To do so, select the "Preferences..." from the "Options" menu. Select the "Devices" tab in the dialog box that appears.

To add the plugin for the total station, click the "Add..." button. A list of available plugins will be displayed. Depending on the output format of your total station, select either the "Geodimeter Total Station Plugin" if your (Trimble) total station outputs the Geodimeter format, or the "Trimble Total Station Plugin" for pseudo NMEA (most commonly used).

Click "OK" to confirm your selection and select the correct serial port, serial speed and data format in the configuration dialog that appears.

When done, click the "OK" button twice to store your settings and close the "Preferences" screen.
When all parameter has been set correctly, the position in Easting and Northing should be displayed in green in the "Navigation Data" window.

You can add plugins in the "Devices" tab of the Preferences window.

Surveying in "depth mode"

When surveying in depth mode you should be ready to start your survey as soon as you have setup your echo sounder as well. Please make sure to configure the static draft, which is the height offset between the bottom of the echo sounder transducer and the water surface.

To set this offset, open the "Preferences" screen by selecting "Preferences..." from the "Options" menu. Next click the "Calibration" tab, and enter the absolute offset in the "Transducer Offset" field.

The Transducer offset can be entered in the "Calibration" tab.

Surveying in "elevation mode"

When surveying in elevation mode the elevation of the bottom is measured. Because the level of the water often varies this is taken into account by measuring the water level. This is done by measuring the height of the RTK antenna or total station prism. The offset between the waterline and antenna / prism is subtracted from this value to get the tide level.

When using a RTK receiver the antenna height is measured relative to the ellipsoid (for instance WGS84) and a geoid model is used to calculate the orthometric height. To get the height of the water level (tide), the orthometric height is corrected with the antenna height above the water surface.

When using a total station, ellipsoidal height isn’t used. Instead, the total station outputs orthometric height directly. Because of this, you have to configure the software a little different then when using a RTK receiver.

Configuration for elevation mode

First you have to make sure that the offset between the bottom of the transducer and the water surface is configured. The "Surveying in depth mode" paragraph explains how to do this. Next we have to tell the software that the height coming from the positioning device is orthometric height rather than ellipsoidal height. This can be set in the RTK settings tab.

To open the RTK settings, select "Preferences..." from the "Options" menu and select the "RTK" tab. First check the "Use Real Time Kinematic (RTK) for real time tide calculation" option first. In the height field of the "Antenna height and geoid model" section, you enter the distance between the prism and the water surface.

Finally we have to tell the software that the measured height is orthometric height by checking the option "Treat ellipsoidal height as orthometric height". Because the orthometric height is known, we do not have to select a geoid model. If a geoid model is already selected, it will be ignored. Click "OK" to store the settings and you are ready to start your sounding.

Select the "Treat ellipsoidal height as orthometric height" option.