© Valeport Limited 2003
MIDAS Surveyor Operating Manual
Page 24
0420805d.doc
4.2.9.4
Antenna Offset
The position given by the GPS system is that of the antenna. For survey data to be as accurate as possible, the relative
position of the antenna to the transducer should be known. Ideally, the GPS antenna will be fixed directly above the
transducer, but this is not always practical. In such circumstances, the antenna offset should be entered into the instrument.
Enter the 3D offset as X, Y and Z values:
X
Antenna offset across the boat in metres, with the antenna positioned to Starboard being entered as +ve,
and the antenna to Port being –ve.
Y
Antenna offset along the boat in metres, with the antenna positioned to Forward being entered as +ve, and
the antenna towards the Stern being –ve.
Z
Antenna offset above the transducer in metres, entered as a +ve value.
4.2.9.5
Heading Source
The GPS data string will proved vessel heading information, but this may be unreliable at slow speeds. If the user
decides to use an external heading input such as a Gyrocompass in preference, this must be entered. Use up or down
to toggle between “Heading from GPS” and “Heading from Auxiliary Input”.
4.2.10
SENSOR SETUP
This section of the menu allows the user to setup the Surveyor to receive data from other external inputs, specifically
sound velocity, tide, heave and gyro/auxiliary.
4.2.10.1 Velocity Sensor
Use this function to toggle the measurement of sound velocity from an external device on and off. Arrow keys to toggle,
Enter to confirm. Turning this on opens the appropriate communications port (baud rate set under The RS232 Com
Setup, Section 4.2.4). Data will be updated on the screen at the rate at which it comes in, but will only be logged
according to the interval set under the Logging Setup (Section 4.2.3)
4.2.10.2 Tide Height Setup
4.2.10.2.1 Tide Sensor
The Surveyor will accept a variety of tide data sources. The relevant source should be selected from the available list
using the up, down and enter keys. Available sources are from GPS Height (suitable if an external RTK system is being
used), TIDEGAUGE, which the default format for the Valeport Model 740 tide gauge. There are also 6 generic formats,
which assume that the tide data is at either the beginning or end of a longer data string, and is in either centimetre, metre
or feet format:
cm…TG
TG…cm
m …TG
TG…m
ft…TG
TG…ft
