Assure that the
setup procedures have been completed, and that the sensor display
shows as the correct horizontal distance behind the boat/operator
(see the SETUP help topic for a discussion of the importance of
proper sensor positioning – this will have a direct bearing
on the accuracy of survey results).
When the sensor
is positioned properly and is returning good data, click on Zero
Mag (or press the Page Up key or press the Alt-Z keys). This
will zero the magnetometer graph and establish a reference gamma
reading. It is not necessary to "Zero Mag" if
using a metal detector -- instead, adjust the metal detector to
the proper gain and offset.
With the boat in
motion and with the sensor tracking directly behind, when a
convenient starting point for the survey is crossed, click on Set
Origin (or press the Page Down key, or press the Alt-O keys). This
will display a notice indicating to the operator to click on a
screen starting point. This will now be the current position of
the boat’s GPS antenna. The objective is to select a screen
position based on the anticipated search area to be covered. If
the starting point is a detected anomaly, it may be convenient to
select a starting point in the center region of the screen.
East-west parallel tracks are recommended for the survey where
The View 2D/3D
Chart button can be used at any time to alternate between viewing
the 2D or 3D chart. The 3D chart is used for graphic
visualization of anomalies, whereas the 2D chart is used for
accurate and dependable navigation.
MagSurvey is not to be used
for primary boat navigation. The
blank screen background does not mean that there is sufficient
depth of water for navigation, or even that there is water at all.
MagSurvey simply provides directional and earth-positional
information – the boat operator must keep a constant watch
for obstructions and depth of water. MagSurvey neither steers the
boat nor operates the throttle, although both would be possible in
a world without litigation excesses. Perception Systems, Inc. is
not responsible for damage to the boat, sensor, property, or any
GPS position is indicated by the four cyan corners on the plot
window, while the sensor position is indicated by the four yellow
corners. The arrow pointer may be moved around in the plot window,
and its location is displayed -- along with data pertinent to the
location. The pointer latitude and longitude values indicate the
center of the map element beneath the pointer.
magnetometer has been zeroed, the origin has been set, and good
data is being received from the magnetometer, GPS, and
differential correction source, the Start Logging and Stop Logging
buttons are used to allow logging of anomalies and map element
positions visited. It is important to Stop Logging whenever the
sensor is not tracking directly behind the boat’s displayed
track-over-ground (TOG). The Home and End keys will also start and
stop logging, respectively. Any time the magnetometer’s
sensor is within a map element, the largest peak positive and peak
negative anomalies are compared to any previously-recorded
positive and negative peaks, and the resultant stored values are
the most positive and most negative values sensed within the map
surveys, since the computed sensor position is determined
from GPS track-over-ground information (TOG), care must be taken
to assure that the boat always has a positive forward motion
whenever logging is enabled. Maintaining speed-over-ground
(SOG) of one knot or greater is recommended (faster if there are
For best results,
it will be necessary to re-zero the magnetometer from time-to-time
to cancel-out unwanted drift due to natural gradation of the
earth’s magnetic field, diurnal changes, sunspot variations,
and small errors due to direction and proximity to the boat.
LANDMARKS AND OTHER POINTS OF INTEREST
operations, points of interest, such as property borders,
permanent buoys, etc., can be recorded on the 2D plot screen by
clicking the Mark Plot button while located at that point of
interest. The background for the point shows as a lighter
shade of gray.
operations, if a known error is logged at a map element due to a
magnetometer glitch, towing problem, or other situation, the data
for that map element may be erased by positioning the pointer over
the map element and double-clicking with the pointing device. A
unique pattern is displayed at that position for the duration of
the survey to show that data has been erased.
data can be
easily saved as often as desired by clicking the Save Survey
button (the Alt-F followed by Alt-S keys may be used to obtain the
same results). A message box will appear to assure that a
save is intended – Click OK to save the plot and all data.
The name of the saved file includes the full date and time of
saving for unmistakable and chronological file identification. The
filename consists of a letter (F for extra coarse scale, E for
coarse scale, R for rough scale, D for default large scale, C for
medium scale, or B for small-scale), followed by a four digit year
number, followed by a two digit month number, followed by a two
digit day number, followed by the letter "T" (for time),
followed by a two digit hour number (military 24-hour time),
followed by a two digit minute number, followed by a two digit
seconds number. The saved survey files are located at
C:\MagSurvey\Surveys, in case you wish to back them up later to
Retrieving a stored survey will wipe out any on-screen plot data –
if there is any data on the screen that should be saved, select
Save Current Plot Survey first.
previously-recorded survey can be quickly loaded by clicking File
selecting Load Previous Plot Survey, and selecting one of the
options below. These menu selections are located in the upper left
corner of the screen (the appropriate Alt-key codes may be used to
obtain the same results). Two operational modes are supported.
MagSurvey must be set to the compatible scale for the file that
you wish to load.
Mode -- The
file will be loaded, and the boat/operator's current and
subsequent positions will be superimposed for analysis, or for
navigation. On-screen displays indicate the distance and bearing
of the boat to any map element beneath the arrow pointer. In
review mode, an option to save the on-screen survey as a bitmap
image becomes active under the File menu at the upper left corner
of the screen.
Mode – The
file will be loaded, and the current and subsequent positions of
the boat/operator and sensor will be superimposed for the purpose
of adding to a previous survey that may be incomplete. As with the
other modes, the distance and bearing of any map element is
indicated on screen when a map element is selected by the
Selecting New Plot Survey will wipe out any current on-screen
survey data – if there is any data on the screen that should
be saved, select Save Current Plot Survey first.
A new plot survey
can be begun at any time by clicking File and New Plot Survey in
the upper left corner of the screen (the Alt-F and Alt-N keys may
be used to obtain the same results). The screen will be cleared
and a new origin must be set.
Donald O. Land
8117A Northboro Ct, West Palm Beach, FL 33406