session iii gps depth-finder units. f gps positions are not error free –user and/or satellite...
TRANSCRIPT
Session IIIGPS DEPTH-FINDERUNITS
GPS positions are not error freeGPS positions are not error free
–User and/or Satellite clock bias.–Satellite signal can be blocked.–Atmospheric interference is possible.–Poor satellite geometry is possible.
You can monitor these errors with your GPS receiver.
Signal Quality and Accuracy
The height of the bars in display shows signal strength from each satellite
The “clock face”shows the positions of satellites currently in view to your GPS.
Estimated Position Error“EPE”
Many GPS units display EPE instead of HDOP
– It’s an expression of the diameter of a circle in which your position target exists
– EPE is expressed in feet or meters – user choice
Always validate satellite reception &
accuracy before using your GPS set
for navigation.
GPS Setup ParametersGPS Setup Parameters– True or Magnetic DirectionTrue or Magnetic Direction
– Nautical/Statue MilesNautical/Statue Miles
– Clock –Clock –24hrs24hrs
– Speed in KnotsSpeed in Knots
– Variation – Variation – 013013°West°West
– Horizontal Datum – Horizontal Datum – WGS84WGS84
– Lat & Lon – Lat & Lon – Degrees/Minutes/SecondsDegrees/Minutes/Seconds
Course and BearingsCourse and Bearings
Select a heading format:
–TRUE
–MAGNETIC
GPS reports movement over GPS reports movement over ground - often different than the ground - often different than the vessels heading.vessels heading.
GPS errors affect accuracy.GPS errors affect accuracy.
Always steer off your compass, Always steer off your compass, not the GPS.not the GPS.
GPS is not a CompassGPS is not a Compass
When you are using your GPS on a boat, set the Distance Unit of Measure to Nautical Miles.
Distance
Select a time format:
12 or 24 hour clock format
–UTC or Local time
Time FormatTime Format
When you are using GPS on a boat, set the speed unit of measure to KNOTS
– Nautical Miles Per Hour.
SpeedSpeed
Some GPS receivers are Automatic, some have to be done manually.
Variation is found on the inside of the compass rose.
VariationVariation
WGS84WGS84
Horizontal Datum
WGS-84 is the US standard, NAD-27 is common.
LAT. & LON.LAT. & LON.
Set GPS Unit to
Degrees-Minutes-Seconds 074 – 23 - 39.0
Most units are set
Degrees-Minutes- Tenths of Minute 074 – 23 .650
CONVERSIONS
Decimal portion of Minutes to Seconds
.650 X 60 = 39.0
Seconds to Decimal portion of Minutes
39.0 ÷ 60 = .650
DEPTH-FINDERDEPTH-FINDER
Set your depth sounder to correspond to the vertical datum referenced on the nautical chart that you are using.
Depth MeasurementDepth Measurement
Depth-Finder should be set for chart datumi.e. Feet, Meters or Fathoms
Soundings in Fathoms
REMEMBERREMEMBER
Your depth-finder shows Your depth-finder shows the depth of the depth of
water below you now, not water below you now, not where your going!!!where your going!!!
•It is very important to know where the transducer is mounted
•You need to know the distance from your waterline to the transducer
•You also need to know the distance from the transducer to the lowest point of your boat.
TRANSDUCERTRANSDUCER
END OFSession III