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dnej
07-10-2003, 08:03 AM
Should a GPS be set on true or magnetic north. Also are there any other settings that need changing.
Helping my brother out .
David

aido
07-10-2003, 08:28 AM
depends on your map reference being used? maybe?
i like to keep mine set on magnetic,
agrees with the compass then, which i like to
keep an eye on.
also when stationary or thereabouts, the gps course info
is usually meaningless, it's bearing to the next waypoint is spot
on though, so i find the compass heading better to reference to
for the initial get go from a spot.
ie, if i'm stopped, and then want to head on course of say 180, i'll
power up and steer 180 on the magnetic compass, when the speed
picks up (yeehaa mode) i then use the gps nav screen for steering.

simple eh, short answer then is magnetic.

aido
07-10-2003, 08:33 AM
the other gps settings to check are your map reference
wgs84, magnetic variation +12e, and maybe the
time difference +10 hrs.

neptune
07-10-2003, 09:22 AM
Once you put in the magnetic variation(differs depending on where you are), it will be magnetic north.

dnej
07-10-2003, 10:21 AM
Thanks,
My brother lives at Cleveland, what variation applies?
The reason this has come about,is due to entering GPS references (beacons) from Beacon to Beacon Book , and actually being not at the beacon proper, when the GPS says he should be.
Any help would be appreciated , as he is new to using same.
David

neptune
07-10-2003, 10:58 AM
If cleveland is near Brisbane then I would say about 11.3 east, rounded down to 11 if that's all your GPS allows.

dnej
07-10-2003, 11:19 AM
Yep, about 40 km south of Brisbane, on the bay.
Many thanks
David

Kerry
07-10-2003, 03:36 PM
Thanks,
My brother lives at Cleveland, what variation applies?
The reason this has come about,is due to entering GPS references (beacons) from Beacon to Beacon Book , and actually being not at the beacon proper, when the GPS says he should be.
Any help would be appreciated , as he is new to using same.

Magnetic variation has nothing to do with GPS references (as in coordinates) and if coordinates as input are not actually being the beacon proper then that could possibly be either the position format or incorrect datum.

Ensure the GPS is configured to the same datum as the input coordinates and also the coordinate position formats are the same as configured in the GPS.

As for True or Magnetic north settings these only basically affect bearings, headings etc. Being User configurations it's not so much of what "should" be used but what the user requires. However True or magnetic north configuration isn't the reason for not finding beacons where they are supposed to be.

Cheers, Kerry.

fishsmith
07-10-2003, 05:42 PM
Magnetic North: Is the direction indicated by the nort seeking pole of a freely suspended magnetic needle infuenced only by the earts magnetic field.

True North: The direction of the north pole from any point on the earths surface.

Grid North: The northerly or zero direction indicated by the grid datum of directional reference.

When ploting a bearing from a compass(magnetic bearing) to a map it must be converted to a grid bearing.
Conversely,grid bearings must be converted to magnetic bearings before they can be used with a compass

To convert a magnetic bearing to a grid bearing add the grid magnetic angle.

To convert a grid bearing to a magnetic bearing subtract the grid magnetic angle.

Note: the grid magnetic angle is found between Grid North and Magnetic North on the North point diagram located on maps/charts.

Cheers Smithy...... ;)

Mudcrab
07-10-2003, 07:20 PM
The present position of the Magnetic North Pole is:

N82.000.000 # #W112.400.000

Kerry
08-10-2003, 05:29 AM
The Magnetic North pole is also a bit of a mover as it can wander around in circles (around 100 km or so) in any one day, while moving northwest around 40km a year.

As for GPS receivers, many manufacturers release software updates as appropriate with corrected magnetic variation tables especially for those who use the auto funtion.

Cheers, Kerry.

dnej
08-10-2003, 05:57 AM
So it may be possible that the GPS has not been correctly configured initially.
Great info guys. That will give him something to think about.
Say when are you rescue chaps going to run a GPS course?
Did the radio course get off the ground?
David

Kerry
08-10-2003, 07:12 AM
David, not so much initially but specifically for this exercise as what might be available in the book might not be the format/datum that might ultimately be used.

Not being relevant to this area I'm not aware of just what the datum and position formats are used in the beacon guide.

There would/should (one would hope so anyway) be some explanation of what datum is used as well as the position format, and really the position formats (Degrees Minutes' Seconds" dDD MM' SS.s" or Degrees Minutes and decimal minutes dDD MM.mmm') should be obvious and totally unambiguous.

If it's a datum issue then the distances off the actual beacons will be basically constant.

If a Position format issue then the distances off will vary.

If it's a combined issue then the distances will also be all over the place.


Cheers, Kerry.

dnej
08-10-2003, 07:54 AM
Kerry ,
The distance from the beacons appears to be constant, and that is why my brother thought something was not right. Great information.
I will get him to check out the Beacon to Beacon Book, for the Datum details. Sure is acomplex issue eh what.
Thanks David

Wesley_Pang
08-10-2003, 08:29 AM
David,

I suggest getting a proper charts of the Bay. Beacon to Beacon is OK, but it only has a few co-ordinates. And not Lat and Long grids. Its more like a UBD.

Department of Transport charts of the Bay is the way to go!!!

Have a good read of the GPS manual and get comfortable with using the GPS. Some have a simulation option.

What is the brand/model??

Wes

dnej
08-10-2003, 09:40 AM
Wes,He tells me its a Navman 500 i.
Does that help

David

Luke
25-10-2003, 05:54 PM
Just to make things interesting the difference between the magnetic and geographical north pole is a varying 180 degrees. As you know with magnets opposites attract and the same repel-therefore south is attracted to north and vice versa. So a north pointing needle on your compass is actually pointing to the earths magnetic south pole but it is also pointing to what we know as the geographical north pole!! Made this way to make it easy for us hoomans.