I have a GPS, which I initially only got as an emergency aid to navigation, in that if I'm really, really stuck, I can fish it out of my bag and it will give me a grid ref.
However, I'd now like to do a bit more with it, so I've been reading up about waypoints and the 'Goto' function. I've got a bit confused about using it in conjunction with a compass though...
...as I understand it, the GPS will give me a compass bearing from my present location to my chosen waypoint. Fine so far, but then the book starts burbling about the magnetic declination, how it is set up in the GPS, and how that affects the compass reading...HELP!
My GPS is set to magnetic in the 'North Ref' page. Does this mean I use my compass as normal, i.e. 'mag to grid, rid', etc, or do I now have to get used to ignoring magnetic variation when using my compass alongside GPS?
The gps should automatically calculate the required magnetic declination depending on where you are in the world. As long as you have set it up correctly for your location EG. correct capital city for location & appropriate grid ref system.
But as far as a bearing goes this depends on the model of gps, if you have a barometric altimeter & a compass built into the gps (which you calibrate after every fresh set of batteries) then the gps will automatically point north.
If the gps does not have this function the the gps's direction will not be accurate until you start moving, as it know where it is but does not know where North is. As soon as you start to move, the gps senses north & will point into the correct direction.
Regarding what the Echidna said, a gps without a built in compass will indeed need to be moving in order to accurately display the direction of your bearing on it's 'compass page' display - if you were trying to actually use that direction of travel arrow to walk accurately to your destination.
However, such a gps will still give an accurate bearing from your position to your destination even when stationary - it knows the co-ordinates of both so it can calculate the bearing between them, i.e. it can display that the bearing is e.g. 274 degrees, but it can't show you what direction that is. This doesn't matter if you plan to dial the bearing in on your 'proper' compass to follow it...
And if you've set the gps to magnetic for its north ref, then the bearing it's showing will already have made the adjustment for magnetic variation - so just set your compass to the displayed number and follow that bearing without any further adjustment.
I was thinking along the lines of just using the GPS to give me an accurate bearing back to my start point, but using the compass for walking along that bearing. I followed the bit about the GPS needing to be moving to show the direction, and also the fact that that particular function drains the GPS battery!
So, I don't need to make any further adjustments. Cheers Matt, (also Kinley and our spiny anteater friend!) I understand now. GPS has already made the adjustment required, so I just follow the bearing that it says.
I suppose you just walk in the general direction, taking into account the terrain features (bog, most likely) and keep on checking and adjusting the bearing as you go, until you arrive back at the start.
That's for tomorrow night, I think, if it looks like being clear and moonlit. It's off to the moors in the dark, up tarp, and off for a wander with GPS/compass, then back to tarp for cocoa and bed!
I think it does (it's just yer basic Garmin etrex model) - but I haven't read that far into my 'GPS for idiots' book yet.
Your Garmin does have 'trackback' so it remembers where you have been.
Is that another feature where you have to be actually moving for it to work?
Yes and no, sometimes it's obvious looking at the track where you are, walking a few steps will let the unit know which way you are facing.
I bought a Garmin 60Csx plus Topo maps so I have paperless mapping with an electronic compass, I can follow a path through the middle of a field in the middle of nowhere in the pitch dark
How does it work? Do you just go to the 'tracks' thingy, enable it, and it does all the tracking automatically? And how do you follow the path backwards - literally just arse about face, and follow the track as it appears on the screen? or are there more buttons to press? and does it 'eat up' the breadcrumbs, so to speak? Is the distance you travelled before you started backtracking recorded?
Mick if you need to trackback to the start point you have to first mark your start point.
1. arrive at start point say by car,get gps out switch it on,let it home in on satalites then goto menu page(mark/track/route/setups)click first one(mark) that then will know where you started your walk from and know where to guide you back too...
2. leave the gps on and put in top of your sack and it will then track you all the way along your walk.
3.when you get to the point where you want to turn around,mark again where you are and then save track.this then should give you the option to save/delete/trackback,goto trackback and just follow the point of direction arrow or the little stick man on the dotted black line,.
4. think thats right and as simple as i can put it for you.you should have got a quik start guide with your gps,try reading and useing that around your streets and get used to it there first before trying on the hill as its a little more pressured when you are relying on it..
I found the best way to learn was to keep playing with it (in the car/kids to school/dog for walk/walk round block etc etc)...and then on the hill......
Its like any new technology mind boggling at first until you play with it more..
Also if using the trackback option remember if you have used it, to clear it each time before you head off, it's memory is large but you don't want to be in a situation where you need to tracback but have run out of recording points..... ahhhhhh Also it is possible to confuse yourself & start tracbacking from a previous outing.....
Well, I won't be tarping it tonite for a number of reasons (too damn tired after mi nites being one of them!) but I have been reading the manual and playing about with my GPS today.
Got a bit confused on the Track thingy, when I was trying to follow it backwards, It took a while for it to sink in that the arrow on the compass face was continually pointing at the destination (my start point) rather than where I should actually be going.
Hang on, if I had gone to the 'map' page, would I have seen the little stick guy re-tracing his steps?
Mick, I'm surprised by what you just said about the arrow pointing at your destination rather than guiding you along the line of the track. Sorry if this comes across as at all condescending, I don't intend to, but are you sure you were following the track back to it's start point as opposed to using 'Goto' on a waypoint taken at the start?
I know Diddy said to mark a waypoint at the start of your walk and at your furthest point before you 'trackback', but my experience (based on a Garmin Geko 201, and a Garmin GPS12 before that) is that you don't actually have to mark any waypoints in order to work with a track - the track, or breadcrumb trail if you like, works independently of marked waypoints.
trackpoints and waypoints require a bit of lateral thinking.
the book tells you that a route is where you are going and a track is where you've been. a good concept to get around but it isn't true. BOTH can tell you where you're going but only a tracklog can tell you where you've been.
digital mapping packages have a different slant on these e.g. memory map distinguishes between a route (waypoints) and a track (trackpoints) whilst tracklogs doesn't.
you need to get your head around these two things.
ok then.
a trackpoint is a piece of data that contains position and a number (so that the machine knows which one follows which).
a waypoint is a piece of data that contains position i.e. EXACTLY the same as a trackpoint EXCEPT a waypoint also allows the addition of text to the data i.e. giving it a name.
you may also interactively create a waypoint when you are out e.g. ah! here's the tent/car/where the caravan used to be before the storm.
therefore, because the waypoint can contain text and other info, it is a larger piece of data than a trackpoint. hence the reason why you many more trackpoints in a gps than waypoints.
you can only enter waypoints directly into the GPS manually i.e. by hand.
you can save tracks and you can save routes into a gps electronically.
the gps always generates a "breadcrumb" trail of where you've been and saves it in the tracklog. you can use this information to download to the pooter where you've been. you can use the trackback feature (from the tracks menu) to retrace your steps - invaluable if you get lost or you don't like the conditions.
you can create a waypoint at any time e.g. here's the tent and then use the gps to navigate back to the tent - but here is a VERY important point. you can find the tent by using the trackback feature and you trackback to the tent waypoint the way you came OR you can GOTO the tent waypoint. however, GOTO anywhere will direct you there in a straight line and a straight line may involve a nice river or cliff in the way.
Nice summary there from Parky In particular the last (crucial) bit about the difference between Trackback and Goto!!
Just one minor quibble....
"you can only enter waypoints directly into the GPS manually i.e. by hand."
I don't think this is true - I can certainly upload Routes, tracks AND Waypoints into my Geko 201 from the PC. It might depend on the PC mapping software you're using? I use Quo for the UK and Garmin Mapsource (without maps!) for preparing foreign trip data, both allow the creation and upload of Waypoints.
IMPORTANT re the gps tracklog. the number of trackpoints in the machine is the TOTAL available. if you have saved a track, those number of points reduce the number now available. you will have a choice as to how the gps will treat these when the number of trackpoints gets full. you can set either for the trackpoint recording to stop OR to keep recording but overwrite the existing tracklog starting at the beginning.
you can also choose the frequency with which the gps will record a trackpoint.
because the tracklog memory fills up ALWAYS delete the contents of it when you start a walk.
if you venture into digital mapping i would recommend that you save your planned trip as a track and not a route. you may only have 250 waypoints for a trip but maybe 10,000 trackpoints for one. use waypoints to mark important spots e.g. camp/water/pub/bus stop/pay attention this bit is tricky/nice view etc.
if doing a long distance path in sections, you can plot the whole path and load it as a track, turn up anywhere on it and tell the gps to trackback to the end.
i would be wary of using the gps compass reading to plug into your compass. it depends how far away the next "point" is. with 5m accuracy the gps is telling you that it thinks you are somewhere in a circle of 5m radius so you could actually be 10m away from where you actually are. this would introduce errors. no problem in daylight but may be when dark/bad visibility.
confusing isn't it!
and a final point. although they are not supposed to do this, experience dictates otherwise. if you have a zig-zag path, the gps MAY point to the next NEAREST point rather than the NEXT point - that nearest point could be at the bottom of a cliff. just to be awkward the little darling machine won't always do this but i would suggest that you assume it always does - better safe etc. you can try it out in the park.
thanks matt.
correction: you can only enter waypoints directly into the GPS manually i.e. by hand, you cannot enter a trackpoint manually.
Re using the gps bearing to transfer to your compass - is the kind of inaccuracy you're describing really going to be any worse than what you's get anyway because of the (lack of) precision when working traditionally with a compass on the (paper) map? On a 1:50k map 1mm is 50m on the ground - can any of us really place our compass that accurately (0.2mm for 10m) and hold it there while we line everything up, rotate the dial and get our bearing from the map, especially if hand-holding the map without a firm suface in a hoolie - just the conditions when the speed of the gps is attractive.*
* with due regard to not totally relying on it, keeping brain engaged and common sense on, etc...
forgive me matt. i have always assumed that those who eschew the gps as a work of multiple demons and sprites and always insist that you should only ever, ever use a map and compass indeed had that level of manual accuracy; or at least implied they had to support their assertation that a gps should not be used in any circumstance.
but more seriously, i mentioned it because it does depend how far away the point is e.g. if you are 10m out at 100m then you have an error approaching 6 degrees which diminsihes to around 0.6 degree at 1km whcih doesn't really matter. (2 degrees at 250m)
with a hand held bearing on a map you allow for the inaccuracy in your mind as experience has taught you to.
No problem Parky, I didn't see your remarks as aimed at me
Again though, just thinking aloud really, if you had say such a 6 degree error but were only walking a 100m leg, how likely is it that visibility would be so bad that you wouldn't see your target by the time you've covered the distance (I suppose that assumes that you're aiming for some recognisable feature.... but usually I would be)
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In particular the last (crucial) bit about the difference between Trackback and Goto!!
