I am new to the GPS thing and just got a GPSmap 62st. I am a bit confused when not using a printed map and just the Garmin map while out hiking which map datum is the Garmin map based on? WG84, NAD 27, etc so I can set my GPS to that one? Or does it matter? I see in the manual about waypoint averaging for more accuracy but it doesn't go into any details on how. Hiking the Alaska back country I do need as much accuracy as I can get, not really wanting to end up as dinner for our bears! Thomas:confused:
When working a gps by itself, it will give you an accurate position, within the instrument's capabilities and satellite reception/geometry etc. It is when working with others and/or paper maps that you need all to be on the same page, meaning datum.
Actually, the differences between WGS84 and NAD27 are not that huge, depending on where you are, but it certainly can complicate things.
If calling for rescue, better use WGS84 (or NAD83, which is virtually the same).
Now position notation is even more critical as the errors introduced by incorrect use of lat/long notations can have a dramatic effect on position.
Decimal degrees, degrees and decimal minutes, degrees-minutes-seconds, are all quite different. You need to make sure all parties use the same notation.
Take your gps on small scale hikes, in a well known area. Let it do the navigation for you. Learn its strengths and weaknesses and remember, it is only good if you pack enough batteries. Use map and compass as backup.
I am a bit confused when not using a printed map and just the Garmin map while out hiking which map datum is the Garmin map based on?
The datum is selected in your 62S (WGS84 is the default). You have a choice of many. You can also (independently) select your grid (lat/lon, UTM etc). If you configure the unit the same way as your paper map you should be close.
I see in the manual about waypoint averaging for more accuracy but it doesn't go into any details on how.
Waypoint averaging works by taking multiple samples of your position and averaging them to (theoretically) remove errors. For this to work you have to remain stationary for the period of the averaging. You might want to Google this but I think a period of 5 mins (300 secs) improves accuracy significantly.
When working a gps by itself, it will give you an accurate position, within the instrument's capabilities and satellite reception/geometry etc. It is when working with others and/or paper maps that you need all to be on the same page, meaning datum.
Actually, the differences between WGS84 and NAD27 are not that huge, depending on where you are, but it certainly can complicate things.
If calling for rescue, better use WGS84 (or NAD83, which is virtually the same).
Now position notation is even more critical as the errors introduced by incorrect use of lat/long notations can have a dramatic effect on position.
Decimal degrees, degrees and decimal minutes, degrees-minutes-seconds, are all quite different. You need to make sure all parties use the same notation.
Take your gps on small scale hikes, in a well known area. Let it do the navigation for you. Learn its strengths and weaknesses and remember, it is only good if you pack enough batteries. Use map and compass as backup.
I've wondered similar things regarding datum. For example, I have an old version of NG's (National Geographic) TOPO with maps for Colorado, it contains what are essentially the old USGS maps (some must be NAD27) stitched together. The instructions for the TOPO app say to use the default unless you have a reason not to (what might that be?), WGS84, which is a bit confusing being that the content contains some maps with NAD27. Unlike the printed versions of 7.5 minute paper maps, TOPO's stitched, digital version don't specify the datum but they are definitely using some of the same dated, paper maps I've used for some of the map imagery content in TOPO. I'm wondering if these NG TOPO maps are tweaked to facilitate WGS84 or NAD83. When I overlay a map using NAD27 into Google Earth, am I not essentially performing such a 'tweak', to get it to line up with WGS84 (or what4ever I have it set to in Google Earth at the time)? If you know, how far apart are NAD27 and WGS84? I've just started looking into this issue after years of casual GPS use for backpacking but I've always been curious about it and would like to learn more. Are there any resources (websites) you'd recommend that can provide more insight on this?
