GPS 315.....Elevation question

[Guest White Rabbit]

How do I go about setting my elevation? I was hunting the other day and I noticed that my initial setting was at 0ft. I know that where I was standing (in front of my house) was about 40ft in altitude. I didn't mind it that much until I went out on my first cache hunt. It said that I had to be at an elevation of around 160ft. Well, the point was in a building and I got to the top of the roof and my GPS only said 120ft or so. I was in the right place and I found the cache after a bit, but it would be nice to be able to set the elevation correctly. Especially when I go out in search of the one said to be 7000ft up on Mt.St.Helens later this month. Thanks.

[Guest mcb]

You should not have to enter the elevation at all. Your GPS should figure that out on its own. I know that some Garmin unit will let you enter and elevation to help get a lock if you only have three satellite in view. If you have four or more satellites in view they the GPS should calculate the altitude along with the horizotal position. Make sure you give you GPS a good view of the sky and check to see how many satellite it is talking to.

 

Good luck

mcb

[Guest arffer]

Wow, a cache that requires elevation as part of the waypoint?

 

The 315, like all GPSRs, requires at least 4 birds to be locked in to get elevation. Once you have at least 4, you don't have to enter anything, there is no 'calibration'.

 

Here is the reason for my surprise related to the cache you were hunting. Elevation is the least accurate part of GPS. I don't mean just a little less accurate, I mean A LOT. If you can get a few birds locked in that are directly overhead, the accuracy will be better, but frankly the elevation feature is of minimal use.

[Guest Olar]

I had a good example last week with my Mag315 when on vacation in the Dominican Republic. Marking a waypoint on the resort beach without a good sat. lock and no averaging showed as 15 metres(way off). Two days later on a sandbar island not far from the same beach, with numerous sat. locks and 2 or 3 minutes averaging, I got an elevation of 1 metre.

[Guest Kerry]

I suppose the unknown thing with heights (related to sea level) is how good the implemented geoid model is for determining altitudes (sea level) from GPS heights based on datum.

 

With standard GPS I would say they are for interest only.

 

Cheers, Kerry.

[Guest White Rabbit]

Ahhh....4 satellites. I think that was my problem, because I could hardly get 3 in front of my apartment (downtown). The only reason that the cache told me an elevation was because it lead me to a parking garage with about 10 stories of parking. The elevation clue was just telling you to go to the top of it basically. Thanks for all of your input, I thought I was doing something wrong.