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# Etrex used for simple surveying

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I have a Garmin Etrex that I use when Geocaching. In my business we are starting to do a good bit of wireless Internet installations, which involves lining two antenna's up precisely, or pointing one in the fairly precise direction of another that is omnidirectional. So, my question is this:

Will the Etrex serve me well as a basic method of surveying the area for this? For instance, this is what I am trying:

1 - Mark point A

2 - Mark point B

3 - use the goto feature to get distance between the two as the crow flies (or the satellite in this case!)

4 - check the elevation (this part I am not sure can be relied upon) and figure the difference in height

5 - Using the above info, calculate the degrees needed to point one antenna at the other accurately.

I am brand new to this stuff, so I am still learning and have much to learn yet. Let me know if this will/will not work or if there is an easier way, etc.

THANKS!

Geo

Without knowing the level of precision you need, this is a hard question to answer. It also depends on how far away the two antennas are located. If they are within a few hundred feet, then your precision will not be very great. With longer distances it will be easier to hit more closely to the mark.

You can sort of eyeball the precision you are getting by remembering that the eTrex will get you within 15 meters of your "true" position about 95% of the time. (Higher quality--and more expensive--survey-grade receivers could get you within a few feet.) You can plot out a ring of this radius around your antenna locations and calculate the range of angles that will get your antennas to line up. This might at least help you get started.

As for elevation, I would plot your antenna locations on a USGS topo map rather than rely on the elevation reported by the eTrex.

Thanks Moun10Bike! These situations will typically be around 500 to 2000 feet. The distance part works great, I just wondered mostly about the elevation, and if my way of doing it was sound.

I noticed when I tried this the first time, that the elevation showed point B as being 22 feet higher than point A, yet Point A is up a slight hill from point B. This seemingly incorrect reading could just be my lack of knowledge with the elevations stuff on a GPS.

Thanks!

Geo

I'm not surprised at the incorrect elevation measurements -- the GPS system is roughly 3 times less accurate in the vertical plane than it is in the horizontal plane (i.e. you can expect only about 45 meter accuracy 95% of the time vertically vs. 15 meter accuracy horizontally). Altitude based on barometric readings will be more accurate than this, but then your barometer needs to be repeatedly calibrated from known elevation. I'd tend to use the topo maps for greatest elevation accuracy.

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