Position accuracy with tree cover

[+Cougfather]

Just getting started with this fun hobby. We're in the Pacific Northwest which means lots of trees. We've noticed that when we hunt for a cache under thick tree cover, we have a tough time getting consistent readings on our GPS's. We use a Blackberry phone, an HTC Touch Pro 2 phone and an old Etrex legend. The position readings jump around as the signals get worse. Not surprising since the GPS's rely on "seeing" the satellites. How do the people hiding the caches get good solid coordinates for the postings? Don't they have the same trouble we do under those trees?

Edited September 8, 2009 by Cougfather

[+Indotguy]

Depending on various factors (antenna type is one) some devices perform better under tree cover than others. As for people getting "good solid coordinates" under these conditions, sometimes they don't.

[+Pulvertoastmann]

Just getting started with this fun hobby. We're in the Pacific Northwest which means lots of trees. We've noticed that when we hunt for a cache under thick tree cover, we have a tough time getting consistent readings on our GPS's. We use a Blackberry phone, an HTC Touch Pro 2 phone and an old Etrex legend. The position readings jump around as the signals get worse. Not surprising since the GPS's rely on "seeing" the satellites. How do the people hiding the caches get good solid coordinates for the postings? Don't they have the same trouble we do under those trees?

 

Welcome to this beautiful hobby and welcome back to nature

 

The devices you've used so far are all being outperformed by todays more advanced (and dedicated) gps receivers.

First of all, neither of your units is WAAS / EGNOS enabled, which increases accuracy from 10-15 meters to up to 2-5 meters. Furthermore all your units are using small patch antennaes, not surprising since the gps feature is only a nice addon to a compact device and is intended for car navigation and the like and not for taking precision measurements. The eTrex Legend is an exception to my last statement, but it is still outdated.

 

To give you an Idea about how big the difference is:

My Garmin GPSMAP 60CSx provides me with 5 meters of accuracy in deep forests, in situations where my symbian cell phone wouldn't even get a satellite lock, not even a very bad one.

 

Units like the 60CSx have a quad helix antenna, high sensivity gps chip and advanced algorythms to filter the gps signal to make it less "jumpy".

Dedicated gps receivers provide an averaging function, which means you lay down your unit and let it take hundreds of measurements which will be averaged to reduce errors from bad satellite constellations (which will change constantly while the averaging is in progress)

 

Even with a good gps unit we're still talking about probability and statistics here and not about absolute measurements. There is ALWAYS an error in the measurement which is immanent to the system itself. For this reason experienced cachers will return to the site of their new cache multiple times and retake measurements and average them manually to further reduce the errors introduced by bad constellations (this may be necessary under difficult conditions like in dense forests only).

 

If you consider to stick with this hobby (something I can only recommend) I suggest that you start looking for a good advanced unit. Common choices are the Garmin Vista HCx, the Garmin GPSMAP 60CSx (which I own and which I love), the Garmin Oregon line of units, the DeLorme PN-40.

 

Which one you choose depends on what you expect your unit to do - some units (like the Oregon or the PN-40) offer paperless caching functionality which means they store all the information like cache description, hints and recent logs for a cache, but they are quite expensive.

Other units like the 60CSx are a little less expensive, and especially the 60CSx is considered by many to be a true workhorse and one of the most accurate units on the market. It lacks the paperless caching functionality however. Since you're using smartphones this may not be too much of a loss for you, since there are good applications for smartphones to manage your cache informations.

 

Please browse through this forum for more in depth reviews and buying advices, this topic has been discussed a thousand times

 

best,

Pulvertoastmann

[+Redwoods Mtn Biker]

The biggest difference on newer units is the high-sensitivity chipset. Having one of these will totally change your experience under canopy.