Hello everyone.
I have a great deal of experience in determining approximate coordinates for property corners. Note that there are two sources of error.
First, can you see good evidence for all of your property corners on the Google aerial or do you have to guess at the location for one or more corners?
Second, do you know how to operate your GPS in order to maximize its accuracy? Below are some more thoughts on this point.
All
dedicated GPS units use WAAS technology. There are 3 WAAS satellites that cover the USA. Your dedicated GPS can most likely only see one of them.
IF (1) your GPS can maintain a lock on the WAAS satellite serving your area and (2) there is a good satellite constellation, then the best accuracy you can likely expect is around 15 feet.
It is common to lose lock on the WAAS satellite due to heavy forest and/or terrain masking. If you lose WAAS lock and there is a poor satellite constellation then the accuracy of your dedicated GPS can easily drop to 100 feet or worse.
Be sure you know how to tell if your GPS has a lock on the WAAS satellite serving your area.
Some current Garmin GPS units can also get data form the Russian
GLONASS GPS satellites. More satellites = more data = better accuracy. If your dedicated GPS loses lock on the WAAS satellite serving your area but your GPS can use GLONASS data, then you can still get accuracy of around 15 feet.
Mobile devices (smartphones, tablets, etc) do not have WAAS. Unless the GPS chip in your smartphone etc can use GLONASS data, your accuracy is going to be around 50 feet
at best.
The iPhone 4s and newer models can all use GLONASS data. Many (but not all) Android units can also use GLONASS data.
Thus, there are 3 options:
1. Older GPS with WAAS
2. Newer GPS with WAAS and GLONASS
3. Smartphone with GLONASS
For the best accuracy, my recommendation is to pick #2 or #3. If you go with option #1 then be sure to use one of the websites that predict when there will be a good satellite constellation.
For more information, I have published several articles geared towards using GPS technology to locate approximate property corners. You can find them at
http://www.propertylinemaps.com/p/plm_gps_tips.html
Also, I have produced an
enhanced Google map viewer called Gmap4 that includes high resolution topo maps, geolocation and various other features. This project is part of my way to "pay it forward" and is used by people that enjoy a wide range of outdoor activities.
Since Gmap4 runs in your browser, you start it just by clicking/touching a link. If you open any Gmap4 link on your smartphone and then touch Menu ==> "My Location" then the map will center at your position. Touch the symbol to see your coordinates. That symbol will follow you as you move and the map will shift as needed.
Gmap4 provides full support for
MGRS coordinates. Find that feature under the Menu button.
The Gmap4 homepage has a FAQ, examples, quick start info (on the Help page) and more to quickly get you up to speed.
One of the articles on the Help page shows you
how to use Gmap4 on your smartphone offline.
Gmap4 default map: http://www.mappingsupport.com/p/gmap4.php
Gmap4 homepage: http://www.mappingsupport.com/p/gmap4.html
Joseph, the Gmap4 guy
Redmond, WA
