Hand Held GPS 1

[BigH]

I'm getting tired trying to figure out non-existant marked chainages on my long road job. You see something that has to be noted and it is difficult to get the exact chainage at a glance. I would like your feedback on a personal hand-held GPS instrument - one that would get me to 5m or so (not so critical now but maybe later) with some elevation accuracy as well. Make and models wanted! Your help is appreciated. Remember that this is on "my" cost.

 

[TTK]

I highly recommend the Garmin eTrex line, and I have been very happy with my Legend model.

Make sure you get a WAAS enabled version if you are looking for 5 m accuracy in a handheld.

 

[eric1037]

I'm not at all confident of the elevation accuracy of any hand-held unit.

As for the spatial accuracy, I have had good experience with the Garmin III Plus. They also have a beacon that you can buy to increase your accuracy.

 

[GeoPaveTraffic]

I agree with TTK, the Garmin eTrex is very good for general use, +/- 5m should be no problem at all. As for elevation, don't rely on it as it could be off by several 10's of meters.

 

[Focht3]

BigH - WAAS probably isn't available in India! It's used in the U.S. near airports - to improve the GPS accuracy for airplanes landing/taking off. It's pretty useless if you are more than about 15 or 20 miles (25 to 32 km) from a WAAS-enabled airport. Without WAAS, the GPS accuracy isn't too hot. But it is still handy, particularly when used in conjunction with your digital camera.

I have a Garmin GPS V - I love it. My typical accuracy is on the order of 5 to 15 meters. I seldom get much 'time' below 5 meters.



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[TTK]

Focht3:

I think you may be confusing LAAS for WAAS. WAAS does have a somewhat limited availability because only two correction satellites exist (one for each hemisphere). If you can see this satellite, then you can get WAAS level accuracy. I am able to achieve sub 5 meter horizontal accuracy about 90% of the time.

Here's a better decsription of WAAS that I found on the web:

Wide Area Augmentation System

WAAS is part of the FAA's plan to retire the existing use of VOR, NDB, ILS, and LOCALIZER aviation navigational systems. WAAS is designed to improve the accuracy and ensure the integrity of information coming from GPS satellites. WAAS will provide accuracy performance of 1 – 2 meters horizontal and 2 –3 meters vertical throughout the majority of the continental U.S. and portions of Alaska.


How it works

WAAS works by providing a series of ground stations that receive GPS signals and transmit corrective information back to another satellite that then provides that information to your GPS receiver. This correction is needed to correct timing errors caused by signal propagation thru the atmosphere and other facts that change the timing of the GPS signal.


Other systems

There is another augmentation system called LAAS. Which like WAAS provides a corrective signal but this is done over a much more local area via a line of sight radio link VHF. This is a short range system just for use around the airport environment.

This system is designed to provide ILS like capabilities to aircraft.