PDA

View Full Version : Surveying with a GPS?


jamesq
February 06, 2006, 00:48
a friend of mine just bought some land, and it seems that the neighbor (who only purchased the land next door about 6 months before my friend) is trying to do a land grab with about half an acre. the land in question is hilly and tree covered so line of sight would be near impossible.
anyway, i was driving the other day and i noticed a surveyors office that had a large sign that listed 'GPS' as one of the services offered. i thought 3 meters was as close as GPS was capable of.
he has map coordinates of what he was sold.... does anyone have any experience with surveying? is GPS just for ball-parking it?

Dave1
February 06, 2006, 01:24
Personally I don't think GPS is close enough at all. Best I ever got out of mine was 16 ft. That's diameter. They surveyed my parent property and they were off A LOT! Seem the rectangle property suddenly turned itself into a trapizoid??? Shop around for a recommended surveyer with references. You'll be happier in the end.
Just my .02

Dave

instr8
February 06, 2006, 01:31
One of my newer clients is a surveyor. He mentioned GPS surveying the other day wanting to know if I knew the specifics of how it worked, unfortunately, I didn't but from little bit he talked about it I assume it is coming down the pipe and will soon be commonplace in that profession.

ACK
February 06, 2006, 01:55
Not your typical GPS (http://www.trimble.com/trimbler8gnss.shtml)

A surveying GPS is considerably more accurate than our handheld/auto units.
Download the data sheets, some of this units clain an error of .25 m = ~10 inches. In some cases 5 mm!

We use GPS for geological studies, in CA they are used for earth movements (faults)

ACK

Windustsearch
February 06, 2006, 10:07
Surveying with a GPS usually involves a Trimbel backpack unit or the like. It is very accurate.

Bwana John
February 06, 2006, 11:38
Originally posted by Windustsearch
Surveying with a GPS usually involves a Trimbel backpack unit or the like. It is very accurate.
We try to create a new GPS point on every new survey we do, and then tie that new point into all previously surveyed points and monuments. We use the Trimble. I usually trust the GPS points over previous rod & chain type surveys. I would not trust a handheld unit for an exact boundry, and even just using it to ballpark make sure the unit is set up correctly with the right datum.

ACK- What program are you doing geologic mapping with, ArcView? These new GIS programs are really somthing. It used to take years to make a TIN without them.

G21A
February 06, 2006, 12:43
While regular GPS receivers are usually only within 30 feet or so, some places provide GPS enhanced signals for aircraft to use for flying approaches. Obviously they have to be very accurate, so what they do is combine the dynamic GPS data with data received related to a point of known co-ordinates and then apply the appropriate correction to the dynamic data. This takes out the government induced "correction" to the data and makes it as accurate as the mil-spec data.

Survey Punk
February 06, 2006, 13:47
Trimble user. Depending on occupation time at a station you can get down to .02 foot, roughly 1/4 inch. Doesn't work under tree canopy, though.
Don't have line of sight? Can you say BUSHAXE?:biggrin:

JB

ftierson
February 06, 2006, 14:16
As others have mentioned, with the correct equipment (that includes an established base station), GPS surveying units are extremely accurate...

We are using GPS units more and more in archaeology, both because of ease and accuracy.

I've seen setups were you could recognize being "off" by 2mm (that's 2mm, like in 0.078 inches!)

When everything is correctly done, the cumulative GPS accuracy beats conventional surveying equipment, and you don't have to brush out for line-of site from transit to target and set-up all those extra times (with the slight error involved in each set-up).

But you don't do any of this with a $200 hand held GPS unit, either...

Forrest

hydrotx
February 06, 2006, 14:24
I believe that differential GPS is the only way to get the sort of resolution you would need for serious surveying applications.

Regards,
Joel

raeldridge
February 06, 2006, 17:00
GPS surveying is light years ahead of the rod 'n chain method.

my dad went through this several years ago. not the problem with his neighbors fortunately, but getting a surveyor for the land.

he has 150+ acres in eastern KY, of course there's only 14 of those acres that are actually level. (and not covered with briars, trees, scrub brush, etc.)

young man (as may dad told me) did his farm in about a day and a half boots on the ground. then the surveyor spent the rest of the week at the courthouse and the office getting his accurate measurements to line up property lines with the somewhat less than accurate measurements of the old timers.

the crew came back and sunk surveyor's rods, dad supplemented that with concrete posts set level with the top of the ground at various locations also.

dad said he went around to all his neighbors, said he was doing this if they wanted to get in on it too, and get a discount since the crew was already there. they didn't, and dad has had to show the marked property lines (his) to several folks already. not in any confrontational way, again fortunately, but it sure would have helped everyone if they had had a little foresight.

get it done, there's no way you're going to regret it. and God forbid, you get in some urinary liquid distance throwing contest with your neighbor, you've got the survey on your side.

of course, tell your neighbor you're getting this done, and invite him in as sort of a 'group buy' on the surveyor's time. it will benefit you both, and may stop any arguments right now. ///grin///

mitchellh
February 07, 2006, 15:10
Survey Punk,

Do you have any association with Rivers & Associates in Greenville?

Survey Punk
February 08, 2006, 08:38
Certainly do know about them. Been in the business as long as I can remember. The gentleman who first got me started in surveying, W.C. Rodman Jr. did consulting work for them after he retired from private practice. Greenville is really booming lately and I'm sure they're staying busy.
I'm employed at the big phosphate mine about 40 miles East of Greenville. Still get out and do little things privately just to keep my hand in it.

JB

mitchellh
February 08, 2006, 10:55
Thanks, I was curious. My brother has worked for them since 2004. He's been in Surveying since the early 90's though.

It appears most cities in North Carolina are booming. Heck, same way here in Va. We have rural farm land being purchased for development, for commuters to the metropolis of Va Beach, Hampton, Chesapeake, and Norfolk.

Good luck to you.

Bukaluka
February 09, 2006, 07:01
To answer the original question, GPS will be just fine for your survey as long as you use a reputable surveyor. Being in the civil engineering/survey business for the last 26 years, there have been tremendous advances in GPS over conventional methods. Like everything else, there are times when robotic total stations would be a better choice.

Tree canopy and tall buildings are a GPS nemesis. They tend to interfere with the satellite signals. Our crews are equipped with both and use what is appropriate for the job (singularly or combined).

Like others have said, the accuracy is incredible and the .gov has discontinued corrupting the satellite signals on a regular basis, which used to take us a few days to receive and apply the corrections to our field data.

Richard in PV