GPS and surveying

[California]

Highbeam, or anyone:

Can you use a hobby GPS to project the extension of a known line? What I mean is to zero the device at a known front corner and at a second point on the side line, then continue on through brush to mark the side line clear to the back corner of the parcel. What sort of accuracy could I expect a thousand feet beyond the last good monument?

Any advice on a suitable inexpensive unit?

 

[Fungus]

What I’ve learned is that the deed property description is derived from the county plat on file. Sometime this process introduces omissions or errors because the person doing it is not checked. I found this out the hard way on 14-acre piece of property I’m developing.

Anyway, the surveyor’s meets & bound description is a relative coordinate system based upon some township & range reference. There is no way to cleanly go from this grid system to one based on a sphere such as longitude & latitude. Perhaps there is some sophisticated software that can do it, but like you, I just wanted to keep it simply and use the tools I have.

When I’m contemplating a piece of property I always enter the M & B bearing info into AutoCad to check closure and area for accuracy. Once I’m happy with this you can use AutoCad to report all points as XY coordinates (in meters) from the POB.

Usually the POB is clearly marked so I now know from this point how many XY meters each point is. If you switch your GPS to UTM mode it reports position as XY meters – nice. Then I read the UTM position of my POB and simply add the offsets of all my other points to it. Now I have a list of UTM waypoints that I can enter into the GPS to form a route.

For larger properties this works for me and I can get within 20’ of the pin – usually rebar stuck in the ground.

 

[Highbeam]

"When I’m contemplating a piece of property I always enter the M & B bearing info into AutoCad to check closure and area for accuracy. Once I’m happy with this you can use AutoCad to report all points as XY coordinates (in meters) from the POB.

Usually the POB is clearly marked so I now know from this point how many XY meters each point is. If you switch your GPS to UTM mode it reports position as XY meters – nice. Then I read the UTM position of my POB and simply add the offsets of all my other points to it. Now I have a list of UTM waypoints that I can enter into the GPS to form a route.

For larger properties this works for me and I can get within 20’ of the pin – usually rebar stuck in the ground."

That's what I said, but not as clearly I suppose. It can be done and the accuracy 1000' down the line is the same as right at the beginning since it is limited by the GPS. I use the autocad to help with the geometry but in the olden days people did it by hand.

Northings and eastings, coordinates, xy meters, they are all the same thing in function. You want the GPS unit to be readingh off changing coordinates as you move. Whether you move in a straight line or not doesn't matter since you are trying to get to a calculated coordinate. Kinda like a treasure hunt. Trying to find a point is what we call a "point monkey" in the business since it is pretty simple once you know the coordinates of your destination.

Trying to find an old corner in a 20' radius is not that easy. I have spent hours stomping around an iron pipe corner without seeing it until the metal detector came out.

 

[BlueRidge]

<font color="blue"> We use both meets+bounds as well as the township and range method in Washington. Meets and bounds when the parcel is of goofy shape. T&R when it is a square chunk that was sectioned off of a larger chunk. I do not think it is an east west thing. </font>

It is, for the most part. There are always local variations. Your variation is probably the most common. It's funny to see property descriptions in T&R that are trying to describe some wacko shaped parcel. It can get quite convoluted!

 

[thcri]

Code54,

send me your cordinates of your property and I will send you back an aerial view of your property. PM them to me


murph

 

[Jstpssng]

A little late but...

We use those "Hobby" GPS units for timber cruising and harvest layout. However, they aren't accurate enough for surveying purposes, no matter how long you let them average. There are too many variables,as the satelite signal is distorted by clouds, nearby tree canopy, and other interference. A "survey grade" instrument will adjust itself by comparing readings taken from a nearby site with known coordinates; even then, (Like a total station, transit, staff compass, or...) they are only as good as the person using them.

Also, as landowner you should have the original copy of your deed; this will be the same as any government agency would have.

 

[bdog]

</font><font color="blue" class="small">( Highbeam, or anyone:

Can you use a hobby GPS to project the extension of a known line? What I mean is to zero the device at a known front corner and at a second point on the side line, then continue on through brush to mark the side line clear to the back corner of the parcel. What sort of accuracy could I expect a thousand feet beyond the last good monument?

Any advice on a suitable inexpensive unit?

)</font>

Get a Garmin. I have 76s map and it works great. Has all the features you need and then some.

If you know that lat/lon of these two points and key them into the gps and then project the the line 1000 feet or 10,000 feet you are going to be within 10 feet or so.

I am not a land a surveyor but I do seismic surveying all the time with GPS. We use Trimble RTK surveying packs that have 1" or better accuracy in X,Y, and Z. With the garmin unit operating in WAAS I have checked it against the trimble and have always been within 10' on x/y but elevation is horrible.

anyway, I am not sure what you are trying to do. If it is building a fence or something definitely get a surveyor out there to be sure. Otherwise I would think you could use a hobby unit with WAAS to get you within 10' or so.

 

[TC18guy]

A LAND SURVEYOR'S THOUGHTS:

The above posts describing the map calls as bearings are correct, they are not LAT/LONG coordinates. The bearings are normally relative to some definition of North. Sometimes that is from an old legal description or nearby plat, sometimes it is magnetic, astronomical, or even assumed. To a surveyor North is relative for any individual piece of property and true North is generally not that important. If two adjacent properties are examined, then one properties bearings can be rotated to match the other by subtracting the bearings on a common line.

The best use of a handheld GPS would be to use it as a compass in conjunction with a measuring wheel or fiberglass reel tape to get to the next point. Using a hand held GPS for line clearing is probably a bad idea. If you assume your handheld has an accuracy of 20+/- feet and the known section of the line is say 400 feet long, if you were to extend those coordinates with the GPS another 400 feet your accuracy drops to 40'+/-.

Averaging a handheld GPS over a point for a long period of time is pointless. The largest error with any single GPS unit (without the benefit of RTK corrections) is due to atmospheric conditions. No amount of averaging is going to compensate for this.

The T&R system is called the Public Land Survey System. To my knowledge, the PLSS exist in most parts of every state except some of the original 13 colony states. The surveys of the public lands divided states into township (usually 6 miles square and were designated by town/range) and divided the townships into normally 1 mile square sections. Metes = direction & distance, Bounds = layman call such as trees, fences, adjoiners deeds, etc. Some descriptions are written metes & bounds off of the section's corners and some descriptions are written to fractionally divide the section into halves, quarters, etc. Descriptions for states that do not have the PLSS are usually written Metes & Bounds off of some known control marker.

CODE54 as long as you and your neighbors agree on the corners then there should not be a problem, but not all banks require surveys as part of a typical home closing. Their only interest is that there are not any major encroachments or deed problems that would affect the value of the property. This can be checked WITHOUT a survey. Surveyors are the only professionals that can accurately translate a legal description or plat map to the ground. There are no other governmental or other agencies that can help you with that unless they staff surveyors & survey records. Even so they won't do it for free. Around here $1800 would figure for about 2 full days of a 2 man crew to work in the field plus some research, computing, and drafting time. Surveyor's GPS does not work well in the woods (and not everybody has it) and so the survey might have to be done using line-of-sight methods.

I field several calls a day with the same questions you are asking. They are good questions, but the answers will probably very depending on your specific location. Your best bet is talk with your local surveyor.

 

[California]

Thanks everybody for an enlightening discussion.

I concluded that the precision of hobby gps wasn't close enough.

I needed to find the point where a haul path crosses on a slight diagonal into my part of the orchard. For 50 years these two adjacent orchards were managed jointly so to the casual visitor they appear to be a single parcel. Until this year a verbal agreement about who harvests which row of apples was sufficient.

Now I'm getting tired of recreational users who cross into my orchard and sometimes continue as far as my barn, but I didn't want to offend the neighbors by unknowingly setting a marker that encroaches on their side.

The parcel on the opposite (east) side was sold last year and I found sufficient formal survey marks along that line. So I bought a cheap HF fiberglass 100m tape, lashed my 100 ft tape onto its tip, and measured across my parcel from the good markers on the east.

My first measurement hit 10 inches from the fence that goes a third of the way down my west boundary so I measured across from the other two good east-side points. These three new west points fell in a perfect line so I set monuments, then sighted a fourth point to project the line to where it disappears into the canyon.

I'm convinced the line I ran is within a foot of the true boundary.Now when I meet a stranger in the back of the orchard I can point to the t-post they must have seen if they got that far. Finally, I'm seeing fewer footprints (human, equine, dog, atv) back there.

 

[Code54]

Thank you once again for all the infomation. Sorry it took a while to respond I did not have an internet connection for a while and I been working on the house for what seems like 24/7 ...
One of the neighbors parents built my house so he knows the propery very well and has offered to take me for a walk and show me the markers so that should be a BIG help. I have also found 3 of them on my own so far. I now am walking to them and saving them on the gps and recording the lat/long just in case a tree takes out the marker so something.
Thank you once again and sorry for the delay responding!