Handheld GPS units usable for tract layout???

[dpb]

Tried research what could find on Garmin site but w/ my slow dialup was too painful to delve deeply.

Best I could see appears that WAAS of roughly 10-ft (3-m) is best could hope for. This is, I presume, all any moderate/low-cost device has?

Need/desire is to layout acreages for ag purposes--haying, etc. Need accuracy to roughly 0.1A out of typical 80 to 160A patches. Note that

1A is 16.5-ft (1 rod) by 1/2-mile for thinking purposes. Hence, if 10-ft is best I can find a corner at one end, that's 2/3-rds an acre roughly so really need about 1-ft. One advantage is it's flat, no trees, no other obstructions.

Anybody have any detailed knowledge of abilities of units and how well suited would be to start in a corner of a field and mark a line at other end 1/2-mile away parallel to hit (say) 80A out of a quarter-section (160A). I can locate most boundaries reasonably well by existing roads, old fence rows that are visible if know what looking for, etc., altho there are a couple of places that have now been in grass for nearly 30 years that don't have any visible landmarks any longer between quarters that were all farmed together and now can't find specific location of half-mile lines as no corner posts or other landmarks remain. Field technician from FSA (Farm Service Agency) came out w/ their high-priced system last year and marked one of these corners for me; he brought his Jeep Wagoneer. We got out to place the stake and probably less than

20-ft from it turned around and couldn't find it in the grass... :) Not much of it is that tall, but that quarter was last year; we made over 400 large round bales off a little under 80A.

Anyway, any input appreciated...

The ag manufacturer's tractor-mount systems are 6" or so, but they're also multi-k $$ and this function doesn't need the ancillary crop software, etc., just waypoints...

[HeyBub]

On AVERAGE, you can get a precision of ten feet. You might get down to a couple of feet if the GPS unit can see five or six satellites. Precision is improved by letting the unit remain stationary for up to several minutes. With an abundance of satellites and a ten-minute equilibration, you might get as precise as 0.1 meter or 3 inches.

The military is in the process of launching a set of satellites that will give precision down to a minimum of ten inches.

[Ed Pawlowski]

You can get better answers on the Garmin newsgroup. There was just a thread about accuracy. Garmin does say about 10' from what I recall and some posting did better, others not so good. I've seen whee they use GPS systems for harvesting so the accuracy you need must be available at some cost level.

[dpb]

Ed Pawlowski wrote: ...

Yes, the guidance systems are 2-3" but they're a $20k+ add-on.

That's not the purpose for this nor can justify that outlay for the purpose.

Since I've found some other handheld units for the ag market that are reasonable and software more in the budget...I might just bite at $500 and try it out and then get FSA to come double-check one or two fields to get a feel for how well it's doing...

Any other input anybody does have would be interesting...

[trader4]

Just out of curiosity, why do you need accuracy in plot layout to a tenth of an acre on an 80-100 acre plot? That's .1% accuracy, which seems extreme for common agri plot sizing.

[Pete C.]

It seems to me that you need to first clear the grass down to levels that don't hide vehicles, and then get your FSA buddy in to locate the boundaries so you can place permanent and easy to locate markers. Once you have those points located, you can pretty easily work off of them with a large reel tape measure, or a nice laser ranger. If the markers are not more than 200' apart you can use the inexpensive Stanley laser ranger with it's 100' range. Moderate priced rangers go up to about 600' range. GPS might be useable in the future with upgraded satellites, but it probably isn't good enough now with just a handheld receiver and no fixed correction station like the expensive units use.

[dpb]

[e-mail] wrote: ...

That's consistent w/ FSA measurements for compliance; of course, they have their USDA-issued devices that I've no idea what cost. If there's an overage, one can be penalized so it is advantageous to be accurate. It didn't use to be so much an issue before the GPS-based surveys and

4-wheelers; now they monitor much more closely since have the facility to do so as compared when they had to use the old measuring wheel or chain.

Realistically, if within about an acre would be adequate; what I was thinking is that if, indeed, the waypoints are 10-ft off in worst case that could be nearly 4A in the total aggregate if each side happened to stack up wrong. And, of course, there are other fields that are full mile in length and the 1 rod equates to 2A over the length so a few feet can begin to add up to measurable difference fairly quickly.

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[dpb]

Pete C. wrote: ...

The point of the measurement is to lay out for haying. Clearing the grass first rather defeats the purpose... :)

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[gpsman]

Any WAAS-capable unit is going to give you horizontal accuracy of =B13m,

99% of the time. =B13m does not disclude accuracy of =B13mm, but you're usually going to get somewhere between those 2 standards which seems as if should be adequate for your purposes.

You could probably use MS Streets & Trips to delineate and print your areas of concern, for no more than 40 bucks.

Just about everything you could ever want to know about gps:

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- gpsman

[JimR]

If it's essentially a one-time use, consider renting a Trimble back-pack unit for a day or so. In a recent trial here, we located rare plants -- seedlings -- that were going into the ground, for which we needed continued historical data (e.g., seed source, growing medium, transplant success, etc. We GPS'd 700 plants, most of which were at most 2 feet apart and came up with a plot using Arcmap that shows each individual plant in a small area about 30' x 30'. Now we can go back to individual plants and measure their growth, vitality, etc. (A previous planting tried using plant tags and small flags to identify each plant, but neighborhood youth discovered the site, picked up the flags, and moved the plant tags around, which meant the group lost all of its records for individual plants.)

[dpb]

JimR wrote: ...

If successful, it would be useful every hay season because we don't hay the same areas each year.

Which Trimble unit was it? The Juno is what I was looking at I mentioned above as reasonable for the purpose. But, in looking further it appears it has no useful software in the base product; that seems to be $2K start point...

Do you understand what is in the base unit vs the added software?

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[hrhofmann]

Any chance of measuring the extreme points and then dividing it up and double-checking those mid-points for accuracy. That giives you less chance of an accumulating error.

[Dean Hoffman]

Any chance of getting a bored, local farmer with with the fancy guidance systems to help out? There are some hand held laser type measuring devices available too. I can't remember any brand names off hand. Would it be worth while to buy a used total station on Ebay then resell it when you're done?

[dpb]

Other than the time of backtracking and extra driving thru the fields, not really. But, time is time and fuel is fuel. Remember it's a full half-mile minimum from one end to the other and the it's fairly slow going as these are heavy, clumping type grasses so it's not driving up and down a country lane. The full-mile rows take a while even in the pick'em'up.

That's part of the difficulty in laying out w/ the wheel; it tends to be short owing to the hummocky nature of a path thru field as compared to an end that does abut a road or service path that can roll down (altho they're the exception rather than the rule as there are not roads thru most section lines).

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[dpb]

They're definitely not bored this time of year... :)

I'll use anything enough to be worth a certain amount (just not $20k :) ); no handheld laser will make a 1/2-mile and there are too many places where there are enough rises/draws can't see over that the GPS would have the big advantage if can work out what is cost-effective.

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[trader4]

It's also consistent with big govt stupidity. There is no rational reason that any plots need to be measured to .1% accuracy for any govt program. One percent would be more than enough. But it's what you get when you have idiot bureaucrats making up whatever rules they feel like.

And this is what were paying more govt employees to do. Go break balls of taxpayers by enforcing an obviously stupid accuracy requirement.