I am going to buy a GPS in the near future. I will be using it for horizontal and vertical control. Narrowed my choices down to PM2 and Topcon Hyper. I'm trying to decide if I need L2, OPUS solutions would be nice for a check. What system does Thales make that has L1/L2?

Thanks
Jake

The impression I get from this board is that a lot of surveyors don't have "readily" available GPS quality points available nearby.

When that's the case, I'm assuming that L1-L2 units work much better than L1 units(very long baselines).

Where I'm at, in northern Ohio, we have about 2-3 miles spacing of GPS quality stations. I use L1 units exclusively and get very, very good results.

Ashtech Z-Xtreme, L1/L2. You can buy it without L1/L2 processing software, so you are committed to OPUS or third parties for solution. Can Analyze the L1 output right alongside your PM2's with the L1 Solutions software. When you want to upgrade and solve it yourself, buy a hardware lock and you are in business.

Buy 1 dual phase unit and 2 or 3 PM2's.
About 14-16k or so.

I'm surprised no Ashtech people responded to you yet.

Paul in PA

John,

That's our problem here in southeastern Oklahoma. ODOT did make a pretty good HARN network, but in our county we only have 2 and they are 34 miles apart. So they're too far for us to use in most of our 35mi by 35mi area. We've basically had to create our own personal HARN network off of nearby HARNs and CORS. Once we're done we will be within 12 miles of any control point. This will allow us to use L1 on any job we will ever do. Thank God ODOT has added 3 CORS to our area and 2 more on the way. Now if Arkansas Highway and Transportation would get in gear maybe the east side of our network would be better.

Jacob,

I would seriously look to see what kind of HARNs and CORS are in your area. If you are within 12 miles of B-order or better control from your work area then PM2(L1) should be good enough. If you don't have good control in your area, then you will probably want to establish control using the Z-Extreme(L1/L2) either by using OPUS or CORS data. We opted for the latter. OPUS is a great tool and is good for checking your work, but like Phil Stevenson of Ashtech has told me many, many times "OPUS is not a substitute for a GPS control network". Click on the link below for more of his thoughts.

As for my thoughts on Ashtech versus their competitors, I have no reference as we only use Ashtech. However, I will say that I can't conceivably see any company approaching the support that Ashtech gives its customers. We have 3 receivers that are 4-5 years old and they still support us and on a toll free to boot! In fact, I talk to Phil pretty much once or twice a week. And when he's not there I get great service from Linda and others as well. Topcon's prices may look attractive, but remember that part of that price is support. So if you plan to be using them for many years to come, it will be a very important part of your decision. Currently we're looking to sell our old receivers and go with new ones. That is once our network is done. And when we do I couldn't see us going with anything other than Ashtech and their PM2s. Good luck.

http://www.i-boards.com/bnp/pobtha/messages.asp?MsgID=7190&ThreadID=1291#7190

Tommy McClain

Modified By Tommy McClain on 7/8/2003 at 6:18 PM

If I suffered that kind of spacing, I'd hire a company(with a group of surveyors) to come in with top-notch equipment and GPS some well-placed monuments, maybe even the county engineer might be interested in a few monuments. We had some placed at $150 per monument. That way you(and your group of surveyors) could be certain to put the monuments in a good, open and SAFE(relatively speaking) position.

That would be a lot cheaper and then instead of getting two PM2's and a L1-L2 unit, you could get 5 or 6 PM2's.

Hiring another company to do our own survey work would be blasphemy! ;) There's maybe 2 other competitors in our area. One is in state and he doesn't have GPS. The other has GPS, but is in Arkansas. Anyway, the nice thing about doing it ourselves is we can spend how much time or money we want on it. And when we get it done, it will be something that we know is done the way we wanted.

We've been using highway right-of-ways. In our area we have a lot of 2-lane highways where they either purchased enough right-of-way for 4-lanes or they placed a new highway next to an old highway or railroad. So we've been putting of monuments on top of cleared hills where we have excess right-of-way. We've set about 11 monuments so far and we have 3 more left to set before we finish the network. 6 of those will probably be used only as secondary control points that are used to make the network more dense. We've been working on it for the past year in our spare time just using 2 Z-Surveyors and a one man crew. We've been getting 2 hour dual sessions per vector between our new points and HARNs/CORS. It should be quite nice when it is done. When it is, I'm sure we'll buy 3 PM2 units for one conventional crew and possibly 3 more for another conventional crew if we need them. Anymore than 3 on one crew would be way more than we need.

Tommy McClain

With an L1 system like the PM2's, if you don't have existing control in the area, is still possible to set local control? It will not be tied to any datum but it should still be correct relative to itself. It would be nice to be on a datum if your near control, otherwise just assume a coordinate system. Can this be done or am I missing something?

Jake

Excepting the assumed datum, I've been asking myself that question for 4 years now.

The PM2's are very accurate and when I check on our network, I usually check with 1/2" or less in about 3 miles, but the accuracy(maybe I should say precision) drops to about 3"-4" in about 6-7 miles, which is still extremely good in and of itself.

I've gotten the impression that L1-L2 units will give better results, but that's a self annointed assumption.

The Promarks claim an accuracy(and I'm guessing at this) 1cm +/- 1(or 2) ppm. Are L1-L2 units any better?

Jake,

Yes, you can set up a "local network" that has no "ties" to any datum. Just pick the NAV position of one of your setups and put together a network. Probably the biggest misnomer I have had to attempt to explain to others is that even though I am getting "centimeter level positions" they are positions relative to each other. IN your case, I'd go with geodetic solutions and then a custom grid---definitely don't create "pseudo" state plane coordinates without a tie to known "good" control.
As far as "good" control I'd stick with published NGS control in your area. So first thing I'd do ifin I were you would be to get online to the NGS website and perform a search for local control via the data sheets retreival. See what is out there. Print out the data sheets and hit the field to see what you can recover. May be that you find a dual frequency receiver and OPUS could complement your L1 ProMark2's later on down the road.
And I have always contended that hardware and software are one thing, HOW it is supported is a whole 'nother. In that regard I don't think, no, I'll be willing to bet you won't find better support than the folks at Ashtech/Thales have given us.
Modified By Dave Huff on 7/8/2003 at 9:47 PM

Sorry, was travelling all day yesterday and didn't/couldn't check the board.

Our dual frequency product is the Z-Xtreme. For static work, it is spec'd virtually the same as the ProMark2.

With kinematic you have better specs with L1/L2 receivers, and of course you do have the ability to do RTK with a Z-Xtreme.

For static work, of course, you can solve much longer baselines with a dual frequency receiver, and have the OPUS service available as well.

We have an "OPUS" configured Z-Xtreme that is priced very attractively, $8950 for the receiver and antenna.

We do sell lots of these in conjunction with 2 and 3 receiver ProMark2 systems.

Any more questions, please call or email.

Thanks everyone.

I'll be putting in an order for 3 PM2's today. I love playing with new toys. Downloaded the instruction manuals last night.

Let the games begin!

Jake
Modified By Jacob Staff on 7/9/2003 at 10:23 AM

Good move on the 3 versus the pair. You will be much more productive. I've got 9 receivers of 4 different types. A fire extinguisher next to the PC 'cause it can look pretty brutal when Solutions is processing all that "mixed technology". But it handles it like a champ.
Get yourself a new coffee maker. If you don't drink coffee start acquiring a taste for it. Make sure JD gets your address to sign you up for the ORGI gang ;)
If you like learning new technology (ok, playing with new toys) then believe me, you are in good company! Congrats!