I have a project that I may need to located about 4000 water services. I just bought the PM'S and am wondering if I can send 2 units out as rovers and one as a base and get +/- 3feet? If so what would be the proceedure?

Thanks Charley

I always wondered if bad data(which I think you might get because of trees & houses) in a PM2 setup, such as you're contemplating could ever be worse than an autonomous location.

If you use a 15-20 foot rod, you might do better with locations, but the time involved with initialization, and the HEADACHES of dealing with 4000 bits of data(post-processing) in A.S., to me seems close to insurmountable, when you consider worrying about such things as losing lock(which, often you don't realize UNTIL you post-process).

I think you'd do better to use the PM2 units to establish control on "useable" points, then returning with a total station to get the data.

What I hear about the MM-CE, it might work, but I don't know how long it actually takes to get a guaranteed location of less than 3 feet.

Do you expect to have a helper, or is this a SOLO operation?

OPen sky ???

With Locus units and WIDE OPEN SKY
the s&g procedures work.

Just remember Trees and GPS don't go in the same sentence.

jimbo

And neither do houses, tall semi-trucks, buildings and walls.

For that matter, telephone poles can be a real problem, as well as power lines.

All I can say, is make absolutely, positively certain that the base(s) have completely, totally open skies. The last thing you want is to have 5 sats on a rover while the base has lost one of those 5, even though it might have a total of 7 or 8.

This project, to me seems very iffy using GPS alone.

I re-read that you want to use 2-rovers(twice the headache I'm afraid). For certain, I would establish a lot of good control and use a T.S.. It would be much faster.
Modified By John Francis on 9/21/2005 at 9:53 AM

Mobile Mapper is a better tool for the semi obstructed environment you describe. Use the PM2's as a local base to keep baseline lengths short and use an external antenna and prism pole to get up over rooflines and shrubby obstructions. $1600 or so spent on the right tool can make you money rather than forcing the wrong tool in there. Plus you get another carrier phase capable unit (did I mispeak :p) to add to your existing PM2 collection.

Finally, if you can live with meter level results then you should consider putting a beacon receiver on your PM2 and using the nav functions. A close USCG beacon source on a PM2 with the external antenna can be a quick way to map averaged waypoints and export the positions. Phil alluded to this capability a few years ago as a science project, but I have not yet tried it myself.....

I have, however, used a Garmin xl12 with an external Skymaster antenna and a beacon source extensively and get 2 meter positions after a few minutes of averaging waypoints. Low cost solution with existing tools I already own. However, if you spend $900 or so to get a beacon receiver from CSI or even the Thales model, why not spend the money for the MM and get more bang for your buck?
Modified By Robert Bills on 9/21/2005 at 11:02 AM

We are just finishing up a survey for our rural water districts and outside water sales. It covers much of one entire county.

This involved mapping several thousand water meters (I'm guessing this is what you are talking about).

There were some important side issues concerning who's meter each was and did they have a valid account. The accounts are tracked based on the serial number stamped on the meter.

Another issue was the size of the meter. We found a few 8" meters that were listed as 2" meters. Big difference on the amount of drawn down on our water system between the two.

So we needed to also gather attribute data.


Meter Brand
Serial Number
Size of Meter
Address if possible (not likely in rural areas).

Your project may not need this information, but you might check with them and see. Sometimes they don't really know all that they will need.

You can make more money doing it all the first time and saving them a second trip.

Just food for thought.

We have been very happy with the Mobile Mapper and about three minutes of data to get reliable near foot x,y,z's. Usually entering the attribute data takes 2 minutes, so not much wasted time involved.

You could place your PM2's in a safe place and use them as base station data for the post processing if you do not have a local CORS.

We have found no degradation of data up to about 40km.

I think the MM or the MMCE is the better tool for this type of project in my humble opinion.

I hope you don't mind the comments since I didn't really address your question.

Deral Paulk, PLS OK

Good advice in the posts above and to be taken into consideration. I would add that you can probably get better and more reliable results by setting up two of the ProMarks as base units and only using one rover. Try it out on a 100 or so shots to verify. The advantage of using two base units is that if both vectors to the rover don't agree, you can be pretty sure that the shot wasn't good. If they do agree, you will end up with impressive results.

The alternative, if you are interested in meter-level accuracy is to run the ProMarks in Navigation Mode and select UTM coordinates for either the Primary or Secondary coordinate system. I did this a year ago to locate soils investigation test pits on a site. When I correlated positions with the property corners, the largest residuals I obtained were a meter or less.

Just a note.

That also works in MM Office.

You can process the MM file with one base station then output the results and then process against the second one and compare.

The only problem is multipath and such which will be common to the rover(in each processing session) will skew both results in the same direction.

But it is a check and one that takes little time.

Deral Paulk, PLS OK

I will be looking at the MM and the MMCE.

This project is in an urban setting. The city is just starting it's GIS and has hired me, full time, to "get it done". I already have most of the MH's and WM done, which I used a Leica 500, on loan from the county.
Problem being one unit, one man many point to collect.

Now the powers to be have ask me to do all of the water services also. Which they told me they did not "think" they need at the beginning of the project, but now decided they had better get them also. I was just trying to come up with a method to obtain the data with a resonable leave of accruacy with less time and more man power.

Thanks again for all the input.
Charley

Since you say it is urban.

Get a Mobile Mapper and post-process all of your data.

Buy a pull behind golf cart from a garage sale.

Rig up a range pole and bracket for the MM and get a fixed height for the MM Antenna.

BTW-The MM is the best tool for gathering fire hydrants also.

Brand
Year of Manufacture
Address
Steamer (yes/no)
FHV (yes/no)

If the town is going GIS then attributes are what make it intelligent. It allows them to be proactive in their programs.They can ask question about the data.

A town of 4000 is pretty small and likely has a limited budget.

You can use the MM for many other projects to populate their GIS. And it only takes one person.

Deral Paulk, PLS OK

If you use a golf-cart with the pole attached, keep in mind that you might well blow your 3' requirement, cause the 3'(if you get it), will be from the cart . . . not the hydrant.