I was asked by a city Public Works staff person today what sort of GPS hardware and software they'd need in order to be able to go into the field and collect positions on infrastructure items (wells, valves, manholes, etc.) and end up with 1m or better positions. After explaining to him that I have no experience with this level of GPS positioning, I said I'd nose around a bit and give him an idea of his options.

Any of you with GIS experience care to share your knowledge?

Thanks.

for hardware, the Mobile Mapper with the post processing option will most definately fit the need. The Mobile Mapper Office software handles the p/p work as well as the WAAS collected data, when WAAS is "close enough. The post processed positions, using a fairly nearby base (CORS or user L1 base) will give definate sub-meter positions.

It's also really cool, as a boundary surveyor, to put your acad files in either a .shp or .dxf format into the MM (properly georeferenced) and use it for project site navigation in real time.

Actually, this is a question for Deral to answer. It's his game on a daily basis.

jd

What kind of occupation times are required to get submeter with the MM? There's a CORS within 5 miles of just about anywhere these guys will be working, so I assume that can serve as their base.

Jim

What little we've seen so far would indicate that a 3 minute occupation with a CORS in that short range would normally yeild near the foot range for a good portion, and submeter at the 2 sigma level. That is given of course decent sky, 6-7 sv's minimum and pdop below 3.

The CORS can definately serve the needs for a base, but some of ours in NE TX are a bit "unpredictable". We have decided to go ahead and either run a base unit at the office (if within 15-20 miles) or use a L1 unit on site. Actually, the L1 unit on site greatly improves the results so we will most likely make 1-3 miles our standard. Either way, your CORS in the 5 mile or so range will give excellent results, as long as the data is available. We're still a bit ticked about having run a very good experimental session to process to our nearest (and newest) CORS some 33 miles away, only to find the unit had shut down for a 12 hour period..... during our sesion. We were not running our own base station as a backup.

Sounds like the MM would handily meet the city's needs. Any ideas as to the cost of the PP option? (Mike Margolis, are you listening?)

I am here....

The MobileMapper costs $1595 for the real time 2-3meter version and $2195 for the sub-meter post processed version.

Those are handhelds, you can get a dash mount, handlebar mount, magnetic mount antenna or use a PM2 antenna and cable as additional options.

I am told that the Husky bracket works for putting it on a prism pole.

Thanks to both of you. I've passed the information along to my city contact.

Search under Mobile Mapper and look at some of my results taken during our intial testing.

You have to work hard to get good reliable results using WAAS only, and we've figured out a few things to do, such as a 'warm up' and 'letting it settle in'.

The post processing option is worth the money, painless with the CORS and gets much more solid results all of the time. Much our results, using as little as 30 seconds have been in the sub-foot range, and if you look at our elevations, then you'll flip. Much better than ever expected.

The ability to load shape files after you have gathered infrastructure data, or to load base map information is where the Mobile Mapper really stands out.

The Mobile Mapper is very powerful, and the next question would be "What do they have to maintain the base maps and such?" AutoCAD Map, Arcview, other?
What sort of base maps will they be using for the GIS system?

DLG, DRG, DOQQ's, other?

Deral

The GIS Department uses ArcInfo and Arcview, as I recall. The Public Works Department uses AutoCAD Map. They both have .5'-per-pixel digital orthophotos of the whole city at their disposal (as does anyone else who cares to download them -- a very handy resource).

Okay, they got the stuff to work with on the office side.

The Mobile Mapper was our choice based on results, costs, weight and ease of use.

We use the WAAS to find things, but we use the post-processing to add things to our database of infrastructure.

The WAAS is fine to go out and find something already accurate and to just update some attribute information, but we find the post-processing is necessary to get the first position to put into a map.

A typical water line junction will have three valves. Mostly within a pretty small radius. The sub foot puts them where they need to be and you can tell what line they are on.

Sewer is different when the Engineers in Public Works want to use the data in their model. You have to counsel them on the vertical. If they want to really use the data, then they need to use RTK and solid inverts.

In a town with no base maps then the Mobile Mapper is fine to locate things, even SSMH's and SWMH's...to begin their digital foray into the GIS world.

Somethings need more accuracy, depending on their needs. We do our fire hydrants with the Mobile Mapper, but our SSMH's with RTK. The elevation is very important on gravity systems.

Proper tool for each job.

That said, without any maps, then the Mobile Mapper can gather them all for a base map on which they can build.

Sounds like they have the proper software, but you might need to help them with analysis on what sort of data they really need and what they expect it to do.

Public Works in our town means Engineers and they want the most accurate data they can get. They put the results in models and use it to expand our system.

Say what you want about Engineers, but when you actually explain the differences in data quality, they can be an ally when submitting an RFP for work.

Deral
Modified By Deral_ Paulk on 9/30/2004 at 7:33 PM

unfortunately the MM can't handle the digital orthophotos, but the MM CE is on the horizon. First reports were the MM CE would NOT have the post processing capability - a real asset. Actually the earlier "press releases" seemed to indicate the MM CE would be capable of submeter results with WAAS only. I think the latest info I saw (on another web site) had a somewhat revised wording press release that made it a bit clearer on the WAAS only submeter pipe dream.

This week we had to navigate through a recently timbered tract for one of our municipal clients to stake out a site for a proposed sewer treatment plant. We had used every GPS and conventional tool in the tool box to survey the residual tract we had available to work within, including a file I had created in 1989 on some oil well locations on the subject property. Overall it was a heck of a project that gives you a sense of pride in the chosen profession, but way to much details to throw into a MM discussion (better discussed over a six-pack).

Anyhow, the entire tract survey, and the proposed plant site boundary were mapped in CAD, converted to a .dxf file and uploaded to the MM. The actual coordinates for the proposed corners were input as "Way Points" as well. Using the cad drawing in real time allowed us to graphically navigate to the very near vicinity of the corners, and then a "GoTo" got us to within the standard 2-3 meter range of WAAS. This let us quickly set up the necessary traverse from our existing control points to the proposed corners. I doubt seriously we could have done the navigation TO the proposed corners by conventional means as easily.

jd

p.s. Deral....glad you're back

We got our 'toys' today...Bliss...Ah...

Went very well.

Deral

yeah....I saw on the "egg yolk yellow side"....

the high tech bricks


really cool!

jd