L1-L2 GPS difference

There are some L1 units that work RTK. I never used the Promark 2's, so look at the specs. Or perhaps someone on the forum will comment.

OPUS requires L1 and L2, so don't worry about it. You can download the CORS data and run your own solutions. There may be a rinex conversion involved, but it's all do-able.

My first GPS were Magellans. We got them for $900 from an auction at a convention. They worked very well, but it was a minimum of 45 minutes over a point (best conditions) and you could not tell when you had enough data for the solution. There were times we had to return to the scene and locate for a bit longer. Of course, we did try to push the envelope in the other direction and we did obtain reasonable solutions in under 1/2 hour, but it was better to just let the things cook.

Run your surveys in a loop. If you have a CORS nearby and 2 promarks, you can create immediate loop solutions. If the CORS is far away, run some real loops.

The best we hit with the magellans was a 5 point loop (I was subbed to another firm who needed some GPS work), horizontally we missed by 0.01' and vertically by 0.06'. This was tied into a 3-mile open route traverse and allowed the surveyor to run a solution without running another few miles.

There are uses and if you just want to jump in to GPS, grab them. Better to get your feet wet than to dive in to a very deep pool.

Thanx Spledeus,

I guess I am missing something. How do you do a loop with GPS? Don't you just get the position at each observation point - and inverse between them? Where does the "loop" come in? Or are you talking about looping with conventional terrestrial total station and "checking" against a leg or two that you have also GPS?

I really don't understand exactly how I am going to use these guys, but it looks like I probably get them.

Any help would be appreciated to EDUCATE me.

thanx,
geezer:-P

> Any help would be appreciated to EDUCATE me.

A good place to start is the Ashtech FTP site. Download the PM2 STAT TNG-SYS series of PDFs and read through them. They'll give you an idea of how to use the receivers in the field, plus downloading. Then go get GNSS Solutions; install it and go through the help file to see how to process data. That should give you plenty to do before you even lay hands on your new (used) receivers.

I used PM2's for about 7 years before getting Topcon hipers...

No you can not do RTK with them but the static works just fine, in ideal conditions you can get to under 1 cm in about 25 minutes but you need to have the mission planning software to tell you what time of day you have the most sats as you only are receiving gps (no glonass)...anything under 6 sats and you might or might not get a good solution.

You can also do "shot" with them called stop and go, as long as you are in the open it works great, about 15 second shots and your good, but step under a tree and the solution goes out the window.

And its is "post processed" meaning you will never know if you got a good solution untill you download and process the raw data...good to have a laptop with you and do it on site then you know before getting back to the office and finding out things didnt work.

Key thing is canopy, like most gps, it pretty much sucks in the woods unless you can get the antenna above the trees...with our Hiper setup we got a 15' pole that you can get up high but its kind of wobbly and that will cut you accuracy down some but it would depend on what you want to locate I guess.

Spend some money on a good GPS training course before you waste your money on GPS receivers. They are completely useless without good training. You might find that the L1 only units are not what you even need.

I have a Promark2 and 4 Locus units. You won't be able to use OPUS because that program requires L@. Before OPUS, I downloaded files from CORS, it's like having a free unit sitting in a constant position. However, you have to be close to a CORS site (My Promark2 has a limit of 15 km.), otherwise you won't get the precision you need. You will need computer software to process the data files you collect. What you get from processing is a vector (direction & distance), the raw position (lat-long) from the unit is approximate, depending on how long the unit sits there. If you have two units you will need three sessions to get three vectors for a triangle. That's your loop which you can check for closure and adjust. I use StarNet Pro which lets me adjust GPS vectors with my total station data.

So you will need processing software with the Promark2 units.

You only need to tie into a CORS point when you want to be on that coordinate system.

Evelyn

It might a useful tool to learn ancient techniques. I don't see how something like this can make you more efficient or competitive. Think about buying a transit to learn how to wind angles when everybody else is using a total station.

Ralph

You can do RTK with L1 receivers. Single frequency receivers should not be used for long baselines as the Ionosphere delay cannot be calibrated (and removed to first order). L1 receivers are typically fine for short baselines (under 10km)
Here is a good write-up:

http://www.ngs.noaa.gov/PUBS_LIB/NGSRealTimeUserGuidelines.v2.1.pdf

Neil

A lot depends on WHERE you are at (GPS Friendly or not), and the type of work that you normally do. Of course if you want (or need) to align yourself with the NSRS, then CORS coverage and proximity is a factor as well.

You can do some REALLY tight work with L1[only] gear, but a Solar Maximum is NOT the best time for ANY GPS, and especially for L1[only] gear. I bought my L1[only] gear towards the end of the early 90s Maximum, and by the beginning of the y2k maximum, I had L1/L2 gear (even though I still use the L1[only] gear to this day).

I have had EXCELLENT results with L1[only] Networks over the years (including one that covered 75+ square miles), and would still be very comfortable with well designed L1[only] “leap-frog” traverses (assuming that they “closed” well).

As stated above, training is the key! It doesn't have to be formal (pay for it) training, but you will probably need someone to get you started on the right track, and whom you can call with questions as they materialize (and they WILL). You will certianly have do a lot of READING.

It does open new doors, but it's also a whole new ballgame with some different rules to be considered.

Loyal

Mr. Jim: I am wondering about post process software.. you said " go get GNSS solutions.." I am interested, but how much $$? Post process software used to be packaged with the GPS units, but if you buy used GPS, what other software is available for a reasonable price?

Take the basic setup for GPS, one receiver is on a known point (1) and the other is on an unknown point (2). Record for the time you find works best and pick up the unit on (1) and put it on another point (3). Now (2) is the known and (3) is the unknown. After the time necessary, pick up the unit on (2) and put it on (1). Essentially (3) is the known and (1) is the unknown, but (1) is known, so you have a triangle or loop.
It's easier to imagine it like a level loop instead of a closed traverse even though you are now into 3-d solutions. Of course, you can expand the imagination into a triangulation network.

My town is reasonably squarish. When we first got out Hipers (L1 and L2, GPS and Glonass, RTK and Static) I decided to setup a network. I started from a published NGS control point in the east, set a nail in the south, established a drill hole in the west and used an old GPS disc in the north. I let the things cook for about 2 hours per leg. I then went to the middle of town where we have an airport, set on the published NGS point there and radially located each of the four control points. It was a great exercise the learn the equipment and to create the control that we use to this day (with the exception of the GPS disc, a snowplow took it out).

Good luck, Thadd

The L1 Promark 2 units are good for establishing control. As others have said, they have their limitations, but when used properly, are very handy.

I have two L1/L2 Hiper units, and two Promark 3 units, and I can run tight control using post processing techniques. Pay close attention to what the surveyors here say, they know their stuff. As Jim Frame pointed out, the Ashtech FTP site has a wealth of information.

The GNSS Solutions is a free download for the L1 post processing option. Once you learn to use it, it is a very powerful program. There are some good training movies thers under the GNSS Studios folder. I downloaded them, and still refer to them.

Good luck, I think you will like them.

I have 2 Locus and 3 Stratus (All L1 only) Also RTK setup.
I'd try and get a third L1 (preferably all same brand)as that way you have 3 points running simulatenouesly.
I leave one fixed and rotate the others about depending on how much time available.
Generally they sit around all day on same point and I can only attest to their benefits.

I check direct lines with RTK and also total station observations. All up I reckon they are excellent value.

Even with RTK I still find benefit from the L1's.

Check what software is available and what operating systems they works with.

Hope that helps.

> It might a useful tool to learn ancient techniques. I don't see how something like this can make you more efficient or competitive. Think about buying a transit to learn how to wind angles when everybody else is using a total station.
>
> Ralph

I couldn't imagine using L1 in the canyons of NYC but out in the country they work fine. I use Post Processed Kinematic all the time with three L1 units (Trimble 4600's). I also have a Trimble robotic TS but the L1 units are more productive for rural work.

> > It might a useful tool to learn ancient techniques. I don't see how something like this can make you more efficient or competitive. Think about buying a transit to learn how to wind angles when everybody else is using a total station.
> >
> > Ralph
>
> I couldn't imagine using L1 in the canyons of NYC but out in the country they work fine. I use Post Processed Kinematic all the time with three L1 units (Trimble 4600's). I also have a Trimble robotic TS but the L1 units are more productive for rural work.

I can't imagine it being anywhere as productive as a Rover on an RTN network.
I guess it depends. I believe he said he was working solo,

I am an "Old Duffer", solo operator. I have an lead on a couple of Promark 2 units.

I think he should just spend a little more and get a GNSS rover. Much less of a learning curve and he will be productive right out of the box.
I think I saw a system by Champion with a Microsurvey data collection package for under 10k.

If he can get L1s cheap and wants to experiment, that's his call.

Ralph

Hello

I have Sokkia RTK plus static capable GSR 1700 CSX L1 navstar and gloanass (SPL)

it has been... flawless lite simple perfect.

using this system for 2 years now THERE is Jack Zhit for L2

UNLESS you are going plus 3km RTK or 100 km static = some sales man snows you on L1/L2

next on opus or here in Canada versions (PPP) there are LONG range advantages to L1/L2
but i have ZERO use for L2 rtk in the last two years of RTK and some L1 80 km static (good luck on radios).

and i sbsolutely refuse to pack around a L1/l2 RTK boat anchor from trimble or topcon.

PK

Here is a Leica paper on single vs dual-frequency receivers:
http://www.leica-geosystems.com/downloads123/zz/general/general/tech_paper/Brown_etal_L1Monitoring_en.pdf