We are running a three reciever static system. My question is this: Is it better to always leave one reciever on a known control point while "leapfrogging" the other two, or once I have a couple of vectors on my known point, is it OK to "leapfrog" with all three (assuming I always have one point from a previous session occupied on all sessions)???? Any help from some of you experienced guys would be appreciated. Thanks, Bob

Bob,

Grab your ProMark2 users guide and read chapter 3 more than once. There are some great diagrams on pages 26 through 31 that will really help you figure out what to do in the field.

The short answer is that you will have a better network if you move all three of those units around and not just leave one on a single control point.

Measure the short lines! I know there are people who will tell you how much that will mess up your accuracy ratios but measuring the short lines is a big deal to your total station work that will follow the static survey.

Just for example, look at figure 3.5 on page 28 in your book. If that were my survey I would measure the vectors between those pairs of points and include them in my adjustment. Ask the guys who have followed my control surveys - the procedures work well.

There are resources on the Ashtech ftp server that will help you on the road to good GPS work. Take advantage of the manuals and things you can download. Mark won't mind if you take computer files home even if he would mind you walking off with the manuals.

Good luck with your new adventure.

One other thought is that you can always close out points to other knowns creating series of loops (which maybe discussed in the ProMark2 manual), which would negate the need for constant redundancy on every point. For example you could run from points 1-10, points 1 and 10 being known, and provided that each point is in a loop connecting 1 and 10 and the closure checks then all points between should be good.

Shawn

My preference is to leap frog. The one thing you have to watch out for it that you DON’T end up with a “pivot point” that is not in the best of locations. If you rely on this to carry your accuracy around and the baselines fail from this point you end up with a problem.

Randy makes a very good point. It is always best if you have more than one route, or series of connected vectors, to compute coordinates for the other points in your project. That way if you have set a point in a location that is just not suitable for GPS you can just leave it out and not have to go do a bunch of field work over again.

I hesitate to use the term "leap frog" because I often moved all of the receivers "forward" through a project. So my "pivot point" did not have the same receiver on it from one session to the next.

An additional comment...

With a 3-receiver configuration, you better leave atleast one receiver stationary. If you move all three receivers to NEW points, you will loose your Network connections. You will isolate your network, this will generate an error message when you try to Adjust the Network.

With a 3-receiver your choices are quite simple:
Move 2 receivers between sessions = more productivity.
Move 1 receiver between sessions = less productivity/more redundacy.

This process of leap-frogging receivers can be co-mingled during the Survey as often as needed. Move 1 Receiver between session A&B, the next session move 2 receivers etc., and so on...

Almost without fail, when setting site control for our projects, I use the following procedures with 3 units.

1. Leave one unit on the #1 project control point.
2. Set first pair of points at one extreme of the project.
3. Set second pair of points at other extreme of project.
4. Leave one receiver on "extreme point #2 and rove other receiver to an interior point #1.
5. Leave receiver on interior point #1 and move receiver from extreme point #2 to interior point 2.
6. repeat step 5 til extreme point #1 is reached
7. conclude with session having receivers at extreme point 1 and extreme point 2.

Leaving a base receiver on control point, and using this method of "leap frogging" not only a good deal of redundancy is achieved, but also a closed network.

Works for me.

J.D. Billings, TX RPLS

We almost always set two and leave them, while moving the third to other points. This gives you two independent baselines to each point (this redundancy will aid in your troubleshooting of vector solutions and in the least squares will give you reliable statistics)..
Usually we then move the two (static) receivers to two other points and again keep moving the third to control points as we expand the network..
We never process between the two (static) receivers,(usually we already have vectors from previous surveys) but this is a Trimble suggested way to insure all of the baselines are non-trivial..
Phil can elaborate on Ashtech, which from his talks, can do all three baselines....
In the Trimble software, when you process all three lines you get a perfect closure, which is not correct in my opinion...
PS- Excuse the logon name...but hey, it's all GPS isn't it...

T'Man

I wouldn't care if you logged in as "Garbage Man", you still got alot of experience to add.(even if you do have yellow stuff)

J.D.

Straight from Phil's well rounded dictionary of terms....He says the Trimbles are Yellow, but cost alot of Green....
We are getting ready to go RTK and you can bet the Ashtech will be seriously looked at...Phil can pass the word, but this board has alot to do with our decision to include Ashtech in the RFP... Plus the Ashtech website has alot of good information (for all GPS users)...
Biggest Plus- I can keep in contact with my ol' buddy.

First I want to thank Deral for the flower. One of the things that time has taught us is that we can do good work with the tools regardless of the color of the box. We have demonstrated that in Oklahoma and Texas, America by surveyors who were willing to compare notes and kick tires and talk to each other. You get to see some of that good kind of attitude right here on the rpls boards. Mark Deal's big dream lives on.

One of the things I forgot to mention to Bob was that the same kind of good information that is in the ProMark2 users guide is also available on the Ashtech ftp server in the form of Practical GPS Surveying.pdf That file is a freebie from Ashtech that even those yellow box guys can use to help them make better static surveys. The same kind of information will help provide better ideas for the control needed for better localizations / calibrations for RTK work.

Trimbo, with God's grace I will be here to answer your questions about those new Ashtech tools you are going to get for as long as you are willing to use them. I have some things left to learn about the new stuff. The tools that Randy and I bought some years ago are so dependable that we did not feel the need to replace them with something new. I told Randy he could be running a faster pace with more modern receivers but he tells me that his pace suits him just fine. When I told him how much less the whole package weighs I may have got his attention. I think he is going to kick tires on new tools just to see what they are like.

I want to make sure that I am not misunderstood about moving everybody forward through a survey. If you look at the network diagrams in the user's guide or in Practical GPS Surveying you will see what lines need to be measured to get a good network. My advice is, when you measure those lines, what receivers are used to measure those lines or what order those lines are measured in does not matter nearly as much as getting them all measured.

When Sharon and I would work on a corridor survey we would "chase" each other through the project. Instead of "leapfrogging" with one of us standing there with our thumbs twiddling we would both move forward so that the lead receiver stayed in the lead and the tail receiver stayed in the tail. If she was in the lead I would occupy the last point she set on with my receiver. Balance your approach to a GPS network in a way that will get the measurements you need in the most cost effective way. Sometimes that means making all the measurements on one side of a river (or interstate highway), then making all the connections across the river, then making the remainder of the network connections with everybody on the other side of the river. GPS surveying is about the amount of time spent between sessions as well as about the amount of time spent on a session.

Try to measure lines that will connect together with each day's work so you can process every day with a connection between your vectors. I suggest that just as a housekeeping method. I really don't know why the software would even care what day each line was measured as long as you ended up with those network connections.

With five dual frequency receivers in the field I would try to make sure that in one session we would get all of the really long lines that we need to measure done. Then we might move over so that we would pick up all the not so long lines. Then everybody moves onto the project site to start knocking out those short lines.

You can see some of the method to my madness if you download the RINEX files for the OSU-OKC project from the web page at http://www.osls.org Be forewarned. There are some sessions in that download that are duds! With many survey projects you get the good, the bad, and the very, very ugly. Since we were doing that project to provide educational tools for survey students it made sense to provide them with a can of worms as well as some reall