Guys, what have you been experiencing with the PM3s as far as Stop & Go and Kinematic? I am trying to make them get down to a couple of cm for accuracy but am consistently getting more than 50 cm error. I am recording at a 2 second interval on my base and on the roving unit. The rover is initialized on the init-bar (5 minutes), I occupy each point for 15-30 seconds and still get an error as mentioned (PDOP from 1.6 to 2.3, 7 to 9 sattelites). Does anyone have some pointers for me? Thanks

P.S.: Well, it seems that the init-bar is not that great for accuracy. Doing the same and actually initializing to my second known point improved the accuracy to 2-4 cm. Still, if you have any hints, let me know...
Modified By Lukas Duruttya on 3/7/2006 at 10:45 AM

I haven't used the PM3 for S & G(except for screwing around once).

So . . . in a way, I hope you're either doing something wrong or have a "bad" unit.

My guess is you have a procedure problem using the init bar. As you can see, an init on a known point works pretty well. This is the way we do S&G. There isn't anything wrong with the bar, but you must follow the proper procedure. Reread the manual and work slowly through the process again.
Or you can do like us and forget the bar and use known point inits. This will get you to the accuracy you are looking for rather easily.

It'svery odd that the errors on't remain consistent when you DON'T use the bar.

Are the errors always the SAME DIRECTION off and can that direction be roughly the direction from your Base to the direction of the actual bar?

Test your theory by using the init bar first, then going to your "known" point and then doing your job...Then go back to the init bar as your last shot of the session and take a new point. Compare the init bar position to the last shot you just took.

Another way of saying the same thing is to just to do a two point job...Run the init bar first then set a s&g nail. Then go back and take another shot on the init bar...Now start another session and do a known point (staying on the nail for your first session) and then hit the init bar as your first sideshot.

As S. says, it's got to be in your procedures somewhere...so debug them and then if it still happens hit this board again.

Throw the int bar away....
I remember being told that early on by somebody...THe bar can move...set a nail or other substantial point....

I'm not sure that init bars belong in landfills. While it's true that the init bar may rotate, I think that after you have placed the antennae on it and it comes to rest, it will still provide a valid initialization, even if it is in a different position than it was for any previous initializations. I think the solution to resolving the integer ambiguities using the initialization bar only needs the distance between the antennae, not the bearing, and the bar provides the known distance that is required. However, I stand (sit, really), ready to be corrected on this point. Your point regarding setting a nail is acknowledged, though. Fumbling around the near the base trying to put the antennae on the init bar can be fraught with the hazard of disturbing the base receiver. I've always only used the bar for my intial initialization and have always had good results using the recommended 5 minutes.

Bill Wingstedt

The "known" is that the bar is 20cm in length. The "unknown" is the direction of the bar in relation to the base receiver.
If you use the bar for an initialization, that particular setup will have it's own unique 4 character site ID for the initialization point i.e. "where" on the circle of a 20cm radius the rover happens to be. If you break down the base setup and then come back later to the same point the base was on and use the bar to once again initialize a rover, you'd better use a new unique site ID for that initialization point.

Dangerous Dave
Modified By Dave Huff on 3/9/2006 at 5:53 PM

The dangerous one has spoken. So let it be written, so let it be done.


(in case you couldn't tell, he's right).

Use a NON rotating tribrach adapter for the int-bar, I learned the hard way early on.

are you guys saying that your initialization bar moves during the init session?

Or, are you saying it moves while removing the antenna for a S&G session.

If you're worried about the former, you shouldn't be trying to work in such strong wind anyway. If the latter is the case, then the simple solution (and I think it was mentioned in early instructions of performing stop and go kinematic work) is to move to the pole and immediately occupy a nail for a return control point, then set control nail periodically along the way as you work. I wouldn't return to the bar for a re-init anyway.

J.D.
What I learned was the first few times during the initialization, in order to make the cable reach, I leaned the top of the rover rod (minus its antenna) against the I bar causing the I bar to slowly (but not always)move during the int. which gave me an error message, loss of lock if I remember, its been a while. Thot I would fess up and maybe help someone else that was doing the same. Now I just set the rover rod up a couple feet away that will allow the antenna cable to reach.

Duane

We really don't use the bar for ini anyway. We set a nail 10 feet or so from the base unit and start the S&G session with a 10 minute initialization session on the nail.

We've used Locus units as base units, ProMark 2 units as base units and Topcon Hiper units as base units. All with success.

Setting nails along the way is good insurance to have a control to check in to.

jd