PROMARK 3

I have three units and have been very pleased with their performance.

Everything has their limits of use. Mine have proved there are some situations that do not work well.

Each unit must have the same settings.
Mine work best 3 to 5 miles from a control point.
Double redundancy (a unit on two control points at the same time) improves confidence around my area.
Good geometry helps immensely. That is for the locations on the ground and in the sky.
A minimum of the same 5 satellites is a must. The more the merrier.
The range you acquire needs to be at least as far as you are from the control point for assured sub centimeter accuracy.

What area you are from will make a difference a to what settings are, especially calculating the scale factor.

Mine have worked very well too. I mostly use them in static mode, 15 minutes minimum. I extend times to double the mileage on the meter especially in situations where there are obstructions.

I AM NOT SAYING MINE WORK GOOD. WHAT I AM SAYING IS I HAD A PROBLEM WITH MINE READING DISTANCE, A SURVEYOR DID A SURVEY BEHIND ME AND FOUND THAT MY DISTANCE WAS OFF BY 10 FEET, NOW I DON'T KNOW WHETHER TO TRUST THEM OR NOT. I ALSO USE STATIC.

I haven't had accuracy problems to that degree. Usually my total station shots match the ProMark 3s extremely well.

I do closed networks with redundancy, though, so that I can detect those sorts of issues. GPS is not a free pass from using a closed, redundant network.

Sometimes even with good intentions, things out of our control happen. Go back and look at that site, do over you occupation and compare that site's information with your other occupations on that project. Check the times against a readout of the constellation of each events. The point data will show the level of good/bad data and if there was any interference.

I follow a guy that uses PM3s and often find him 10-20ft off my findings. Even when checked with a TS.

His procedures are not always that reliable and then sometimes he uses the units with expectations that are beyond their and any other brand capabilities.

I look at it this way, at 95% probability of correctness, there is as much as 5% probability that it is wrong.

Even single and double redundancy can fail or offer incorrect location when the constellation is a mess and not in good geometry and when your horizon is limited. Pine and cedar are the worst problem for me.

I received a cell call during a check of a unit on a point and I believe that messed that location.

Multiple occupations of morning, afternoon and on different days will improve results.

In my area there are many places GPS is not capable of producing reliable results and a close monitoring of the readings must be made to decide whether to TS or take other approach for desirable results.

I have two PM3 units, and have never had any issues at all with them.

I have had good results doing static post processed solutions.

Sometimes I get a floating solution but that is typically caused by having a limited horizon due to the tall timber surrounding a site.

But if the solution is fixed, I can count on it being good data. I generally use my PM3's in a manner which provides a closure, either with a conventional TS traverse, or by multiple observations from alternating control.

Never seen a problem with a position that was a fixed solution.

I WOULD LIKE TO THANK ALL OF YOU FOR YOUR INFO.

If You Reoccupy A Point

and have one of the antenna heights wrong it can throw off other points horizonatlly. It tilts your survey in order to get the best least squares fit. Learned that the hard way. Took a lot of searching and headscratching to find my error.

Paul in PA

If You Reoccupy A Point

Another thing, is that SOME folks think that using GPS results in the SAME coordinate, for EVERY autonomous observation. NOT SO.

I have fought with several surveyors, who did not know that interconnectivity was not needed.

They were not using them correctly.

N

I DON'T THINK THEY ARE DISCONTINUED, IT IS THE PROMARK 2'S THAT ARE DISCONTINUED.