One Fix Wonders

I feel your pain. I could tell some stories.....

In the "primitive" years of GPS (how's THAT for an oxymoron), before "real time", I processed hours, days, weeks and probably months of static data. Of course this was almost a necessity because sometimes it is hard to get a good constellation geometry with only six SVs. Although taxing and boring, the education was priceless when it came to actually watching what can happen to positional determination within an interdependent network as it unfolded.

As the PLS supervisor I use to race between static stations with batteries and water and checking on each operator and receiver. Once I pulled off the road at a station but was careful not to get the big truck too near (30' or so) the receiver to avoid multipath. As I processed that day's collected files I noticed the data from that particular station got a little squirrelly during the exact time I had the truck near the receiver. We talked about it and altered our procedures. I was amazed at the effect small things had on the data at times.

Post-processing the data gave me some wonderful insight on what it is that is really going on when you are trying to determine a position. And the math can lie to you just as bad as an ex-wife. I've seen stations that can be squeezed to look great on paper, but the adjustment was just smoke and mirrors. I use to tell the guys it was like fermenting wine...it takes a while and you really won't know how good it is until you're finished.

I'm guessing there is a good number of owner/ operators that don't understand the mechanics of static observations but will argue the validity of their "on the fly" vectors ad-nauseam. It's too bad, too. We have this wonderful and complex extra-terrestrial system in place, and some surveyors are reporting distances that would be closer to actual conditions if they 'dropped steel' and flat chained it with a piece of Kiel. I run into it also. And the worst perpetrators are the least likely to listen to anybody.

It is so easy to believe numbers on an LCD that are carried out to three or four places.

Mr cash, I too cut my teeth on static L1 post processed GPS.
It has done the same for me... Given me a good foundation to consider GPS based data today.
Many of the better surveyors who employ GPS, learned about things that go wrong, with static L1.
N

I usually set a couple of even foot offsets in a nearby open area, chain or tape the distance and check the solution. If the offsets are to far to chain, its time to pull out the total station. Any time you are under trees or near a tall building, chances of a bad solution increase exponentially. If you set on a monument for 20 minutes waiting too acquire lock, chances are the solution is wrong.
I too have found corners in the wrong location or an increase of corners supposably set but not recovered in areas with heavy coverage. I know several Surveyors that have GPS but no other equipment to set corners where a GPS solution is not available, so when I don't find a corner under coverage, it doesn't surprise me, but it does bother me that I have to set corners that should have been set by another surveyor. There is a surveyor in town who uses GPS, that I have come to the conclusion that he doesn't know what a fixed solution is. A foot or two is common error in most of his work.

Shouldn't the post title be.. "One Fix Blunders"

RTK has its own little idiosyncrasies in the clear without purposely trying to force a position in tree cover. I would like to think it is ignorance, but am more afraid that it is probably laziness. If in doubt, I always set two points in the clear and then traverse to or set the point with the EDM. I too, am also seeing more distance errors by other surveyors with RTK. Some surveyors might be closer by guessing. If you are a younger and inexperienced surveyor reading this, be assured that you can get multiple wrong positions with RTK that all agree with each other. Many wrong positions that agree with each other will not make it right.

J. Penry, post: 365653, member: 321 wrote: RTK has its own little idiosyncrasies in the clear without purposely trying to force a position in tree cover. I would like to think it is ignorance, but am more afraid that it is probably laziness. If in doubt, I always set two points in the clear and then traverse to or set the point with the EDM...

I get a call at least once a month from another local surveyor concerning my equipment....They've driven by and seen my guys with a TS and they're usually asking if my GPS equipment is in the shop! :pinch:

Our GPS equipment is a wonderful, productive and integral part of our tool box, but total and blind dependence on its solutions only is directly contrary the first couple of chapters in every elementary surveying textbook. Proving your work is just as much a part of our job as performing the work itself. Part of our procedure is redundant verification of at least two of the controlling distances within whatever it is we're doing. It took a while to get my PCs to understand $50K worth of yellow gear can be wrong in various ways. One of my employees, right after being hired, questioned the practice with disbelief; "You're kidding, right?" was his reaction when I told him to get out the gun and shoot a couple of specific points.

I have to admit it took a while, but the same guy got his feathers all up in a fluff when he actually ran into a point with a location that disagreed with the RTK by a few feet. He couldn't figure out what had happened. Truthfully, I could not explain it either, but we had a string of points that were bad. I made my point, "This is why we check, check, check." Thankfully all of my employees have seen actual instances where the old DC has lied to them and they understand the concept of not only location and recordation, but of verification also.

paden cash, post: 365670, member: 20 wrote: when I told him to get out the gun and shoot a couple of specific points.

My old boss would've added: It only takes a minute, pardner...:-)