GPS
Guess
Positioning
System
Back about 15 to 20 yrs ago, my mentor in RTK gps let me tag along. To see what it could do.?ÿ
We were in woods. We surveyed about 80 acres that day. Set 6 or 7 corners.?ÿ
he??d set the gps up, gain fix, then store it. Then inverse to the corner to be set. Compass and box tape came out, and 2 minutes later we were done. No check shot. Nothing else. That was it.?ÿ
foreward a few years, and I??d bought my own. Topcon Legacy E. I went to a nearby section corner, under an oak. Set up on it for half a day. I got a pile of coords, mostly within 3 foot circle. Some 5 or 7 ft away. I developed a little pile all within a radius of .3??. I quit. I guess I got it within 1/2 a foot. But probably within a foot for sure.?ÿ
It was just a test. I did not need it for my survey. I came away with a basic knowledge that, there is a relationship between the ??harder it is to get a shot, the more prone it is to error?.?ÿ
Since then, I??ve found many minor gps mistakes. In the range of 0.3??.?ÿ
a few mistakes in the range of 5-8 feet.?ÿ
Recently, I??ve tied several points set by GPS mentor above. 6-8?? errors. Very challenging places.?ÿ
So, when retracing surveyors, who bought into GPS gospel truth, and did not check themselves adequately, your search area can be a 10?? radius.?ÿ
I also found another that was 8?? from where a surveyor set it. I??d tied a number of his points, and was confident that I was ??into his system?. But, that one under the pines was out by 8 feet.?ÿ
No rhyme nor reason.?ÿ
Just another GPS delusion.?ÿ
Please remember. If the landowners don??t destroy the monuments, and it??s a challenging GPS point, it??s statistical probability of being off a few feet goes up by a magnitude of 5 or 10.?ÿ
O well.?ÿ
If you don??t verify and be sure, you will usually get found out. This includes me.
Rant over. For now.?ÿ
Nate
The two most common problems I've uncovered are bad inits (probably what you encountered) and incorrect or inconsistent datum. Occasionally the US Survey versus International foot shows up. They all share a common fault. Many fail to learn what constitutes a check, while others don't see the need. This is not limited to GPS. A lazy or ignorant person will act the same regardless of the tool of the day. A conscientious practitioner will put in the work every time.
Magic boxes tend to frighten me.?ÿ It could be anything from a simple ohm meter to GPS and LIDAR.?ÿ Calculators and computers hiccup from time to time.?ÿ Anything involving an electrical power source can be wrong.
8' is still better than the search area for chained monument in rough and remote terrain, or the 1960's?ÿ helicopter EDM surveys in Alaska.?ÿ?ÿ
It's shocking what I don't know about electricity.
Grin!!!
Something that is a major pain (literally) around dairy farms is a little thing known as stray voltage.?ÿ It can tickle, it can tingle, it can knock you or the dairy cow dancing the four step on one's butt.
Can't afford the distribution losses of DC over practical distances because you can't use transformers to raise the voltage on the distribution lines and lower it at the user.?ÿ Edison was going to build a dynamo house ever few blocks, and Westinghouse didn't need that for AC.
AC & DC are very different for sure. But what's the definition of a "practical distance"??ÿ Local and centralized power generation might not have been a bad thing.
I like to run "what if" scenarios through my mind like if we were starting from scratch with electrical distribution.?ÿ I'm thinking the world would probably have adjusted and adapted.?ÿ Maybe aerial DC power lines wouldn't collect as much ice in the winter.?ÿ Who knows?
RTK marked a huge improvement in the accuracy of property surveys and a degrading of construction surveys, particularly elevation control.?ÿ
Of course, I live in the plains, not too many trees and since there is very little mountain work available most multipath is easy to deal with. Living in the eastern jungle would probably have made early RTK mostly useless.
But I retrace RTK surveys often, it's rare to see a "bad" monument. As far as coordinates, I exclusively work in B&D when locating monuments, coordinates are what I make them as function of record measurements.?ÿ
as we have come this far off topic...
Easiest power company I ever worked with for plans, asbuilts, etc was a tiny hold-out sitting in the middle of a PUD. My buddy then bought a house where the same thing exists (different one).
Main difference with the big PUD: lower costs and better service...Maybe Westinghouse had a point!
Localized power generation=resilience. Ask Texas.
I've only come across one subdivision that was done with RTK that was totally Fubar. Fairly remote and done by an out of town surveyor, I had to retrace a good part of it for a project and as best I can tell when they scaled to ground, they went the other way, twice. It was horrible GPS country and why they relied exclusively on RTK without any checks is beyond me. When I called them about it, the project's surveyor got really defensive. I figured I had duty to at least call it to their attention, but can't say I made any new friends out it. Fairly recent survey at that, but just one big gobbed up mess.?ÿ
Just because I'm paranoid, doesn't mean they aren't out to get me.
I had a recent ROS to do that needed to be tied into an environmental survey. I don't know who did the environmental survey but it was 7-8' off east-west.?ÿ
I was scratching my head why there was this shift.?ÿ
As I put it all together, I noticed that I was 7-8' shifted from the newest google mapping.?ÿ
I could put in fence corner shots and they all landed about that far from my field location.?ÿ
If you use older photos it would snap back to my coordinates, I can't be sure but somehow I think their coordinates matched the new Google photos. As wild as it seems they may have used those photos as control.?ÿ
It was a big deal cause I had limits to keep from my tract lines and the no-go zones produced by the environmental company.?ÿ
There is a banker. He hires the cheapest survey possible.?ÿ
There is a goof up in his work of the 7 to 10 foot variety. It appears that:
Maybe he set is base up multiple times, but not in the same place.?ÿ
Maybe he got his base nail moved.?ÿ
Maybe he used opus, but somehow never figured out what that does.?ÿ
It??s speculative. But, much of the last 20 years of gps abuse has yet to be discovered.?ÿ
N