On the way to work today, I passed by a couple of surveyors armed with tripod-mounted scopes, who were checking out the next piece of San Diego open space scheduled for destruction. It ocurred to me that GPS technology could make their jobs obsolete. Why would anyone have to take sightings off mountains or other landmarks, when they could just ask a satellite to tell them exactly where they were?
Don’t remember the specific measurements I’m about to “quote,” but they’ll give you an idea.
Consumer Grade GPS has a resolution of about 100 meters. The satellites can actually change this resolution during time of war (they ARE U.S. owned) to prevent the enemy from using our own GPS against us.
Military/Government/Licensed-Operator-grade GPS only has a resolution of 1 meter (or maybe 10 meters?).
Besides, sometimes when you see a surveyor, they’re not necessarily looking for property lines. They need to check grades and relative elevations for engineering purposes. You know, that way they don’t build a whole building tilting slightly.
I think accuracy is one reason surveyors are still needed. With differential GPS, I believe you can get something like 10 centimeter accuracy. That’s overkill for hikers, great for cruise missiles and auto-landing aircraft, but insufficient for architectural site plotting. Also, I believe differential GPS requires ground-based towers, limiting its wide-spread use. Commercial GPS receivers are even less accurate.
Ah, I figured the accuracy of GPS was a factor. However, the question is will GPS someday be accurate enough to put these surveyors into the bread line?
Survey teams with transit, and chains, and sweat can “close the loop to within a hundredth of a foot.” on such things as building site locations. While it might seem like high tech could do better, the high tech that helps most is replacing the old fashion chain with a laser, and keeping the same set up with transit and pole. You put a mirror on the pole, and the fancy-schmancy new transit gives you both angles, and the distance to the pole. (When you are following a hundred-year-old property line through the woods, I promise you, dragging the ass end of that hundred foot long steel tape along with you can be a real assbreaker.) That way you can get elevation above a known position at the same time, combining two operations with only one crew. GPS doesn’t do that.
Just a point, though on the military target tolerances for GPS, if you use multiple satellites, and successive approximation, without the interference, you can get accuracy to one meter. It still only takes a few minutes. Real time, you can only rely on ten meters, with moving targets, although your confidence within ten meters is very high. (When you have had the time to ascertain the precise location of reference points, you can use other systems to reduce those circles again, in extreme cases to centimeters, such as the systems measuring plate techtonics.)
Tris
“Here Kitty, Kitty, Kitty.” ~ Erwin Schrodinger ~
Surveyers will be the users of the GPS.
If a bank is financing the purchase of some property, they will want a survey. The bank president could use GPS and do it himself, but will probably hire surveyers to do it. If the survey company uses GPS [when it gets accurate enough] it will let them use fewer people and lower survey costs.
I can get 9 feet estimated position error with my Garmin GPS 3, even while in a moving car, if I can see enough satelites. Typical accuracy, though, is around 9 meters.
Somebody still has to know what data is needed and how to get it, put the stakes in the ground, draw the maps, etc. The way a surveyor does his job has changed a lot over the centuries and will continue to do so, but it won’t be eliminated.
Yes, 1-meter accuracy isn’t good enough for settling property lines, or laying out building foundations, or much of anything else on a fine scale.
The dither on GPS was shut off last year after years of complaints from almost anyone who used the system. The commercial version is now as accurate as the military one, and the differential mode is now useless. That simply applied the measurable difference between an accurately-surveyed point on the ground and the position GPS said it was, and applied that difference to all other GPS readings in the vicinity, effectively neutralizing the dither. Oddly, the only other time it was ever shut off was to prevent interference between the aircraft and missiles of different Allied countries during the Gulf War. A system intended to keep enemies from using GPS against us during war was actually used at all times except during a war.
…when I worked as a surveyor for my state’s Natural Resources Commission, we began using Leica GPS equipment to put co-ordinates on existing benchmarks. Using post-processed DGPS we were able to obtain sub-centimeter accuracy in horizontal location, but the vertical result wasn’t useful for engineering. This would have been 1993-94. The technique was to set up on a known point, observe on one to three unknowns for up to a couple hours, and send the data back to the office (using a throbbing 2400 baud modem) for another hour or two of processing (on a 486-66).
I’ve got some pics around somewhere, if anyone’s interested I’ll put them online.
We still ran conventional levels, but were looking at laser leveling, in which a tripod mounted laser reads a kind of bar code on the leveling rod. Cool stuff, but the boss was funny about elevations and didn’t really trust the idea.
I kind of miss surveying sometimes, but then I remember the mud, bugs, ankle deep mud, rain, snow… Then I remember that I work inside now.
-mdf
I checked to see if any of the web page I worked on for the NRC was still there, and found this link:
http://www.nrc.state.ne.us/floodplain/photogram.html
The equipment shown is what I used, I hear there is more compact hardware in use now. Take a look at the Photogrammetry and Digital Photogrammetry links. We were just getting started in digital when I left. There are also some more in-depth links at the bottom of the page.
-mdf
I think the key point to remember is that no matter how sophisticated the technology becomes, someone will have to physically go out to the site and take the measurements (and interpret them). Apart from engineering, surveyors play a vital role in cartography. Accurate measurements of the topography of mountainous regions can be obtained by satellite. However, measurements of the transportation networks and hydrography are best obtained by an onsite observer.