I like

"OPPOsaurus WRX" (opposaurus) 08/25/2015 at 07:27 • Filed to: None

3

6

Big bolts and I cannot lie

I surveyed a house with water damage. Every plumbing fixture had gold plated handles. Too bad the 4 car garage was empty. I asked the other guy with me if he knew what the client drove. He laughed and said he doesn’t he has a limo

atrombs > OPPOsaurus WRX 08/25/2015 at 07:45

0

Every time I have to go in to DC I wish I had a limo. I hate driving in city traffic.

wkiernan > OPPOsaurus WRX 08/25/2015 at 11:58

1

Are you a land surveyor? I am, here’s my baby, Ingrid.

and 100 more > wkiernan 08/25/2015 at 12:12

0

No RTK for this guy! How old is that unit, it looks almost brand new? I know the industry has changed so much since I did was working with survey.

OPPOsaurus WRX > wkiernan 08/25/2015 at 23:34

0

Nope. Project manager for home damage repair

Rainbow > wkiernan 08/26/2015 at 10:00

0

What exactly do those things do? I remember seeing them all over campus at my previous college, presumably because they had a lot of landscape engineering classes or something like that.

wkiernan > Rainbow 08/26/2015 at 11:17

0

That is a surveyor’s “total station” which combines a theodolite and an EDM or electronic distance meter (not to be confused with “electronic dance music” which has the same abbreviation) in one package.

An electronic distance meter measures distances using an infrared light beam from the instrument to a corner prism, which is a glass target that reflects a beam of light directly back in the direction it came from. A theodolite measures angles in two axes; one is relative to straight up (zenith angle) and the other is parallel with the ground (horizontal angle). While zenith angles are measured relative to the direction of gravity, horizontal angles are measured between three points; what you are measuring is the angle between a line from the instrument and a backsight point and a line from the instrument to a foresight point. You can orient yourself by sighting a backsight and shoot many foresight points from the same setup.

Almost all total stations can not only display the measured angles and distances on the face of the instrument, but also hook up to a hand-held computer (which surveyors call a “data collector”) so that data from shots are automatically stored, without having to write angles and distances down with a pencil in a field book, as we used to do in 1978 when I started doing land surveying. While I’m reminiscing, I’ll also mention that when I started surveying we rarely used EDMs to measure distances; instead we got most distances using 200 foot steel tapes and plumb bobs. Back then I and my field crew measured many distances of up to thousands of feet in places like the center of roads with a steel tape in 200 foot increments, where I could measure the same distance to higher accuracy today in just a few seconds by pressing a button. When we had to measure a distance across a lake we either had to traverse around the lake or locate the far-off point by some scheme of triangulation.

Unlike GPS or astronomical observations, a total station can’t tell you where you are relative to the world, but it can tell, to a very high degree of precision, the geometrical relation between things in the world. So if for example you have a couple of property corners, such as iron rods or concrete monuments, marking the boundary of your property, you can measure other things such as building corners, edges of pavement, other property corners, etc., and see where they lie relative to your property line. And if you have an benchmark with a known elevation relative to sea level, you can measure the elevation of other structures such as floor slabs, pipes, roofs, etc. You can also lay out things for construction with a total station, both horizontally and vertically, e.g. a surveyor can stake out the corners of a proposed building and also set stakes representing the building’s proposed floor slab elevation.

If you’re not acquainted with land surveying you might be surprised at the accuracy of the measurements you can make with a total station; the specifications for that rather old Geodimeter total station you see there are a standard deviation of 5 seconds of arc and three parts per million +/- 0.01 feet, out to a range of at least one mile. If you sight a point 400 feet away through the telescope and turn an angle of 5 seconds, you will be looking about 1/8 of an inch to the side of your point; three parts in a million over a distance of an entire mile amounts to a mere 3/16 of an inch.