how do surveyors take measurements of large objects?

Question

or construction engineers

Answer 1

Typically using a phenomenum called paralax - It is basically trigonometry... There are many devices which use these concepts. But the basics is simple trig. You just need to measure a few distances and angles and you can figure out the rest.

Answer 2

It all boils down to angle turned and distance for horizontal measurments (plan view). You have to start from TWO known points. You occupy one point and backsight the other. Then you turn an angle and measure the distance to an unknown point. With the angle and distance, you can now caculate the new coordinate. Then you move to the new point and backsight the one you previously occupied. This is called traversing and these points are called control points.

If you want to get additional data, you get some side shots from your set up. Again, you measure angle turned and distance.

Most equipment now days will also get vertical elevations with pretty good accuracy if the shots aren't too long or the air temp. too hot.

If your elevations have to be very accurate, you have to run a level loop using an instrument that is just for leveling. You measure the elevation differences between to points in one direction and then do it going back and see if you close to within the allowable closure, say 1:10,000.

Answer 3

the kind of measurments depend on the required data , for example: in many projects , engineers are more concerned about horizontal control (horizontal angles , distances and co-ordinates) , and in other cases , they are more concerned about vertical control . anyway .
in a simple surveying project , the building or any thing is divided into polygons(triangle , square ..) and in this case , the surveyor ocupies a point of known co-ordinates called(control point) with an angle measuring device as theodolite or total station and distance measuring instrument as a simple tap or EDM . by knowing the distances from control point to the edges of the divided polygon, and the azimuthal angles(horizontal angles measured from north direction) . he can calculate the co-ordinates of the edges . same in case if circular parts (by knowing the centre and radius)
in case of topographic (vertical) survey it is done by a level instrument and a staff (4m long vertical ruler) the surveyor occupies point of known elevation and the staff is placed vertically at the required point and the level creates an imaginary horizontal surface which intersects with the staff in a point and by knowing the level height the elevation of the required point can be calculated .
today there are more simple methods like GPS which can perform horizontal and topographic survey but not very accurate. that's all !!!