How do you compare and contrast the accuracy and reliability of different land surveying instruments?

1 Chain and tape

One of the oldest and simplest surveying methods is using a chain or a tape to measure distances along a straight line. A chain is a series of metal links of equal length, while a tape is a flexible strip of fabric or metal with markings. The chain or tape is stretched between two points, and the number of links or markings is counted to determine the distance. This method is easy to use and inexpensive, but it has several limitations, such as errors due to sagging, stretching, or bending of the chain or tape, or obstacles along the line.

2 Compass and angle

Another common surveying method is using a compass and an angle to measure directions and angles between points. A compass is a device that shows the magnetic north direction, while an angle is a device that measures the angle between two lines. The compass and angle are mounted on a tripod and aligned with the points to be measured. The compass reading and the angle reading are recorded and used to calculate the coordinates of the points. This method is faster and more accurate than the chain and tape method, but it still has some sources of error, such as magnetic declination, local attraction, or instrument errors.

3 Theodolite and transit

A more advanced surveying method is using a theodolite or a transit to measure horizontal and vertical angles between points. A theodolite is a device that has a telescope mounted on a horizontal and a vertical circle, while a transit is a device that has a telescope mounted on a horizontal circle and a vertical plate. The theodolite or transit is set up on a tripod and leveled, and then the telescope is aimed at the points to be measured. The horizontal and vertical angles are read from the circles or the plate and used to calculate the coordinates of the points. This method is more precise and versatile than the compass and angle method, but it requires more skill and time to operate.

4 Level and rod

Another important surveying method is using a level and a rod to measure elevations or differences in height between points. A level is a device that has a telescope with a crosshair that is parallel to the horizon, while a rod is a long pole with markings that indicate the height. The level is set up on a tripod and leveled, and then the telescope is aimed at the rod that is held by an assistant at the point to be measured. The height of the crosshair above or below the rod marking is recorded and used to calculate the elevation of the point. This method is simple and accurate, but it requires a clear line of sight between the level and the rod.

5 Satellite and GPS

The most modern surveying method is using satellites and GPS (Global Positioning System) to measure distances, directions, angles, and elevations between points. GPS is a system that uses a network of satellites that orbit the earth and transmit signals to receivers on the ground. The receivers can determine their position by calculating the time and distance of the signals from different satellites. GPS receivers can be handheld, mounted on vehicles, or attached to surveying instruments. This method is fast, convenient, and accurate, but it depends on the availability and quality of the satellite signals, which can be affected by weather, interference, or obstructions.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?