Memorandum

To: Amanda HaruchFrom: Courtney SellDate: 4 October 2015Subject: Project 2- Technical Definition and Description

This memo states the audience, purpose, and placement for the technical definition and description of my chosen term for Project 2. The term I chose is total station. The technical definition and description are found in the pages following this memo.

AudienceThe audience of the technical definition and description are University of Idaho students in an introductory topographical surveying class. It is specifically geared toward those in the Civil Engineering Department who will use it to create topographic maps for planning and designing roadways, buildings, water storage, or other civil engineering projects. It is assumed that they have a basic understanding of the difference between slope and lateral distances in calculations. The audience also has basic knowledge of AutoCAD or Civil3D programs and would know how to import the data collected from the surveys and how to proceed with the data points.

PurposeSome students in the Civil Engineering Department will choose a career path that requires them to use total stations to survey a site and produce data that will assist other engineers in design processes. Having a basic understanding of the equipment and procedures that can apply to most situations is vital so that the surveyor can go to a site and begin surveying without having to refer to an instruction manual or other senior surveyors.

PlacementThe targeted location of the technical definition and description would be found in course material for a surveying class. It could also be published online for students at other universities or colleges who are taking introductory surveying classes.

Technical Definition: What is a Total Station?

A total station is a combination of an electric theodolite and an electronic distance meter (EDM) used in topographic surveys. They are used to measure slope distances from the instrument to a particular point, which is helpful in creating maps or construction layouts.

The total station is a complex machine with many electronic compartments on the inside. The physical pieces that are used in taking the survey data, however, are much less complex. The most useful pieces on the total station are the objective lens, optical sight, horizontal and vertical angle adjustment and lock knobs, plate and tribrach level bubbles, foot screws, digital screen, and keyboard. Two other vital pieces of equipment that are needed for surveying using the total station are the reflector prism and tripod.

1. Objective Lens. The objective lens is like a telescope to spot the reflector prism. This lens has crosshairs through the center of it to align with those crosshairs in the prism to make accurate and consistent readings.

2. Optical Sight. Most total stations have two optical sights; one on the top and bottom of the objective lens. They are small sights with no zoom, so it is like looking through a tiny window (or a peephole with no curvature). Locating the reflective prism by using the optical sight roughly aligns the objective lens with the target so it doesn’t have to be tracked through the objective lens, which can be quite difficult over long distances.

3. Horizontal and Vertical Angle Adjustment and Lock Knobs. The angle adjustment knobs fine tune the alignment of the objective lens so the crosshairs on it and the reflective prism align as perfectly as possible. The smaller lock knobs keep it in to place to avoid any small movements from the wind or touching the total station.

4. Level bubble. Two level bubbles are on every total station. One is located on the plate to measure horizontal levelness. The other is on the base of the total station to find the general levelness of the total station once it is attached to a tripod.

5. Foot Screws. Food screws are used to make fine adjustments in leveling the instrument. Two knobs can be twisted at the same time until the bubble on the total station base is in the center of the level.

6. Digital Screen. The digital screen displays the height and location of the total station as well as the elevation and location of the target.

7. Keyboard. The keyboard is used to navigate the digital screen. Some of the most important buttons on it are the data storage to be able to import into a computer system later and the angle buttons to measure the horizontal, vertical, or slope distance from the total station to the target.

8. Tripod. The tripod is a base for the total station that keeps it level and allows for rotations. 9. Reflector Prism. The prism is a mirror target placed at a given point to be surveyed. It has

crosshairs that identify its center.

8. Tripod

9. Reflective Prism2. Lens

Technical Description: How do Total Stations Work?

Total stations use electronic distance meters to determine distances and angles to certain points. Below describes how the total station calculates these measurements.

The total station is placed on a tripod in a location where there are very few visual obstructions in the way of points that the surveyor wants data on. After it is set up and leveled, it can accurately find the vertical distance, horizontal distance, slope distance, and angle from North (zenith angle). It does all of this by shooting a small laser at a reflective prism that bounces back to the total station.

The laser is shot from the objective lens of the total station toward a reflective prism that is on a specific point. The laser reflects off of the prism face back to the objective lens of the total station. Internally, the total station can calculate the time it took the laser to return and what angle it came back at. When those are combined, it produces various types of distance measurements on the digital display screen. These measurements include horizontal distance, vertical distance, slope distance, and angle of change from the previous point, if there was one. These values are stored in the total station’s internal memory so that it can later be transferred to a computer program.

Because the total station relies on the laser being reflected from the prism, this machine can only be used in fair weather conditions. Taking accurate shots is very difficult in the rain or snow because water droplets can land on the objective lens or prism mirror and obscure the angle returned to the total station. It can also slow the time it takes the laser to return. In addition to affecting the laser, it also becomes difficult to see through the objective lens itself to line up the cross hairs with the prism.

It is also suggested that the points being shot are no further than 1,500 meters, or 4,900 feet. Any distance further than that leads to a significant rise in errors. It is difficult to accurately and precisely line up the cross hairs at this distance. At close range, a small offset only affects the data by a few centimeters, but as the distance increases, these offsets could lead to several inches or even feet of skewed distances.