Topographic surveys are preliminary surveys used to locate horizontal and vertical points in a defined geographical area. A topographic map is a two-dimensional representation of the three dimensional surface of the earth. These maps are used to represent the shape of the surface. Measurements are taken using differential leveling. The purpose of this lab is to create a topographic survey with measurements gathered in a field south of Taconic Hall on Dutchess Community College. Then using the results create a Topographic map of the field.
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Differential leveling is used to determine differences in elevations between points that are some difference from each other by using a surveyor's level together with a graduated measuring rod. Using equipment properly is essential to accurate differential surveying work. The commonly used Philly rod ("rod " for short), is manufactured from, metal, wood, or fiberglass and has graduations depicted on it in 1/100th of a foot increments. The tripod is a set of three wooden or aluminum legs that are hinged with a platform at the top to affix instruments. There are various height adjustments as well that can be made with the legs and they have metal points on the bottom to insure a secure footing to the various surfaces a surveyor may be working on. .
The Automatic Level (often referred to as the "gun ") is an instrument the surveyor looks through to obtain a reading on the rod. This instrument resembles a small telescope in appearance, and is mounted on the removable tripod platform. There are a set of visible crosshairs within the telescope that the user lines up with the marking on the rod. The optics are mounted on a suspension system to automatically maintain a level line of sight, even if the instrument is slightly tilted. Three leveling screws are along the base that is used to level the instrument along with the on-board circular spirit level.