How do you use a transit to shoot a grade?

Answer 1

Today someone came to my home because of a drainage problem I have. He said, "shoot it to get a grade". It means use a surveyors transit tool to get an accurate level of the ground so that the water can follow better. Ok, everybody that slept through geometry class. A transit is a very sensitive instrument which can be leveled very accurately and can measure angles very precisely, both horizontally and vertically. The surveyor will mark two points on the ground, in the case of a drainage problem probably near the highest and lowest parts of the property. He will then set his transit up directly over one of the points, and will use the levels in the instrument to make sure that the instrument is precisely level. He will then aim the telescope at the second point on the ground and will use the internal scale to read off the "vertical angle" which is the angle above or below horizontal. In an old-fashioned instrument, he will next use a tape measure to measure the distance between the telescope and the point at which he is aiming. In a modern device, a reflector will be placed at the second point, and the transit will measure the distance using a laser device. The surveyor will also measure the distance the center of the transit is above the first point. Using trigonometry, he can then calculate the exact difference in elevation between the two points, and consequently the likelihood that water will drain from the higher to the lower point. If there are further points to be measured, the transit is rotated from one point to another, recording the exact angle turned in each case. Further trigonometry can then be used to calculate the precise location of the remaining points and their relationship in three dimensional space. If the idea is to lay out a pre-determined grade, trigonometry is used to establish the vertical distance necessary to attain the desired grade at the measured distance, and the correct elevation can be marked on a vertical surface. Everyone should take first year engineering.