How to calculate results on a land survey rod?

Answer 1

The question is a bit confusing in the way it is asked. Typically you use the rod to gain elevation (numbers) and then calculate the elevation of a certain geographical point using a basic survey technique known as leveling. Leveling combines the calculations of a known elevation, known as a bench mark (BM), to the height of a survey level (height of instrument). The process of leveling is done in what is called loops. There are two loops in the process an open loop, and a closing loop. To open the loop, the height of the instrument (HI) is calculated using the rod. A rod person stands with the rod placed on top of the BM and the surveyor uses the level to shoot what is known as a back sight (BS). The number read on the rod by the surveyor is added to the know elevation of the BM; this gives the HI. After the HI is established, the rod person moves to some point (preferably a solid object no greater than 50' away from the BM) and places the rod on this point; this point is called a turning point (TP). The surveyor now shoots what is known as a fore sight (FS). The new number read on the rod is subtracted from the HI and the elevation of the (TP) is established. Next, the surveyor moves the instrument to a new location while the rod person stays at the TP. A BS is shot at the TP and the HI is again established. This process of establishing TP elevations and moving the instrument is repeated until the geographical point in question is established; now the open loop is completed. Once the elevation has been established the open loop must be closed. This is done to ensure that no errors occurred on the part of the surveyor during the survey. To close the loop the whole process is done in reverse. The rod person remains at the established elevation while the surveyor moves or changes the height of the instrument. Then the whole process is redone working back towards the BM using the derived elevation and the established TPs. The loop is closed when the survey and rod person calculate the BM elevation based on the established elevation of the geographical point in question. The calculated BM elevation is subtracted from the known BM elevation to give the survey error. While this sounds complex, the process is quite simple and after a few tries can be a fun thing to do.