How do I measure distances using a sub tense bar theoretically and practically?
ID: 1839054 • Letter: H
Question
How do I measure distances using a sub tense bar theoretically and practically? Are distances only horizontals or vertical? if yes, when we’re measuring a distance between two points on a slope can we just know the length of the slope (knowing the height) and directly compute the distance using either the pythagorean method or the trigonometric method(knowing the angle of the slope and the height) or are we supposed to break the slope into small steps and apply the previous methods on each step and then sum them to know the total distance. What is the effect of sag on the reading of measurements? ( can you please illustrate it by an example)How do I measure distances using a sub tense bar theoretically and practically? Are distances only horizontals or vertical? if yes, when we’re measuring a distance between two points on a slope can we just know the length of the slope (knowing the height) and directly compute the distance using either the pythagorean method or the trigonometric method(knowing the angle of the slope and the height) or are we supposed to break the slope into small steps and apply the previous methods on each step and then sum them to know the total distance. What is the effect of sag on the reading of measurements? ( can you please illustrate it by an example)
How do I measure distances using a sub tense bar theoretically and practically? Are distances only horizontals or vertical? if yes, when we’re measuring a distance between two points on a slope can we just know the length of the slope (knowing the height) and directly compute the distance using either the pythagorean method or the trigonometric method(knowing the angle of the slope and the height) or are we supposed to break the slope into small steps and apply the previous methods on each step and then sum them to know the total distance. What is the effect of sag on the reading of measurements? ( can you please illustrate it by an example)
Explanation / Answer
the subtense bar is an instument used for mesuring horizontal distance between stations
subtense bar method is an indirect method of distance determination this method essaantially consists of mesuring angle sutended by two ends of horizontal rod of fixied lenth called subtense bar which method tripo dos not nessessary and required ordinarytransisters it is having a lenth of2 m it is having dia of 20cm bals at the end of the barsand is made perpendicular to the bar.
procedure :setup the insrument at benchmark if no bench mark avalible the fly leveling mey be done on the other staion reference to any predetermened pont as rl of the sataion.
theritically we can mesure distence by extending lines to the ground and mesure the distance with sutable scale
practially by means of tacheometer relative distance beteween sations of differentRL values can be computed by instument stationsby taking observations vertical angle step readings before stastarting the survey area to be roughly and main stations are selected accoourding to mesure of area
yes we van determene horizontal distance by using subtense bar and we van mesure vertial distance also but not accurate value.
effect of sag: if we are going to mesure longer distances sag may occure it is due to various resons like wind temperature changes and weight of the tap or chaine we have to correct the value by using some statderd farmule. some times due to sag we get more distance value the actual some times less then actual. so effect of sag is to be corrected and in chaine surevy it is very high.
example:in case of road alignment we double cross this situations like different rl and uneven ground type in this case we can use subtense bar method and in this case we can to fine the sloped distance by using someny method like pythogras method or trignometric method or equal traingles method or simpson rule also by using this above methods we can easyly get the solutions
thank you
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