How do you find the elevation of a point?

Answer 1

(Another contributor wrote:)

Introduction :

To find the elevation of any point we have a some way one of them is closed level circuit , which in this way we can cheCk our result .

And we can apply this method in the place that we cannot find difference elevation between them by sample leveling because of the distance between the points and their large difference elevation of the points .

to the sighting distances between the two points is to great for the leveling staff to be read , because the sighting distance from instrument to staff is depending upon the purpose of leveling and the required accuracy . in ordinary leveling operation the maximum length of sight should not exceed about (75 m).for precise leveling with the engineer is level , sights should be limited to about (30-50)m.

In this way we must divide the distance between the two main points in two some station and detect the middle of any section two setting up the level instrument at these place .

The only difference point between first and second type of closed leveling is that here , his not equal to zero and it is equal to the difference of elevation of first and end point of the line so at the first type.

Aim of the test

1. to determine the elevation of the point from a known point elevation .

2. checking the the elevation of the first point .

3. find the height of the point by a large accuracy and repair reading error .

Advantages

1. at applying any method of leveling we cannot finish the process without making mistakes ,so this way help us to reduce this mistakes by starting the process from a point which its elevation is known and ending the process at the point .

2. we can calculate the difference elevation between two points that their distance is greater than tha allowable distance that we can do it by one leveling process .

Equipment

1. level instrument

2. staff

3. tripod

4. chalk

5. tape meter

Procedure

At the first time we must find the two points that we want determine the difference height between them , after that we will divide the distance between the points to two or more section , this is because it that we cannot find it by one level process, after that we detect some other place to return to the first point that is to know the ratio of errors that we have made at applying the work.

Then we will detect the center of each section to setting up the level instrument at this point, at this time we must apply the midpoint leveling, because it's a best method for leveling at high accuracy. Then we can read the first point (back sight 1) and read the second point (fore sight 1). After that we must change the place of level instrument to second section and setting up the level at the center between (foresight 1 ) which in this step called (back sight 2) and (fore sight 2).

The point of (f.s 1)and (b.s 2) is known as turning point .

We will complete the other section such as the previous process.

At the last to determine the difference elevation between the two main points( ∆H), we must sum the difference elevation of each section ( ∆H= ∆ h1+ ∆ h2 +∆ h3+………+∆ hn), and at last the summation of all (∆H) must be equal to zero, but it is allowable to make errors till (20 mm), but if the total of all errors more than allowable error, the process must be refused.

Calculation

Station 1

Distance between A & B= 22 m

Point A B.S 1=1.403 m

Point B F.S 1=1.361 m

∆h1= B.S 1- F.S 1 = 1.403 - 1.361 = 0.042 m

Staition 2

Distance between B & C= 28 m

Point B B.S 2= 1.678 m

Point C F.S 2= 1.020 m

∆h2= B.S 2- F.S 2= 1.678 - 1.020 = 0.658 m

Staition 3

Distance between C & D =12 m

Point C B.S 3 =1.938 m

Point D F.S 3 =0.785 m

∆h3 = B.S 3- F.S 3 = 1.938 - 0.785 = 1.198m

Staition 4

Distance between D & E =16 m

Point D B.S 4 = 0.557 m elevation= 103.477 m

Point E F.S 4 =1.788 m

∆h4 = B.S 4- F.S 4= 0.557 - 1.788 = - 1.231 m

Station 5

Distance between E & F = 30 m

Point E B.S= 0.310 m

Point F F.S= 1.954 m

∆h5= B.S5 - F.S5 = 0.310 - 1.954 = -1.644 m

Station 6

Distance between F & A =28.9 m

Point F B.S 6= 1.972m

Point A F.S 6= 1.005m

∆h6= B.S 6 - F.S 6 = 1.972 - 1.005 = 0.967 m

Discussion

At this test we talked about one of the leveling methods which it is the closed series level circuit.

In this test we determined the distance in elevation by closed level circuit, at any leveling process we have made some errors that is caused from the number of station or wrong reading the point by the students, and the weather was not suitable for working because it was cold there was strong wind at that time. At ending the report we knew that that our amount of error was equal to (0.010 m) that it is less than global standard allowable error that is (0.020 m),

Sources of errors

1. personal error

2. instrument error

3. natural error.