L10Sep16

# L10Sep16 - Reciprocal Levelling Let the true difference in...

This preview shows pages 1–3. Sign up to view the full content.

CIVL 1009 Survey (2010-2011 Semester 1) Chapter 1 Differential Levelling 61 Reciprocal Levelling Let the true difference in levels between A and B be δ H, c 1 be the effect of collimation error between A and B, and c 2 be the effect of collimation error between B and A At instrument position I 1 , δ H = a 1 – ( b 1 – c 1 ) (1) At instrument position I 2 , δ H = (a 2 – c 2 ) – b 2 (2) Adding Equation (1) and Equation (2), we have δ H = 0.5 [(a 1 – b 1 + c 1 ) + (a 2 – c 2 – b 2 )] = 0.5 [(a 1 – b 1 ) + (a 2 – b 2 ) ] (since c 1 = c 2 , given the same offset distance, e.g. 5 m) = 0.5 (Apparent Difference 1 + Apparent Difference 2 ) CIVL 1009 Survey (2010-2011 Semester 1) Chapter 1 Differential Levelling 62 Reciprocal Levelling Let the true difference in levels between A and B be δ H, c 1 be the effect of collimation error between A and B, and c 2 be the effect of collimation error between B and A At instrument position I 1 , δ H = a 1 – ( b 1 – c 1 ) (1) At instrument position I 2 , δ H = (a 2 – c 2 ) – b 2 (2) Subtract Equation (2) from Equation (1), we have 0 = a 1 – (b 1 – c 1 ) – (a 2 – c 2 ) + b 2 -2c 1 = (a 1 – b 1 ) – (a 2 – b 2 ) (since c 1 = c 2 , given the same offset distance, e.g. 5 m) e = 0.5 (Apparent Difference 2 – Apparent Difference 1 )/ L CIVL 1009 Survey (2010-2011 Semester 1) Chapter 1 Differential Levelling 63 Errors in Levelling Computation of errors Collimation error Curvature of the Earth • Refraction Precaution Start and finish at the Stations with known reduced level ( closed loops ) Sight length should be less than 60 m Lengths of Backsight and Foresight should be the same Readings should be booked immediately (Upper Stadia, Mid-Hair, Lower Stadia) Staff vertically checked by circular bubble or rocking of the Staff CIVL 1009 Survey (2010-2011 Semester 1) Chapter 1 Differential Levelling 64 Contouring

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
CIVL 1009 Survey (2010-2011 Semester 1) Chapter 1 Differential Levelling 65 Contouring Definition A contour is a line drawn on a plan joining all points of the same height above or below a datum (equal altitude) Contours cannot cross, split or join other contours, except in the case of an overhang, e.g. a cliff The height between successive contours is called the vertical interval or the contour interval • Value of contour interval depends on the variation in height of the area being contoured • The contour interval is kept constant for a plan or map The plan spacing between contour line indicates the steepness of slopes • Closely spaced lines indicates a steep gradient
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern