RE-ESTABLISHMENT OF TWO PRIMARY CONTROL BEACONS

SURCON QUESTION: YOU HAVE BEEN ASSIGNED THE RE-ESTABLISHMENT OF TWO PRIMARY CONTROL BEACONS ALONG A BUSY URBAN ROAD. WHAT OFFICE AND FIELD PROCEDURES WILL YOU ADOPT IF THERE ARE SIMILAR CONTROL WITHIN 2000 METRES OF THE LAST BEACONS? GIVE AN INVENTORY OF SURVEY EQUIPMENT TO BE USED. WHAT CORRECTIONS WOULD YOU APPLY TO YOUR MEASURED DISTANCES?

COMMENT: This is a 1996 question. GPS equipment was not in use in the country in 1996, so the examiners expected the answer to enumerate control extension using rigorous high-order traversing.

Office Planning

Planning for the survey shall begin in the office, where the coordinates of the control points shall be searched and a topographic map of the project area shall be studied.

Field Reconnaissance

The existing controls shall be located on the ground. Appropriate and intervisible points shall be identified. These points shall serve as intermediate points on which traverse shall be run to the probable location of the lost control points.

Equipment Selection

In order to carry out a high-order traversing, the following equipment shall be needed:

1.      Wild T3 of 0”.2 least count

2.      Targets mounted on tripods

3.      Optical pluments

4.      EDM equipment

Field Procedure

Horizontal angles shall be measured with Wild T3 measuring 0”.2.  All angles will be observed on face left and face right equally spaced round the circle. The minimum number of positions shall be 16. Observations shall be made by night.

The theodolite, EDM and targets shall be centred to within 1mm over the survey mark using optical plummet.

Bearing shall be controlled by azimuth observations taken every 10 stations. Azimuth closure at azimuth check points must not exceed 1”. 5 per station.

Heights shall be observed by spirit leveling. Distance shall be measured with EDM equipment with temperature to +1^oC and pressure to +5mm of mercury at both ends of the line.

The traverse shall close back on the existing control. Position closure shall be within 1:100,000.

Corrections to be applied to measured distances shall include:

1.      Instrument constants

2.      Reflective index correction

3.      Slope correction

4.      Sea-level correction

5.      Arc to chord correction

DISCLAIMER: This material is only an attempt to answer an examination question, though written from a background of solid knowledge and practical experience in Surveying and Geoinformatics. It has not gone through peer review. Therefore, all views and opinions expressed therein remain the responsibility of the author and do not necessarily represent that of any institution.  Feedback on corrections and constructive criticisms should be sent to tolutaiwo75@gmail.com. Thank you.