Fore Bearing

The line is measured in the forward direction .i.e. along the progress of survey is known as Fore bearing. Fore bearing = BACK BEARING±180.

Fore bearing columns

The fore bearing measures the absolute compass angle to the next station. Several formats are supported. Some other entry modes will change the column heading and the interpretation of the data entered. If a back bearing exists the Fore Bearing and Back Bearing are averaged to calculate the coordinate of the next station.  A magnetic deviation from north can be entered in the Horizontal angle reference dialog. It is also possible to change absolute angles to turning angles to minimize the influence of local magnetic attractors.

Traverse Window Columns

Each station references two rows of data entry cells: the lower row and upper row (the lower row contains station or station Index). Data stored in the lower row is assumed to occur at the station, e.g. ground type or side shots. Data in the upper row is assumed to occur in between stations.

It is possible to create own column for storing extra attribute data, in addition to the default columns that already exist in the survey Notes. The various columns can be added or removed to the survey.

Calculation of corrected bearings and Internal Angles

Theoretical difference between fore bearing and back bearing should be 180°.

Local Attraction

If the difference between magnetic Fore bearing and back bearing of the line is not exactly 180°, It may be due to presence of local attraction at one of the both stations. If this difference is exactly 180°then both stations are free from local attraction.

Practice problem

In the below table observed bearings are given, we will compute the corrected bearings and internal angles.

No line has a distance of exactly 180° between fore bearing and back bearing. In such case, a line where the difference is closest to 180°is selected and is called least disagreement, for this line correction is assign to each of the two stations of that line with opposite side. Now, we will compute internal angles from these corrected Bearings.

A = (360° - 316° 30′) + 70° 30′ = 114° 00′

B = 327° 30′ - 250° 30′ = 77° 00′

C = 257° 30′ - 147° 30′ = 110° 00′

D = 136° 30′ - 77° 30′ = 59° 00′

Questions:

• What is fore bearing?
• How much should be the theoretical difference between Fore bearing and Back bearing should be?