C. Line Directions

1. Traverse Direction Computations

After angles are balanced by whatever method selected, the direction of each traverse line must be determined.

The direction of one line must be known or assumed and by using horizontal angles other successive line directions are computed. The computations were discussed in the Directions topic. Ususally, the same type of angle (interior, deflection, etc) is measured on an entire traverse which can simplify computations somewhat. 

a. Computation Method

There are two approaches to compute directions around a traverse: tabular and sketching.

While the tabular method is an efficient systematic approach, for the surveying neophyte it can be confusing and all too easy to flip quadrants. It's not easy to determine if computed directions make sense since there is no visual indication.

Drawing sketches, which was covered in the Directions topic, is slower but allows the surveyor to see line relationships and provides a graphic computations check. 

Which to use is largely a matter of preference, but for the beginner sketching is generally a better way to start. All the traverse direction examples and comps in the Surveing Library use the sketching approach.

b. Math Check

Whenever possible, we want to include a math check to catch computation errors.

A loop traverse provides a math check because it closes back on itself. Starting with the first line, we sequentially compute directions around the traverse and then close back on the first line. Its computed direction should match its starting direction. If not, there is a math error (or unadjusted angles were used by mistake). 

A link traverse doesn't have a math check unless the directions of its first and last lines are known. This generally insn't the case for most link traverses even if they begin and end on known points. Link traverse computations are covered in Chapter H. Closed Link Traverse.