Question

Make a comparison between using one Theodolite for layout different horizontal curves types and using Two Theodolite method, taking in consideration possible obstacles and the specialty between horizontal curves types

Answer 1

A Theodolite is a surveying instrument , which can measure horizontal and vertical angles with a rotating telescope .

Using One Theodolite method

• One Chain or a Tape is required in addition to one Theodolite.
• Tangential angles set out the curves.
• The ground should be fabourable for accurate chaining.
• The method of deflection angles is used
• This method is more commonly used because it requires only one surveyor .
• The points are marked until the end of the curve.
• In case of a left handed curve , each of the values for total angles should be subtracted by 360

Using Two Theodolite method

• It requires two theodolites and doesn't require a chain or a measuring tape.
• This method is based on the property of a circle in which 'the angle between the tangent and the chord is equal to the angle which the chord demarcates in the opposite segment.
• The points are marked from both ends till they meet at the centre of the curve.
• This method is not used as much as one theodolite method because it requires two surveyors.
• If the ends of the curve are not visible from one another then , the vernier is set to read an angle of 360 - (Angle between them/2) + Total angle , for each points respectively.