Report

Types of angles Z A L M MLN – Horizontal angle ALM – Vertical angle NLB – Vertical angle ZLA – Zenith angle ZLB – Zenith angle R N B The theodolite Measure: vertical and horizontal angles • Main components - sighting telescope, horizontal and vertical circles and leveling system. Horizontal (Trunian) axis Line of sight Vertical axis Axis of plate level In a well condition theodolite • • • • 1- Line of sight axis + H-H axis 2-H-H axis + V-V axis 3- V-V axis + L-L axis If these axis are not perfectly perpendicular , errors in angles will occur • To reduce these errors the mean of the face left and face right reading is taken Types of theodolite • 1- Optical reading theodolite • 2- Digital reading theodolite • The total station : Digital reading theodolite • • +EDM( electronic distance measurement device ) + processor and memory Major Components of a theodolite • • • • • Telescope Vertical circle+ horizontal circle Horizontal/vertical clamp Horizontal/vertical slow motion screws Plate bubble (Level tube) Optical reading theodolite Setting up a theodolite • • • • • Centering Levelling Elimination of parallax Sighting the target Reading the angle Measuring horizontal angles • Sight point A on face left • Set reading on horizontal circle ( e.g. 00 00´ 00˝) • Direct the telescope to point B and record ‘face left’ directions (e.g. 35 26´ 20˝) • Reverse the telescope to ‘face right’ and read direction to point B ( 215 26 40˝) • Back to point A on face right and record the reading (180 00 20) In the figure, the horizontal angle was measured at B to C and A. Compute the angle CBA. Station at Station observed B C A Face left deg 00 83 min 03 50 Face Right sec 20 10 deg 180 263 min 03 50 sec 50 40 A B C Errors in Angle Measurement • Mistakes –pointing, setting up over the wrong point, booking, reading • Random – settling of tripod, wind, temperature, refraction • Systematic/instrumental – Horizontal axis not perpendicular to the vertical axis – Axis of sight not perpendicular to the horizontal axis – Axis of the plate bubble not perpendicular to the vertical axis. Total station ZA (Line of Sight / Collimation Axis) SA (vertical axis :Standing Axis) KA (Trunian Axis) V (Zenith Angle) VK (Vertical Circle) Hz (Horizontal Angle) HK (Horizontal Circle) HEIGHT OF REMOTE POINT SD (Slope Distance) HD (Horizontal Distance) dH (Difference of Height) hr (Height of Reflector) hi (Height of Instrument) E0 (Easting of Station) N0 (Northing of Station) H0 (Height of Station) E (Easting of Target Point) N (Northing of Target Point) H (Height of Target Point) (zenith angle ) . Vertical angles V%. The vertical angle • Is the angle above or below a horizontal plane through the point of observation • The angle above the horizontal plane is +ve vertical angle (angle of elevation) • The angle below the plane is –ve angle (angle of depression) Measuring vertical angles Theodolite is set over point P the following vertical angles circle readings were recorded on targets at points A and B. Calculate the vertical angles to points A and B Point observed F.L F.R Reduced F.L Reduced F.R Mean vertical angle A 85 36´ 274 28´ 4 24´ 4 28´ 4 B 98º 48´ 261 08´ -8 48´ -8 52´ -8 50´ 26´