8 Flashcards
What is the most commonly used surveying instrument for angle observation in the PAST?
Transits - simple form of theodolite with less precision, lacking scale magnification and mechanical meters, but light. Use vernier scales and external graduated circles.
Theodolites - consist of digital and non-digital. Use enclosed graduated circles and internal magnifying optical system. More precise
Total stations combine three components, what are they?
Electronic Distance Measuring (EDM)
Electronic Theodolite
Microprocessor
What can total station observe? From this data, what can they compute?
Slope distances, Horizontal and vertical angles
Can compute vertical and horizontal distance, elevations and coordinates
What does microprocessor do?
Assisting the operator step-step
Averaging the redundant angle and distance
Correcting observed distances
Making curvature and refraction corrections
Decomposing slope to hor and ver components
Calculating point elevations and coordinates
Parts of total station instruments
Telescopes - have reticles with cross hair and have peep sight
Eyepiece control knob - to focus the reticle
Objective control knob - focus the object
A clamp and tangent screw - enables the telescope to revolve horizontally and vertically
Tribrach - three screws for leveling, circular level, clamping device
Angle and distance’s relationship
Accuracy angle = accuracy distance/D
If known accuracy angle (“), find the accuracy distance by divide the angle with 206265” or 360/2phi to get unit of ppm
If known accuracy distance (no unit), find the accuracy angle by multiply the angle with 206265” or 360/2phi
How to observe horizontal angles?
For example, angle JIK. Put the instrument in the Middle point I, and J is the backsight with initial value 0, then turning to clockwise K is the frontsight (angle-to-the-right)
What is direction method?
Method to observing multiple horizontal angles by taking horizontal circle readings. Then, taking the difference between any two stations will result to the angle between them.
What is closing the horizon
Using direction method but including all angles around a point (so it makes circle). The final foresight point is the first backsight point and should be the same. Any difference is the misclosure.
Different of vertical angles and zenith angles
Vertical angle is measured up or down from horizontal plane ranging +-90degrees. It is ambiguous.
Zenith angle is measured down from the vertical axis and always clockwise. NOT ambiguous. Sum of direct and reverse angle = 360
Ex: see ppt 19
What is the formula measuring horizontal angle in total station?
If D<180 HRavg = (D + (R-180))/2
If D>180 HRavg = (D + (R+180))/2
What is used for sights and marks in total station
Prism poles (we use this), reflectors, reflective tape, tripod mounted targets
Explain prisms/retro reflectors (prism we used)
Measuring beams back to EDM for processing distance to ensure an accurate lengths greater than 3 km. Most prisms have an offset
Prolonging a straight line and Balancing in
PLEASE READ PPT 28 AND 29
With total station instrument, computed ………… can be obtained from ………..
Vertical distances (elevation) between points
Slope distances and zenith angles
