Once upon a time.. GY 301: Geomorphology. Alidade & Plane Table. Ray Measurement Geometry. Measurements with the Alidade and Stadia Rod

Transcription

1 UNIVERSITY OF SOUTH ALABAMA GY 301: Geomorphology Once upon a time.. The Alidade and Plane Table Surveying Lecture 10: Total Station Surveying Alidade & Plane Table Measurements with the Alidade and Stadia Rod Stadia Rod: usually a 10 foot rod with feet and 0.1 foot divisions painted on the rod An early model alidade Geometry of Alidade Measurements Stadia : distance on rod from lower to upper horizontal stadia line; distance ratio is 1:100 ALIDADE STADIA CROSS HAIR Ray Measurement Geometry Measurements from the alidade station to a data point are termed rays The ray is drawn on the plane table to track distance and direction, and the elevation of the ray endpoint is calculated in field notes A correction must be made for the difference between the alidade cross hair (CH) and the instrument height (IH) of the alidade (see below): full stadia 10 vertical cross hair 9 half stadia horizontal cross hair IH=3.5ft Cross hair (CH) = 5.7ft 5.7ft 8 quarter stadia stadia rod stadia = = 2.4 feet distance = 2.4 x 100 = 240 feet quarter interval cross hair Elevation=161ft Rod = 161ft + (IH-CH) = 161ft + (3.5ft-5.7ft) = 161ft 2.2ft = 158.8ft 1

2 Alidade Mapping Strategy You should not try to shoot a ray > 250ft with the alidade unless you have no choice Moving the alidade from one station to another station is traversing the instrument You should shoot rays to all needed control points around the 1 st station, then shoot the last ray to the new 2 nd station position You will need to calculate the elevation at the new 2 nd site, and start a new data sheet with a new instrument height recording Since you are to produce a topographic map you may need supplemental elevation control points in addition to the feature that you are mapping (geological contact, building plan, etc.) R1 R7 ST2 R6 ST1 R2 R4 R3 R5 Today s Agenda The Total Station Benefits and Downfalls The instrument Total Station Electronic version of Alidade Accurate to ±3 ppm horizontal & vertical 3x10-6 (5000 feet) = 0.2 inches Results are stored in a data collector computer that can display results graphically 2

3 Results are stored in a data collector computer that can display results graphically Each individual ray shot can take as little as a few seconds to take- many more stations can be collected per day as compared to the alidade and plane table method It may take 30 minutes to an hour to set up (level) the instrument before data can be collected It may take 30 minutes to an hour to set up (level) the instrument before data can be collected Battery life on data collector computer can limit length of daily surveys Total Station Surveys Total Station Surveys A backsight target is established north of the starting station position to calibrate coordinate system 3

4 Total Station Surveys A backsight target is established north of the starting station position to calibrate coordinate system If two benchmarks or former station positions have known coordinates the relative positions can be used to calibrate coordinate system Setting up the tripod Setting up the tripod Setting up the prism Packing/unpacking the instrument 4

5 Total Station Output Data recorder Upcoming Stuff Homework GPS Data processing (Lab 4 due a week Friday) Signup for data transfer/software instruction Next Lecture: Total Station setup demonstration Friday s Lab: Outside: Total Station survey (meet first in LSCB 042) 5