1Compass Techniques I. The Brunton Compass A. Parts of the Brunton Pocket Transit 1. compass- measuring magnetic bearing 2. clinometer- measuring vertical inclination of planes 3. hand level- sights for line surveying a. mechanisms (1) clinometer level = use for taking vertical angles (2) bullseye level = use for taking compass readings (3) graduated circle (4) compass needle (5) sighting arm (6) sighting window (7) declination adjusting screw (8) lid with mirror (9) lift pin/needle brake B. Making Compass Readings 1. Set magnetic declination a. use adjusting screw b. refer to topo map or mag. dec. charts 2. Compass bearings = line orientations in space relative to geographic directions (quadrant vs. azimuth methods) a. open lid with sighting arm extended b. center bull's eye bubble c. align compass along desired line d. read bearing indicated by white end of compass needle e. check bearing and record (1) warnings: watch for magnetized objects that could alter compass reading (a) Fe-rich rock bodies can only use sun compass C. Using clinometer 1. align vertical edge of compass with angle of plane 2. adjust bubble level of clinometer 3. read angle from vernier scale on compass D. Computing vertical elevation 1. measure eye height from ground surface (E.H.) 2. sight compass to top of object (e.g. top of a pole) 3. adjust vertical bubble level and read angle (theta) 4. measure horizontal distance from compass point to object (H.D.) 5. solve: total vertical height of pole = (H.D.)(tan(theta)) + E.H.2 E. Measuring horizontal distances 1. measuring wheel 2. tape measure 3. pace estimation F. Using Hand Level to Measure Elevation Differences 1. set compass clinometer to 0 2. open compass with sight and lid mirror toward eye 3. measure eye height (E.H.) 4. sight up slope, keep track of no. of moves and no. of E.H. G. Measuring Strike and Dip 1. Definitions a. Strike = line connecting points of equal elevation on planar surface (e.g. rock bed) (1) line bearing as azimuth or quadrant b. Dip = vertical angle of inclined surface, measured down from horizontal, perpendicular to strike (1) vertical angle + direction of dip c. Orientation of Lines in Space (1) Trend: compass bearing of line in space (2) Plunge: vertical angle from horizontal, and direction of angle in space 2. Methods of Measure a. sighting b. direct measure H. Compass Bearings 1. Bearing- the direction from one point to another, usually expressed in degrees east or west of true north (quadrant method) or in degrees from 0-360 (azimuth bearing) where north is 0o or 360o, east is 90o, south is 180o, and west is 270o. 2. Measuring Bearings- To determine the bearing/direction from one point to another do the following: a. Draw a line from the first point to the second point b. using a protractor, center the origin of the protractor on the first point, align the bottom edge with the bottom edge of the map, and the 90 degree tic parallel with true north at the top of the map. c. Read the angle between north at the 90 degree mark of the protractor, and the line between the two points in question. 1. give answer in either the quadrant or azimuth