LAB 2 TRAVERSE ANGLE, AZIMUTH, and DISTANCE MEASUREMENT

HW Leveling (NOTE: use ordinary single wire methods) Objective To perform differential leveling to measure the elevations of the “parcel corners.” Students will learn proper use of a level and how to run a closed level loop, including adjustments of elevations for turning points in the loop. Equipment Automatic level and level rod.

Procedure 1. Learn proper setup of level and how to correctly read the level rod. 2. Find a suitable Bench Mark near your parcel. Search the NGS data sheets for bench marks. Search local BM listings. If there are no published vertical control “bench marks” nearby, you may use the published elevation for your “base control point (X)” as a bench mark. Even though this elevation may not be of high accuracy, we will use it anyway for convenience. 3. Starting at your Bench Mark, run a closed loop line of levels including all four parcel corners as turning points, closing back onto your Bench Mark at the end of the loop. Do not sight a parcel corner as a "side shot", make sure it's a turn point. 4. In making your “level run”, choose good turning points (if you need intermediate turning points). A turning point should be a discrete point that you may readily come back to (find again). This is where the rod is to be placed, NOT the level. You should NEVER place the rod randomly on the lawn or in the middle of a sidewalk slab. It is the rod person's responsibility to locate good turning points. Some good examples include: a. particular point on manhole covers, b. water valve covers, c. high corners of sidewalks, d. corners of planter boxes. 5. Make an Excel worksheet of your field measurements and calculations. Make the worksheet looks like standard level notes presented in lecture or in the text. 6. Reduce your notes to determine your loop misclosure. Your measured elevation of the Bench Mark at the end of your loop compared to the known published value of elevation. 7. Perform an error analysis to determine acceptability of loop misclosure. a. Calculate allowable misclosure (dependent upon number of instrument setups): allowable error = 0.003 m (or 0.01 ft) times the square root of N, where N is the number of instrument setups in your loop. b. Compare actual misclosure with the allowable and come to a conclusion as to whether you have an acceptable level run, or if there are blunders. 8. Balance the level run. If the misclosure is acceptable, distribute the closure error by the method discussed in section 5-6 of text based on the number of setups. Divide the total error of closure by the number of setups to get a correction per setup. Apply the corrections to the loop points starting at the first point getting one correction, the second getting two corrections, etc. until all preliminary elevations have been corrected. Be sure that the final, adjusted elevation of the benchmark is the same as the initial elevation. This will give you the final adjusted elevations for your parcel corners.

For example, if the loop has 5 setups with an error of +0.05, the basic correction is therefore: Corr = - .05/5 = -.01. The first point would be adjusted by -.01, the second by -.02, the third by -.03, etc.

Submit: Upload your Excel spreadsheet in WebCT using the Assignment tool. In your spreadsheet insert text boxes or write the following into cells: discussions of your process, observations, results, misclosure and adjustment calculations.