LAB 2 TRAVERSE ANGLE, AZIMUTH, and DISTANCE MEASUREMENT s1

LAB – GPS Measurement of Position

Objective Students will gain experience collecting spatial data using an inexpensive, hand-held G.P.S. unit. This lab is the first of two homework assignments designed as an experiment to determine the accuracy and precision of the GPS instrument.

Procedure 1. Obtain a GPS unit. Small handheld models can be bought for as little as $100 or can be borrowed from anyone who has one for navigation, hunting, hiking, etc. Some phones have built in GPS. You may also use mapping or survey grade units if available. 2. Follow the instructions for your unit to learn how to use it to get a position. Set the unit to collect positions in the same coordinate system as your traverse control points, so that the final coordinates you measured for your parcel corners will be in the same coordinate system and datum as the GPS. 3. You are to measure your parcel corner coordinates in the Universal Transverse Mercator (UTM) coordinates on the NAD 83 (or WGS84) datum, units in meters. 4. Collect 10 observations of position (1 observation / every minute for a hand held GPS) at each parcel corner of your traverse. Record your data in an Excel spreadsheet. 5. Collect 10 observations of position (1 observation / every minute) at the same two control points you used as control points for your traverse. 6. Check: Total number of points observed = 6, Total number of observations = # of points*10

Analysis: 1. Observe the PRECISION of your GPS data points. For each point, plot the measured GPS positions on an X, Y (Easting, Northing) chart (use an Excel spreadsheet X, Y scatter chart). You can make preliminary “hand” plots on grid paper if you wish, but turn in your Excel spreadsheet charts for grading only.

QUESTION #1: Since your GPS positions were gathered over a spread of time, do the positions seem to “drift” with time, or are they random? Also, do they represent a "circular cluster? or "highly irregular cluster"? or "long drawn out cluster"? Answer this as an essay answer on a separate MS Word document.

2. Observe the ACCURACY of your GPS points relative to your two known geodetic control points. On your plots for each control point, add the “known” position as published for the control station.

QUESTION#2: Inspect the pattern of GPS positions relative to the “known” published value. Discuss the pattern you have at each station. A circular scattered pattern centered over the “known” point? A circular scattered pattern removed somewhat from the “known point”? Something else?

3. Identify and remove blunders from your GPS data points. Observe your cluster and identify any GPS positions clearly far out of the pattern of the remaining “good” positions. The "far out" distance is two or three diameters of the general cluster size.

QUESTION #3: Discuss whether you had blunders. Which did you throw out and why?

4. Calculate the MEAN positions the parcel's corners. After removing any obvious blunders, calculate the mean X and mean Y of the parcel points. This is your mean GPS position.

4. Submit for HW:

1. An MSWord document that has three parts: a. A general description of your equipment and field procedures. b. Tables that present your raw data c. Your answers to the essay questions.

2. An Excel spreadsheet showing charts for each of your stations indicating the measured positions for all points, along with the “known” point at the geodetic stations.