Geomorphology Lab 1  GPS

The report is due Friday 31 March.  Reports are to be neat, typed in 11-12pt font.  Multiple pages must be stapled together.  GPS books need to be handed in at the same time or the lab will not be accepted.   Late submissions will have points deducted.

1.  Measure the location of the 4 points around the Harrison athletic field, number them 1, 2, …using the GPS in UTM mode. Take 5 GPS measurements at each location.  Also pace out the distance between points.  You must know your pace.

2.  To help you with question (4), make an approximate map of the building location and include the location of the measurements with respect to the building location.

3.  Plot the points on an x-y graph with north up and east to the right.  First, plot your paced values, in meters, from the origin at point 1 (value 0,0).  North and East are positive.  Your paced values will be your reference because you know the distance and direction and have an intuitive sense of how it should plot.  Leave plenty of room for the UTM points because they can be a bit wild.   Label the points (1, 2, ..) and connect with a solid line. 

Next plot the GPS values on the same graph as the paced values. BUT FIRST, find the average value for North and East for each set of measurements at each point.  Since the UTM numbers are distance in meters in each UTM zone (60 zones cover the earth), the distances are huge. To keep the numbers small, use point 1 as your origin.  That is, subtract the average value of point 1 from all the values including that for point 1.   Therefore, point 1 will have coordinates of 0 N and 0 E.  Points 2,3,4 will also have relatively small numbers in the hundreds at most.  Label each point and connect with a dashed line. 

When plotting the GPS positions don't forget the error bars.   For our purpose, the error will be calculated as the maximum value minus minimum value (for the 5 values recorded) divided by 2.  Thus, the length of one arm of the error bar is the half the total range of values at each point.   The errors in the north - south direction might be different than the east-west direction, and consequently, the length of the error bars will also be different.

4.   Compare the measured distance (paced) and expected geometry to that found by GPS.  Discuss the results.  Include in the discussion an examination of possible errors and their relative importance.

5.   If the location of the four points were each 1 km apart, how well would your GPS measurements reproduce the overall pattern of points?   How about if the points were 10 km apart?   The purpose here is to get you to compare the magnitude of the GPS error (or any instrument) to the magnitude of the absolute measurement.  Or in other words, how important are the errors relative to what you want to measure?