SO503 Spring 2007

GPS Survey Lab

You will survey as follows:

Go to Bench Mark (BM) on the seawall near Hendrix (direction and coordinates on the last page of the link below).

Collect 500 readings at the BM.
Return to the lab, and download your data. MICRODEM provides access to a program that communicates with the Garmin GPS. Save the data as a DBF file which you can import into EXCEL.

You will calculate and discuss the following for your lab report. For all calculations use the UTM coordinates, these are an orthogonal grid that lets you perform simple calculations to get distances. You can use printouts from EXCEL, without insuring that the x and y scales are the same.

What is the best estimate of the position of the bench mark?
What is the average error for each reading, if you assume that your best estimate is correct?
How far away from the “true” NOAA value of the benchmark is your average location?
Get a histogram of the total error (no sign), and the errors in easting and northing (signed) (directions below).
Get a cumulative error plot (example below).
Estimate the CEP for a reading with this GPS receiver, and the 1s, 2s, and 3s 2DRMS values. Discuss any factors that would bias these results as accurate estimates of the accuracy of this GPS unit.

Measure	Percentage within Radius
CEP	50%
1s 2DRMS	63%
2s 2DRMS	97%
3s 2DRMS	99+%

Santee Basin Bench Mark

Source:

Histogram Creation

(Optional; you must do once if you don't see the menu choice in the next step. This is probably the case on your own computer, but should not be the case in the lab.) Go to Tools, Add-Ins, and insure that "Analysis ToolPak" is checked; it might have to be installed.
Go to Tools, Data Analysis, and select "Histogram"
For help, look in the index for "Histogram analysis tool". In particular note that you need a block of cells which define the bins you want to use.
If you want the graphical histogram, you have to check the box. By default it is turned off.