GPS Testing

During the GPS testing lab each team recorded the UTM coordinates 25 times at each of five points. After combining the readings I wanted to see if the results were statistically compatible or if they shouldn’t be compared. Another way to put it: are each team’s results form the same population or are there other factors that make the results not comparable.

There are some statistical methods to do this analysis. However, a simple way is to take the average of the eastings and northings, calculate the difference of each coordinate pair from the average, and plot the differences. The results should look like a scatter shot from shooting a target.

At point 5, the results seem to be randomly scattered around the average, or bullseye. The size of the spread is not very great.

Point 5 differences-corrected.jpg

Click on the thumbnail to see a larger version.

Point 1, on the other hand, shows the readings divided into distinct groups. Also, the magnitude of the differences is much greater.


All of the teams worked in the same time period, which means that GPS reception conditions must have been similar. The differences could be due to the differences between the GPS receiver units. More likely there was some variation in the operators or human error. I would recommend remeasuring this point to rule out human error.

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