Lab Nine: Survey Grade GPS Data Collection

Introduction

This lab is an introduction to high accuracy survey grade GPS techniques. With the use of a Topcon survey grade GPS, points were collected, classified and imported as a feature class in ArcMap. These points were then used to create a cartographically correct map of each different feature type that was collected.

Methods

Map one. Survey grade GPS study area. 

Figure one. Dr. Hupy (right) instructs students how to use a Topcon survey grade GPS unit.

The collection of points for this survey were conducted over a period of about two hours via pairs of students. Each pair were instructed in the use of the GPS unit, collected and classified points (figure one). All points were collected in the area around Phillips Hall, an instructional building located on the University of Wisconsin Eau Claire campus (Map one). This GPS unit is unlike the other ones used in this course as is not a single piece of equipment. It is a collection of individual parts which work together to record locational data. The satellite signal receiver is yellow and grey apparatus at the top of the black pole in figure one. The screen in the center of the image is the central computer, but it could be replaced with a modern mobile device with the correct software installed as all communication between the computing unit (screen) and the GPS receiver is done through a Bluetooth connection.

When collecting points the GPS unit had several features that were calibrated by Dr. Hupy before students were allowed to collect points. First off was how many position readings were collected for each point. There were two settings for this: Quick reading and precise reading. With quick reading 20 GPS positions are recorded then averaged for each individual survey point. Precise readings go through the same process as quick, the only differences being that 30 readings are averaged for each survey point and that all attribute data must be entered for an observation before another point can be recorded. The amount of readings for each point in both quick and precise reading modes can be specified by the GPS operator. The GPS operator is also able to specify the length of the pole to compensate for the receiver’s height above the ground. In this case the pole was two meters tall.

Another notable feature of a survey grade GPS unit is its accuracy when compared to other lower cost/quality GPS units. For this Topcon unit there were three accuracy settings.

1. Auto: Accurate to 5 meters of actual location. This accuracy rating is comparable to what one might get from a handheld GPS device not unlike the ones used for earlier labs in this course. This reading was found most often when the GPS unit was close to a building’s wall.

2. Floating: the accuracy of flouting about 2.5 meters, a bit better than Auto. There is still much room for improvement.

3. Fixed: The GPS has a good single allowing it to be accurate to less than five millimeters.

Figure two. Creating a new feature class using XY coordinate data from a table. 

 Once all points were collected they were exported from the GPS computing unit as a text file which was  then imported to ESRI ArcMap as a new feature class by using the data tables XY coordinate values (Figure two). The projection was defined as WGS84 UTM zone 16 before the points were imported. From here, it was a simple process to symbolize and map the data.

Results

Map two. Symbolized results of high accuracy GPS survey. 

The resulting points displayed a high level of accuracy. One can note this when observing the patterning of the light poles across Phillips Parking Lot. They form a gentle arc that conforms to the shape of the lot. With a lower accuracy GPS unit one would expect the poles to hardly be linear in their patterning or consistent in their spacing. Unfortunately, this is one of the only consistency between this base map and the survey points. In other places, such as the smaller parking lot just north of Phillips Lot, the accuracy is not as good. The GPS cannot be faulted for this; its accuracy was well under a detectable amount on this map. The problem is the generously generalized base map used for this display of data. High-resolution aerial imagery would have been a better choice for accuracy but would have resulted in confusion of data at this scale, as the GPS recorded features would be overlaid on their visible real world counterparts.

Conclusion

This project entailed using a GPS receiver to collect points at a high level of accuracy. There were several different accuracy levels and many customizable settings on the GPS unit for data collection. The data was then collated and distributed as a text file including each survey point’s coordinates and feature classification. This data was then digitized to create a map that symbolized all the collected data. In all this assignment reinforced the student’s understanding of GPS data collection techniques by introducing them to using a survey grade GPS unit.