Team 8 GPS Project
CAEE 211 - Winter 2008
Rebeka Van Derzee
We believe that the core purpose of this assignment was to learn about GPS systems through hands on experience. To gage our learning progress we have each provided our initial understandings of what GPS is/does. With this in mind our objectives for this project were to research and operate a GPS device by creating relevant project scenarios. These scenarios involve the application of the device's features to better understand all the systems capabilities. While brainstorming ideas for our project we decided to incorporate three 'mini' projects into our report. Creating three different projects enabled smaller two person teams to work directly with the device. Furthermore, we were able to make each project highlight a different function of the device which greatly increased the information we obtained. The three mini projects we decided on were: taking the device apart (highlighting its internal features), measuring the span of local bridges (highlighting the distance measurement capability), and finally measuring the sides and angles of a building on campus (highlighting the bearing capability). Each project provides a procedure report, measured data, calculated results and a description of what was learned. Together, all three 'mini' projects will show a range of information providing each group member with an understanding of basic GPS operation. In addition to the hands on projects each member was responsible for providing one or two extra research facts that weren't previously known.
GPS (Global Positioning System) is a satellite based navigation system. This device uses satellites placed at different vantage points in the earth’s orbit. GPS was developed by the US department of Defense to provide their military with navigation capabilities, but has since then been incorporated into civilian use. When using GPS, the device is able to tell you the distance that you are traveling, the estimated time of travel, and the speed with which you are traveling. GPS is also able to show you alternate routes to where one is going, in case a wrong turn is made in the following of its direction. They can also give you information on service areas as well.
My previous experience with a Global Positioning System (GPS) is only what I know about my TomTom Navigation system I received for Christmas this past year. I know it communicates with satellites to give me a real time map of my location and route of a programmable trip. There are several features you can use such as finding the nearest gas station or museum but you can also program the trip to avoid toll roads or highways so you can make your route match your needs. I believe that GPSs can also give elevations and live traffic updates but I have not experienced either of these features. The military uses GPS all the time so I assume it is a reliable and accurate system. A GPS costs several hundred dollars and are easy to obtain, but I am unsure of what electronic components make up one. Also, I am told my cell phone has a GPS in it to track my signal (I've seen this technology put to use on Law & Order).
I had several experiences with GPS devices before. My first experience was using it to track and find geocache items. You input the coordinates into the device and then you need to find your way to the spot using the compass of the device. My second experience with GPS was using it for turn by turn directions while driving a vehicle. This is very handy and most of the time very accurate. I did have one hiccup and that was that a place we had selected to go had the wrong information, so we ended up in the wrong place. I know that GPS devices use at least 3 satellites to triangulate your position on earth.
GPS stands for Global Positioning System. This device uses signals from various satellites. It can be used on land, water, or air as long as there is a clear path to the satellites. The GPS can be utilized for acquiring bearings, latitude/longitudinal coordinates, elevations, topographic map, distance traveled, and also includes landmarks. I myself own a Garmin GPS for my vehicle. It works for most of the time but the moment a branch is over my car, it loses satellite reception. Other than that minor inconvenience, it is pretty accurate and easy to understand directions. The GPS also has an audio feature to tell the driver when to turn and where.
Before this lab my experience with a GPS was very limited. I have only had usage/experience with GPS car and boating systems. In both instances the GPS was used for directions to get to one location from another, gave me a distance traveled, and where I was during the trip.
My experience with GPS systems before this lab is very minimal. I know that GPS is used in a few jobs as well as consumer products. When I worked at the airport I saw surveyor teams work with GPS to find distances and locations, but did not understand how it worked. Also I am aware that GPS technology is used in tracking devices such as low jacks and animal migration monitors. Some of this tracking technology has been put to common consumer use in TomTom's or other direction giving devices. These can either be installed in cars or used by geocachers. Other than this basic information I am not familiar with how GPS works or its accuracy.
'ALL' this section for what we can find out from text... wikipedia... or online resources...
Assembly and Parts
'KOBINA & SHOYER'
1) In taking the device appart, we were trying to find out the basic components and the types of electronic parts that is found in it. We thought that identifying these components were going to be easy, but it was much difficult than we expected. We expected (basically describe the purpose of your miniproject)
2) Data (include pics)
3) Results (include descriptions) for your section these will be side by side
4) What You Learned (one coherent answer)
|This is a part of the antena that connects to the receiver and transmitter|
|This is a general overview shot of the circuit board removed from the case of the GPS|
|This is an overview shot of the circuit board inside of the GPS case|
|This is a picture showing the USB attachment that allows data to be transeferred from the GPS to a computer|
|This is a shot of the opened memory card holder.|
|This is a picture of the film that puts all of the information from the circuit board onto the screen for us to understand.|
Span of Local Bridges
Start on West side of Market St. and Chestnut St. Bridge. Turn GPS on and wait until device has stabilized, acquiring your coordinates. Press PAGE until screen with coordinates appears. Then press MENU → Reset info → Reset Now. A screen should appear where your time and distance traveled reads zero. Begin walking in a straight line heading east, until reaching the very end of the bridge and recording your distance values. Now head west to the other end of the bridge where you started from. Repeat the process until obtaining four readings for each bridge. Average your results and use this value as the distance of the specified bridge.
Data - Bridge Sketches
This is a copy of the data obtained during our GPS trials. Using the distance traveled we can estimate the lengths of the bridge sections that we were attempting to measure.
From the data we collected we were able to calculate the average distance walked which gives us the best estimate of how long the bridge sections were. For the Market Street Bridge we got an average distance of 561.85 feet and for the Chestnut Street Bridge we got an average distance of 580.8 feet. We then used satellite images to try and determine the actual distance. For the Market Street Bridge we estimated the length to be 444.44 feet and for the Chestnut Street Bridge we estimated the length to be 466.67 feet. Both of these were done by using the bar scale associated with the satellite imaging.
The difference between the average GPS length measurement and the estimated satellite image was about 120 feet for both bridges. This error is huge in relation to both of the measurements, but since we don't have the actual distances we can't be sure or how far off either of the measurements are. The error is the combination of several factors including but not limited too: not being able to walk straight lines because of excessive foot traffic, cloud cover, and precipitation. From this experiment we learned how to operate the GPS device in order to measure distances. We found that distances before 1/10th of a mile are measured in feet while the distances after 1/10th of a mile are measure in miles. This causes problems when you are measuring distances right around that 1/10th of a mile mark like we were.
Length and Angles of Building
We wanted to see if we could correctly determine the length and angles of a popular building on campus. It was decided that Korman was a perfect opportunity due to it's relatively level elevation and lack of external gates. Our first step was to figure out how to operate the GPS device. This took us about 10 - 20 minutes as we looked through the manual for operation buttons. We discovered that by pressing the "page" button twice a screen would appear that would allow us to measure distances. Using this screen we selected a start point and then paced the distance of each side. At the end of the side we recorded the measurement and reset the data for the next side. Once we had the length of each side we could start to measure the bearing angle of each side. This was done from a different screen on the GPS device again using the page command. To find the bearing angle you must be traveling therefore we would again walk along each side of Korman. After we had each of the measurements we could use our surveying studies from class to determine if our data was accurate.
Data - Field Measurements
This is a copy of the data obtained during our GPS trials. Using the bearing angles of each side we can determine the interior angles of the Korman building. Applying n-2*(180) equation we can see that the interior angles must add up to 1080 degrees. After we have confirmed accurate angles we can use the latitude and departure theory to determine if our length measurements are correct. Below is the excel sheet of calculations as well as the final corrected results.
Results - Excel Calculations - Adjusted Measurements
As you can see from the excel file the measured interior angles of Korman added up to exactly 1080 degrees. This means that our angles do form the octagonal shape of the building. Our next step was to check the side lengths. We calculated the latitude and departure of each side and found that the GPS measurements were very flawed. They showed that the latitude was off by 100 feet and the departure was off by 50 feet! Considering the relatively small size of the building this flaw is enormous. However, we still went through the compass correction formula and adjusted the side lengths to close the traverse. The final values of angles and length are shown in the adjusted measurements file.
As stated previously we found that the latitude and departure of our measurements were quite erred. We think that this may be due to the fact that we were measuring small distances. When the GPS device is used in cars or travel it is usually over a distance of miles, this means that an error of 50 ft will have less effect on results. However, since our project required the measurement of 50 ft sides this kind of error could potentially double the correct value. The angles on the other hand added up to 1080 as expected. Although we think this may be coincidence since some geometrically corresponding angles are not the same. Also, we found that unless you read the GPS manual it is very difficult to figure out how to measure things. The "page" button is almost misleading in that instead of making a new page of data it cycles through the functions of the device. To reset data you must hit "menu" then "reset data" then select the data you wish to reset before pressing "enter" one last time. We felt that this was very monotonous and time consuming especially since we had to do this after each of the 8 sides. Altogether the 'mini' lab taught us the general operations of the device as well as demonstrated the variability of its results.
what we learned... what we already knew... what we can conclude from our miniprojects