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 and knowledge of a GPS was very limited. I knew that a GPS worked as a tracking system with the ability to locate where a person is at anytime. I have learned this because of my personal experience with a GPS. I have used a GPS in a car when finding directions and location of a destination. The GPS gave me exact distances of where I needed to go along with informing me of my location throughout. Another time I used a GPS was in a boat where I was able to find out distances from the shore and the depth to the ocean bottom below.
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.
The GPS satellite navigation system was designed by the United States Department of Defense (DOD) for the military to accurately determine the positions of vehicles, personnel, submarines, etc. Civilian usage was limited at the time. Early navigation systems were tested by the U.S. Air Force and Navy including TRANSIT, TIMATION, and 621B, from 1973- 1979. The DOD then launched NAVSTAR (later known as GPS), strictly for the military, in 1978 operating under eleven satellites orbiting the earth. This system did not become fully operational until 1995 when a full constellation of 24 satellites were in orbit. The GPS evolved over time becoming more accurate and available to the public thanks to the authorization of President Reagan in 1983. Degradations were applied to the signal being received by civilian GPS receivers known as Selective Availability (SA). SA was active until the Clinton Administration where in 1996, President Clinton gave an executive order for the removal of Selective Availability. As of the 20th of March, 2004, the 50th GPS satellite was launched into space. The Global Positioning System utilizes a minimum of four satellites, acquiring velocity, position, and time. The GPS acts as the receiver, receiving three effective signals from a set of satellites that act as the transmitters and a signal from a fourth satellite which acts as a correcting factor. At least four satellites are available to the system at any given time and location to compensate for the time delay it takes for the signal to reach the GPS receiver. This pulsed timing system uses the product of the difference of time and the speed of light to determine the range of the satellite. For more details, visit http://en.wikipedia.org/wiki/Global_Positioning_System
1.) The satellites we use for GPS were originally launched for military purposes by NavStar.
2.) The first GPS satellite was launched in 1978.
3.) The current system is using second generation GPS satellites, type BLOCK II. The first BLOCK II satellite was launched in 1989.
4.) The GPS system was fully operational on April 27, 1995.
5.) The satellites orbit at 20,000 km (12,500 mi) high and circle the earth in 12 hours.
6.) The developmental cost for a satellite is estimated at $12 billion.
7.) Russia has a navigation system called GLONASS, similar to the United States’ GPS. This also became operational in 1995.
8.) Currently, the U.S. has not produced any laws controlling the information received from GPS units. This may be a problem since the system has the capability of invading one’s privacy when in the wrong hands.
9.) Some satellites that the GPS uses have been operational for 10 years, however, the expected average lifespan is about seven and a half years.
10.) Scientists collaborated with the military during hurricane Katrina, flying into the eye of the storm, dropping GPS-enabled dropsondes to monitor and predict the speed, magnitude and direction of the storm. These dropsondes combine GPS receivers with pressure, temperature, and humidity sensors to capture atmospheric profiles and thermodynamic data. While the dropsonde descends on a parachute, in-air scientists receive its data via RF transmitters to review, quality-assure, and forward to hurricane forecasters
I – Garment has produced a state-of-the-art "smartsuit" that utilizes GPS and Wi-fi. It will be used to monitor a rescue workers position and his/her vital signs via sensors strategically located on the suit during disaster relief. The European Space Agencyhas already incorporated this life-saver into their equipment list. The following are the major issues being addressed by this design.
1. The unavailability of communications channels
2. The lack of information as to the exact location of safety personnel during emergency efforts.
3. The inability to send graphical information (maps, satellite data) during an emergency that
could help emergency teams to manage dangerous situations better.
Farmers are integrating hundreds of years of traditional knowledge with modern technology to manage their crops more efficiently via tractor-mounted GPS receivers to calculate and record its position. This information helps determine how much fertilizer, weed control, and water is needed in various locations of the field. Additional soil analysis combined with market information about predicted crop prices helps farmers decide the best crop rotation. In precision agriculture, farmers combine GPS data with other information such as soil samples, moisture content, weed density, and crop yield in a computer spreadsheet.
Assembly and Parts
During dissembling we experienced minimal difficulty separating the GPS into its different components. The GPS splits in almost two equal halves with a main circuit board sandwiched within. We had to take out a total of nine screws to completely dissemble it, and that only took about three minutes. In general, taking it apart was very easy. While taking apart the system our goal was to try and find out the basic components and the types of electronic parts inside. After taking pictures and identifying the parts we reassembled the device in working order. Photo's and descriptions of internal components are provided below:
Pictures and Description of Parts
|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. The big square shaped yellow component located atop is the transmitter receiver module. This is what makes communications with the satellites possible.Other GPS devices have their transmitter and receiver modules seperated, but this device has its own put together.|
|This is an overview shot of the circuit board inside of the GPS case. About twenty-four integrated circuits (ICs) were counted from it.|
|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. The GPS has an internal memory of it's own. The additional memory card for the user to save more map informations for easy access.|
|This is a picture of the film that puts all of the information from the circuit board onto the screen for us to understand.|
|12mm magnetic sound transducer, 3.6V, SMT mount.The function of this is to generate either a single continuous sound or intermittent tones to alert the GPS user regarding some particular information or alerts.|
After taking the GPS apart we were able to better understand the electrical components required for a device of GPS's caliber to run properly. Initially we thought that identifying these components would be easy, but it turned out to be a much more difficult task than we expected. Identifying important parts such as the receiver and transmitter components separately was difficult because this GPS system had them together in one module. After which we realized that there are two types of transmitter receiver modules used in making a GPS system. Another aspect we found was the numerous amount of integrated circuits. We did not expect there would be such a large amount of ICs working together in such a small device. It was really amazing to see just how much is needed for a GPS to operate. It made us wonder the amount of time, effort, and planning it takes to put together one of these devices because each component had to be in an exact spot or the device would not function properly.
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.
Since the beginning of this project it has been our goal to understand GPS and its functions through hands on learning. Creating three mini projects has given each student the opportunity to work directly with the device. With this hands on experience paired with background research we all agree that this project has been an excellent source of information. When we look back on our initial understanding of GPS we realize how much knowledge we have gained both in a general sense and its direct functions. Most of us initially believed it only had transportation importance; however after applying it to real life projects we understand it can be used for a lot more than that. Below are some final conclusions about the device that we have developed:
1.) We feel the GPS device should not be used for short length measurements. During our measurements we found it very inaccurate due to having less readings for short distances. If we had been measuring a large distance the system would take more measurements from satellites which would have greatly increased its accuracy.
2.) Readings in cloud covered areas are more erred. This happens because of interference between the device and the corresponding satellites.
3.) The GPS is not very efficient at taking many measurements quickly. Before each measurement we had to reset the device, this process required scrolling through multiple screens. After we got to the right screen we had to select the values we wanted to reset, press ENTER and return back to the original screen.
4.) The bearing angles we measured were more accurate than other readings. We noticed that a bearing direction could only be taken while we were in motion with the GPS. This means that you couldn't just stand in one spot and take the reading. As we moved with the GPS system we found that it continuously corrected our bearing and we were able to take an average of these measurements. This average means a more accurate measurement than if we had just stood there.
5.) The battery life of the GPS is very good. We were able to do a variety of things without having to recharge the battery. This included: initial set up, all three mini projects, learning the functions, and an entire day when the device was accidentally left on. We felt this was very practical because if you're in the wilderness using this device you won't be able to recharge often.
6.) The GPS device is much more complex than anticipated. We knew from the initial installation of topographic maps that the interior had to contain some computer components. We also knew that the device had to have some kind of transmitter and receiver. However, we did not know how complex this system was until we opened it up. We discovered several circuit boards, computer hook ups, image converter, memory storage, antenna and multiple smaller segments we were unable to identify without further knowledge and research of electronics.