GPS Bao Dinh Nguyen [email_address] 15 Nov 2008

Agenda GPS – how it works Vietnam – what are Vietnam’s needs

GPS – how it works

Vietnam – what are Vietnam’s needs

Definition GPS – Global Positioning System Global: Available everywhere (including Vietnam) Positioning: Gives precise position in space System: Hardware + Software. Multiple satellites transmitting clock and orbit data to user receiver, which computes position using mathematical algorithms NOT to be confused with GPRS (General Packet Radio Service), related to cell phone telephone technology

GPS – Global Positioning System

Global: Available everywhere (including Vietnam)

Positioning: Gives precise position in space

System: Hardware + Software. Multiple satellites transmitting clock and orbit data to user receiver, which computes position using mathematical algorithms

NOT to be confused with GPRS (General Packet Radio Service), related to cell phone telephone technology

What is GPS? GPS is a tool, like the cellular telephone. GPS is used for finding position and for routing. Vietnam currently does not use this tool because Precisely surveyed maps are not available for portability Wide uses have not been identified (cost has not yet been justified) Cultural inexperience with maps, directions, large distances, and precision

GPS is a tool, like the cellular telephone. GPS is used for finding position and for routing.

Vietnam currently does not use this tool because

Precisely surveyed maps are not available for portability

Wide uses have not been identified (cost has not yet been justified)

Cultural inexperience with maps, directions, large distances, and precision

GPS Signal From any location on the earth, a receiver can see between 4 and 12+ satellites in space. The signal can be obstructed by trees, buildings, and mountains. It can be degraded by heavy cloud cover and high ionospheric activity. (x 1 , y 1 , z 1 , t 1 ) (x 2 , y 2 , z 2 , t 2 ) (x 3 , y 3 , z 3 , t 3 ) (x 4 , y 4 , z 4 , t 4 )

From any location on the earth, a receiver can see between 4 and 12+ satellites in space. The signal can be obstructed by trees, buildings, and mountains. It can be degraded by heavy cloud cover and high ionospheric activity.

GPS Satellites (24+ in US system) Originally launched in 1980s 6 medium earth orbits (20200 km altitude) of 4 satellites each, plus spares Each satellite orbits the earth twice in 24 hour period Has atomic clock that keeps time to the nanosecond. Transmits satellite position, velocity, and time in multiple frequencies, 2 of which are unencrypted.

Originally launched in 1980s

6 medium earth orbits (20200 km altitude) of 4 satellites each, plus spares

Each satellite orbits the earth twice in 24 hour period

Has atomic clock that keeps time to the nanosecond.

Transmits satellite position, velocity, and time in multiple frequencies, 2 of which are unencrypted.

GPS Signal Travels at the speed of light. Affected by hardware in transmission and reception. Affected by environment, and altered by earth rotation (doppler) and relativity May not reach receiver in straight line (bounce off walls, go through ionosphere, etc)

Travels at the speed of light.

Affected by hardware in transmission and reception.

Affected by environment, and altered by earth rotation (doppler) and relativity

May not reach receiver in straight line (bounce off walls, go through ionosphere, etc)

User receiver A user receiver can be a portable device, attached to an automobile/boat/airplane, or reside on top of a building. Sophisticated receivers are generally used for research, surveying, or for landing capability. Receives multiple frequencies Has atomic clock Has fast cpu Inexpensive receivers are used by hobbyists or for automotive routing. Receives single frequency Has cheap clock Has basic cpu

A user receiver can be a portable device, attached to an automobile/boat/airplane, or reside on top of a building.

Sophisticated receivers are generally used for research, surveying, or for landing capability.

Receives multiple frequencies

Has atomic clock

Has fast cpu

Inexpensive receivers are used by hobbyists or for automotive routing.

Receives single frequency

Has cheap clock

Has basic cpu

Basic equation Satellite transmits (x 1 , y 1 , z 1 , t 1 ) at time t 1 . User receives (x 1 , y 1 , z 1 , t 1 ) at time t. Since signal travels at the speed of light, c, then the distance between the satellite and the receiver is (t – t 1 )*c So the first equation in our system is (x 1 , y 1 , z 1 , t 1 ) (x, y, z, t)

Satellite transmits (x 1 , y 1 , z 1 , t 1 ) at time t 1 .

User receives (x 1 , y 1 , z 1 , t 1 ) at time t.

Since signal travels at the speed of light, c, then the distance between the satellite and the receiver is (t – t 1 )*c

So the first equation in our system is

User Solution 4 unknowns (x, y, z, t). At least 4 equations (satellites) are needed to solve. Solution converts Earth Centered Earth Fixed position coordinates to Latitude/Longitude position plus elevation. Time solution is also included.

4 unknowns (x, y, z, t). At least 4 equations (satellites) are needed to solve.

Solution converts Earth Centered Earth Fixed position coordinates to Latitude/Longitude position plus elevation. Time solution is also included.

Errors With all physical systems, errors increase with the level of complexity. Errors include, but not limited to Satellite position/velocity errors Satellite clock errors Transmission errors Environmental effects leading to errors (multipath, noise) Receiver errors Errors all add up to give imprecise user solution. In lateral position, errors can be as high as 10m. In the vertical position, errors can be over 100m, making it unsuitable for landing aircraft. Systems exist to correct for errors.

With all physical systems, errors increase with the level of complexity.

Errors include, but not limited to

Satellite position/velocity errors

Satellite clock errors

Transmission errors

Environmental effects leading to errors (multipath, noise)

Receiver errors

Errors all add up to give imprecise user solution. In lateral position, errors can be as high as 10m. In the vertical position, errors can be over 100m, making it unsuitable for landing aircraft.

Systems exist to correct for errors.

Primary uses Civilian – Used in farming, road navigation, geocaching, saving points of interest, etc. Non-military government – Used in civilian airspace navigation, geographic based research, surveying for roads/borders/topography, etc. Military – Used in aircraft, missiles (Bao D Nguyen doesn’t do weapons)

Civilian – Used in farming, road navigation, geocaching, saving points of interest, etc.

Non-military government – Used in civilian airspace navigation, geographic based research, surveying for roads/borders/topography, etc.

Military – Used in aircraft, missiles (Bao D Nguyen doesn’t do weapons)

Vietnam Probably already used by government of Vietnam for map and border surveying. Used by hobbyists to save points of interest, or to get a layout of big and unfamiliar areas, such as the countryside, or the city. Used for basic air navigation, to know latitude and longitude. NOT SAFE for landing, due to errors in vertical position. (Systems exist to correct for errors)

Probably already used by government of Vietnam for map and border surveying.

Used by hobbyists to save points of interest, or to get a layout of big and unfamiliar areas, such as the countryside, or the city.

Used for basic air navigation, to know latitude and longitude. NOT SAFE for landing, due to errors in vertical position. (Systems exist to correct for errors)

Vietnam Maps Currently, Vietnam does not have detailed maps in electronic form to upload to portable GPS device. (As far as I know)

Currently, Vietnam does not have detailed maps in electronic form to upload to portable GPS device. (As far as I know)

Detailed Maps Detailed street level maps are used extensively in the US, Europe, Japan, Korea, etc.. In SE Asia, maps exist for Singapore, Malaysia, Thailand, Indonesia, Hong Kong, Macau In the near future, Vietnam should have detailed street level maps.

Detailed street level maps are used extensively in the US, Europe, Japan, Korea, etc.. In SE Asia, maps exist for Singapore, Malaysia, Thailand, Indonesia, Hong Kong, Macau

In the near future, Vietnam should have detailed street level maps.

Topology Topographic maps may be useful for farming, etc.

Topographic maps may be useful for farming, etc.

Street Level Surveying Maps are best surveyed using moving receivers. Latitude/Longitude is saved, in addition to precise elevation. This is not practical in Vietnam due to cost and the difficulty in getting the equipment through traffic and construction.

Maps are best surveyed using moving receivers. Latitude/Longitude is saved, in addition to precise elevation.

This is not practical in Vietnam due to cost and the difficulty in getting the equipment through traffic and construction.

Google Mapmaker (http://www.google.com/mapmaker) Google has a mapmaker tool that allows users to identify streets and locations. Problem is that these maps may soon be offered for online use only, since they remain the property of google. May be a project for someone to get the same sort of street level maps for portable use.

Google has a mapmaker tool that allows users to identify streets and locations.

Problem is that these maps may soon be offered for online use only, since they remain the property of google.

May be a project for someone to get the same sort of street level maps for portable use.