Term
|
Definition
| the science of the measurement and mapping of the earth’s surface |
|
|
Term
|
Definition
| A survey of a large area of land in which corrections are made to account for the curvature of the earth |
|
|
Term
|
Definition
| world geodetic system 1984 - latitude, longitude, and ellipsoid height (X = Greenwich meridian) |
|
|
Term
|
Definition
| the real earth; equipotential surface (equal gravity) that best equates to Mean Sea Level; very complicated surface; can be sensed by instruments |
|
|
Term
|
Definition
| simple geometric surface; can't be sensed by instruments; WGS84 uses best mean fit to the Earth |
|
|
Term
|
Definition
| The height difference between the ellipsoid and the geoid |
|
|
Term
|
Definition
| a system of intersecting lines, such as the grid of a map, on which part or all of the globe or another spherical surface is represented as a plane surface |
|
|
Term
|
Definition
| Shape, size, position and orientation of a (mathematical) Reference Surface, (eg. Sphere or Sheroid). It normally is defined in a superior, geocentric three dimensional coordinate system (for example WGS84) |
|
|
Term
|
Definition
| mathematically (eg. Sphere or Sheroid) or physically (Geoid) defined surface to approximate the shape of the earth for referencing the horizontal and/or vertical position |
|
|
Term
|
Definition
| A set of controlpoints to realize a Reference System |
|
|
Term
|
Definition
| traditional Term for Reference System |
|
|
Term
|
Definition
| type of projection that results from projecting a spherical surface onto a plane |
|
|
Term
|
Definition
| modified cylindrical projections with all longitudes parallel, and latitudes increasing in size farther North or South |
|
|
Term
|
Definition
| cylindrical projection that intersects globe at two areas; used in U.S. for states that run norht-south |
|
|
Term
|
Definition
| has a cone for each parallel; very accurate north-south; accuracy distorted east-west |
|
|
Term
|
Definition
| based on a table of coordinates; projection distorts shape, area, scale, and distance in an attempt to balance the errors of projection properties |
|
|
Term
|
Definition
| secard conic (cone intersects globe at two areas); used for states that are long east-west |
|
|
Term
|
Definition
| the Ratio of a distance on the grid projection to the corresponding distance on the ellipse |
|
|
Term
|
Definition
| used to scale ground distances to grid distances, or vice versa; a product of both the Elevation Scale Factor and the Projection Scale Factor |
|
|
Term
|
Definition
| space (satellites); control (ground control stations); user (us!) |
|
|
Term
|
Definition
| satellites that continuously broadcast position and time in circular orbit around Earth; contain receivers and transmitters |
|
|
Term
|
Definition
| tracks satellites & checks & corrects orbits and clocks |
|
|
Term
|
Definition
| NAVigation Satellite Time And Ranging |
|
|
Term
|
Definition
1. Space
2. Control
3. User |
|
|
Term
| Why is GPS better than traditional surveying... |
|
Definition
Weather independent
Does not require line of sight
Gives high geodetic accuracy
Can be operated day and night
In general it is quicker and requires less manpower |
|
|
Term
|
Definition
| Time Taken x Speed of Light |
|
|
Term
| Example of error for one-tenth of a second off.. |
|
Definition
| 1/10 second error = 30,000 Km error |
|
|
Term
| How GPS works in five steps: |
|
Definition
1. The basis of GPS is "triangulation" from satellites.
2. To "triangulate," a GPS receiver measures distance using the travel time of radio signals.
3. To measure travel time, GPS needs very accurate timing.
4. Along with distance, you need to know exactly where the satellites are in space.
5. Finally you must correct for any delays the signal experiences as it travels through the atmosphere. You must also correct for the clock differences between the GPS receiver and the satellites. |
|
|
Term
| Number of satellites required for point positioning: |
|
Definition
3 to determine longitude and latitude
4 to determine height |
|
|
Term
|
Definition
| three spheres in 3D space intersect at no more than two points; one is discarded since it is not on the geoid at all |
|
|
Term
|
Definition
| uses the known locations of two or more reference points, and the measured distance between the subject and each reference point; uses geometry of triangles; 3 ref. points needed for trilateration alone |
|
|
Term
| Measuring distance to a satellite |
|
Definition
distance = rate x time
satellite transmitter sends a number of unique signals that repeat every millisecond
GPS measures how long it takes to recieve signals from satellite transmitter
time delay in signal transfer determines distance |
|
|
Term
| Selective Availability (SA) |
|
Definition
| dep. of defense can degrade signal over specific areas of the world during conflict; disabled May 2000 |
|
|
Term
|
Definition
locations or landmarks worth recording and storing in your GPS. These are locations you may later want to return to.
They may be check points on a route or significant ground features. (e.g., camp, the truck, a fork in a trail, or a favorite fishing spot). |
|
|
Term
|
Definition
| a series of waypoints entered in the order that you want to navigate them |
|
|
Term
|
Definition
| timing; satellites drift from their predicted orbits; waves travel through a number of Earth's layers and can be delayed; signal may be reflected from objects like buildings; mask angle/cut-off elevation if satellites have low angles |
|
|
Term
| How to minimize GPS errors |
|
Definition
differential GPS - uses reference point with known coordinate
eliminates errors in the satellite and receiver clocks
minimizes atmospheric delays
Accuracy 5 mm - 5 m |
|
|
Term
|
Definition
geometrical dilution of precision
includes latitude, long, height, and time |
|
|
Term
|
Definition
positional dilution of precision
includes lat, lon, and height |
|
|
Term
|
Definition
horizonal dilution of precision
includes lat and lon |
|
|
Term
|
Definition
vertical dilution of precision
includes only height |
|
|
Term
|
Definition
global navigation satellite system
EGNOS-european
MSAS-asia
GLONASS-russian
Galileo-European |
|
|
