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Definition
the science of the measurement and mapping of the earthâ€™s surface 


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Definition
A survey of a large area of land in which corrections are made to account for the curvature of the earth 


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Definition
world geodetic system 1984  latitude, longitude, and ellipsoid height (X = Greenwich meridian) 


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Definition
the real earth; equipotential surface (equal gravity) that best equates to Mean Sea Level; very complicated surface; can be sensed by instruments 


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Definition
simple geometric surface; can't be sensed by instruments; WGS84 uses best mean fit to the Earth 


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Definition
The height difference between the ellipsoid and the geoid 


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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 


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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) 


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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 


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Definition
A set of controlpoints to realize a Reference System 


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Definition
traditional Term for Reference System 


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Definition
type of projection that results from projecting a spherical surface onto a plane 


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Definition
modified cylindrical projections with all longitudes parallel, and latitudes increasing in size farther North or South 


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Definition
cylindrical projection that intersects globe at two areas; used in U.S. for states that run norhtsouth 


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Definition
has a cone for each parallel; very accurate northsouth; accuracy distorted eastwest 


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Definition
based on a table of coordinates; projection distorts shape, area, scale, and distance in an attempt to balance the errors of projection properties 


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Definition
secard conic (cone intersects globe at two areas); used for states that are long eastwest 


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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!) 


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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 onetenth 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/cutoff 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
EGNOSeuropean MSASasia GLONASSrussian GalileoEuropean 

