a constellation of 24 satellites (21 +3 operating spares)
medium oribit of 12,552 miles
What are the components of the control segment of GIS?
they track the location and health of each satellite
health refers to the errors and clock time on each satellites
there are 11 stations that can be seen by at least 2 satellites
Explain the user segment of GIS.
The GPS receivers that are tuned to the radio frequencies from the satellites
Accuracy for regular GPS is 3 meters
Selective Availability is the intentional degredation of GPS signals
Explain how GPS works.
There are at least 3 satellites above you
A GPS receiver and satellite clocks are precisely and continually synchronized , but there can be errors if your GPS receiver's clock is 0.1 second fast
What are the satellite inaccuracies for GPS?
orbital bias
satellite dock bias
What are signal inaccuracies of GPS?
Troposhperic effects
Ionospheric bias
This occurs when the GPS signal bounces before it reaches the antenna on the GPS receiver
Multipath Error
What are the characteristics of Differential GPS?
requires 2 receivers (mobile and base station
corrects its GPS positions using the base station info
Errors can be within one meter
Explain the characteristics of Wide Area Augmentation System (WAAS).
THey measure small variations in GPS satellies' signals
For commercial aviation
use ground-based wide area and reference stations & geostationary WAAS satellites
How are Triangulated Irregular Networks different from DEM models?
base on triangle grid (not pixel grid)
different sized triangles (not equal)
WHat is a centroid?
THe balance point or center of gravity of an AREA
WHat are the two sets needed for geocoding?
Address Table
Reference DAtabase
What is the formula for the distance theorem?
D= the square root of (X_{2}-X_{1})^{2} + (Y_{2 }-Y_{1})^{2}
How do you calculate physical distance?
you accumulate each straight segment
WHat are some errors to measuring physical distance?
Slope Errors-mountain
Network Distance- physical distance is less than highway distance
Centroid Representation-where exactly are you measuring to?
Hard Copy
Seasonal Variation
What are Isochrones?
Lines of equal time distance
What are two methods of measuring area in GIS?
Grid Cell Counting Method
Strip Method
How do you measure the shape index?
divide the intersection by the unit
if the distance is close to zero, then they are very close to each other
What is the most common function distance
travel times
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