Term
| What does GNSS stand for? |
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Definition
| Global Navigation Satellite System |
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Term
| What are the 3 segments of GNSS? |
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Definition
1. Satellite
2. Control
3. User |
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Term
| What is currently the only working system? |
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Definition
| NAVSTAR (Military System) |
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Term
| What does NAVSTAR consist of? |
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Definition
1. 24 satellites orbiting at 20,000 km
2. 2 orbits daily
3. 6 offset orbital planes
4. 5-8 satellites should be visible at all times from any one.
*Clear Point – buildings or forest can affect signal |
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Term
| Where is the Control of NAVSTAR located? What does the Master Control Station do? |
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Definition
1.Colorado
2. The Master Control Station checks on each satellite and relays information to them. |
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Term
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Definition
| yourself, the person holding the GPS. |
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Term
| What is GLONASS? is it up and running? |
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Definition
| Russian System, currently down for upgrades |
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Term
| Define the system "Galileo" |
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Definition
1. European Union System
2. Scheduled for operation in 2014
3. 30 satellites with better high latitude coverage
4. 23,600 km altitude
5. planned to be compatible with NAVSTAR |
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Term
| What is Broadcast Signals? |
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Definition
GPS satellites all broadcast L1 and L2 signals
1. L1
-Actually a set of signals (carrier signal) separated and read by your receiver
2. Includes both Coarse Acquisition (C/A) and P (Private) signals.
3.Receiver can recognize number of satellite, its location, the exact time (atomic clock on each satellite), and where all satellites are due to be for the next few days. Satellite actually sends a signal to see how long it takes to get to receiver. |
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Term
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Definition
| Certain conditions in earth’s ionosphere and atmosphere may slow the signal and make range inaccurate – Closely bunched satellites won’t find location as well as more spread out satellites – trees or obstacles may also make range inaccurate |
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Term
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Definition
| Use a base station to remove error from raw data. makes correction based on GPS citation a person has made to a station. |
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Term
| Real-time Differential Correction |
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Definition
| If you are near a broadcasting base station and you have a real-time capable GPS receiver and antenna you can get immediate corrections for your gps readings which are transmitted from the base station. This network of base stations in the US is called CORS (Continuous Operation Reference Stations). These stations are mostly located near the coasts and major waterways of the US because they were originally for shipping navigation. |
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Term
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Definition
Wide Area Augmentation System
-broadcast by FAA for air navigation – ground-based stations constantly read GPS error to estimate locations within 7 meters – good enough for airplanes |
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Term
| What Datum was GPS set up on? |
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Definition
| WGS84, which may make some error based on data in NAD83 |
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Term
| What are some examples of Hardcopy Data Sources? |
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Definition
1.Old Maps (Pre-1960 virtually all maps were hardcopy, hand drafted)
2.More recent maps on mylar
3.Manually measured survey data and surveyors notes
4.Legal records
5.Coordinate lists
6.Photographs
7.Tables of data |
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Term
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Definition
| computer-compatible format, often in compressed format on the Internet |
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Term
| why si map design still important in GIS? |
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Definition
| conveys information efficiently and effectively |
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Term
| What are the Map Components (there is 8 of them)? |
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Definition
1. Neatline frames all the elements of a map
2. Portrait vs Landscape – let the shape of your basemap lead you
3. Insets may contain a finder map or other relevant information
4. Scalebar – shows linear scale graphically – scale is ratio of map distance to real distance
5. Legend – key to the map’s value scheme
6. Titles – you know what a title is
7. North Arrow – particularly important when north is not at top of map
8. Graticule – latitude and longitude lines |
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Term
| What are the Map Types? (there are 5 of them) |
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Definition
1. Feature map – just symbols and nominal data, e.g. road maps, topo maps
2. Choropleth map – quantitative data for areas, usually with shading
3. Dot-density map – dots within areas represent quantitative data, note: placement of dots is usually
4.random – dots don’t show concentrations within areas
5. Isopleth map – show lines of equal value, e.g. rainfall, elevation, air pressure, etc. |
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Term
| What are soem components of Map Scale? |
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Definition
linear ratio between map and reality
-1:24000 means 1 unit on the map is equal to 24000 units in reality – do not change units!
-Large-scale vs. small-scale in GIS runs against logic, e.g 1:2000 is a large-scale map b/c it is near to reality – 1:36000000, typical for a globe, is a small scale b/c it is so much smaller than reality |
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Term
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Definition
Unavoidable approximation of real features on a map, esp due to scale
-Fused – multiple features grouped into one
-Simplified – boundary or shape detail lost or rounded off
-Displaced – features offset to prevent overlap
-Omitted – small features left off map
-Exaggerated – standard symbol sizes beyond scale, e.g. road widths |
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Term
| What is Digitizing? what are its components? |
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Definition
coordinates from a map, image or other source, converted into digital format in GIS
1.Digitizing on a tablet with a live puck and a dense electric network in the tablet
2.Obvious points with known coordinates used as control points to situate map digitally before beginning to digitize specific features
3.On-screen digitizing, also “heads-up” digitizing with a digital image as backdrop
4.Done using a mouse onscreen
5. Tiny digitizing errors translate into big inaccuracies, esp at small scales, e.g. 1 mm error at 1:100000 scale means a 328 ft error in reality
6. On-screen digitizing usually more accurate than tablet digitizing due to lack of precision in digitizing tablets
7. Point digitizing – one point at a time / Stream digitizing
8. Points are recorded as you slide mouse
9. Nodes – end of digitized line / Vertices – points within lines |
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Term
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Definition
Optical scanner creates raster image of existing hardcopy map
1. Works well for very clean maps
2. Folded, wrinkled maps, or maps with many layers not good for scanning as many spurious points show up |
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Term
| what components are in Editing? |
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Definition
Rubbersheeting-is a technique where two maps are combined, but they do not match perfectly – choose better map and match features on less reliable map to locations on the more reliable map – GIS will pull and tug less reliable map into correct locations, as if the map were rubber sheet
Edge Matching- is same as rubbersheeting, but just along the edge of adjacent maps in a mosaic, matching linear features like roads or streams |
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