Data input Flashcards
Lecture 9
What are spatial data sources?
- Spatial data is one of the most important components of a GIS.
- Unfortunately, spatial data is often very expensive.
- In the case that it is cheap or open source the data are often of lower quality.
Vector data:
Shapefiles might be lacking topological relationships
Comprise digitizing errors + Attribute errors too
Raster data:
Coarse scale vs fine scale (i.e. spatial resolution)
Temporal resolution (landscapes change over time)
what kind of source can the data be?
Primary - not processed = raw data
Secondary - processed data / from another party.
What is data encoding? (digitising)
converting data from no -digital to digial format.
What are the three steps to data encoding process?
- Geocoding - capturing co-ordinates for the observation.
- Add attributes - what do the data points represent?
- Quality assurances - checking that data has been captured accurately and precisely.
What are data input methods?
- Data encoding = hard copy (analogue) maps and tables
- Data encoding also known as key coding
- Can be used for attribute data only
- Many methods of data encoding:
- Digitizing (Manual = Tablet & HUD OR automatic stream mode)
- Keyboard, COGO – typing from keyboard (mainly attributes; occasionally co-ordinates
- Scanning
- Direct file transfer, file conversion
- Remote sensing images
What is manual digitizing?
Keyboard entry
Drawing - paint mode, node captured per click
stream mode - modes captured at a set rate per time unit.
What is Heads up digitizing?
What is scanning?
and the advantages and disadvantages.
- Automatic digitizing = Conversion of paper (analogue) map to digital format.
- Results in gridded data or vector
Disadvantage: Need lots of cleaning after scanning is completed; especially removal of non-target features.
Advantage: cost-effective for capturing very large volumes of data
- Quality – depends on resolution of the scanner
What is GPS?
**A system of earth-orbiting satellites that provide location (in lat/long
coordinates or equivalent) and time information in all weather conditions, anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. **
- Primary vector data.
- Derives spatial coordinates of spatial feature/phenomena using a processes triangulation
- Achieves accurate positional readings through triangulation of signals from at least 3 satellites
- Publicly available GPS Satellite system (NAVSTAR) developed by the US military.
What are GPS segments?
Space segment
Control
User segment
What is space segment?
- Constellation of 24 (upgraded to ~32) Satellites or “Space Vehicles” (SV) ➔ Arranged in six equally spaced orbital planes
- Orbits @ Altitude of 20 183km.
Satellite that sends a radiowave /pulse that is sent to the control segment.
What is the control?
Monitor stations
that track and monitor, update and synchronise SV’s.
What is the user segment?
GPS receivers
Apps - google maps
Software
What are the basic processes of capturing the approximate location? (never exactly)
Triangulation:
- Receiver calculates distance to available satellites using the travel time of radio signals
- Through triangulation, receiver identifies it’s own position on the earth’s surface
- We’re using the word “triangulation” very loosely here because it’s a word most people can understand, but purists would not call what GPS does “triangulation” because no angles are involved. It’s really “trilateration.”
Examples of GNSS
- GLONASS (Global Navigation Satellite System) – Russian.
- Galileo positioning system – EU & ESA.
- COMPASS navigation system (aka Beidou-2) – China.
- IRNSS (Indian Regional Navigational Satellite System) - India.
