Summer Exam Flashcards
Geomatics definition
Modern scientific term referring to inter grated approach of measurement, analysis, management and storage and display of descriptions and location of earth based data- School of geomatics university of NSW.
Essentially application of GPS GIS and remote sensing
Remote sensing definition
Barrel and Curtis 1999- sciences of observation from a distance- VAGUE
Lillesland et al 2004- science and art of obtaining info about an object/ area through analysis of data acquired by device not in (physical) contact with object/ area under investigation.
GPS definition
System of orbiting satellites used for navigation purposes and capable of giving highly accurate geographic co-ordinates using hand held receivers- Heywood et al 2002
GIS definition
ESRI- an organised collection of computer hardware, software data and personally designed to efficiency store, update, manipulate and display all forms of geographically referenced information
āSā in GIS
System- means people, software, hardware and data.
Science- Issues surrounding use of GIS- data quality and interpretation.
Studies- legal and ethical use of GI
Service- NEWEST IDEA- GI to use Internet
GIS output
Maps, tables, graphs, images, 3D fly throughs.
Map output is perhaps most important form of spatial data representation. - layout important as to convey all relevant information.
Tackling a problem using geomatics example
What is the question? Is it getting wetter in Cumbria
What data are required? Rainfall data in time and space
How do I get data? How can data manipulated to answer question? Rainfall data- reformat it, map it- colour code accordingly then use it to answer question.
GPs systems
See sheet 2 for diagram.
Set of satellites which allow receivers to determine exact location 24 hours a day.
2 current systems: NAVSTAR (USA) GLONASS (Russia), European and Chinese systems under construction.
NAVSTAR- most commonly used: consists of 24 satellites each has 12 hour orbit. Pass over control systems so their orbits can be monitored and positions precisely identified.
GPS data transmission
- Radio signals are transmitted to receiver from each satellite.
- Time delay measured between transmission and receiving signal.
- Time delay, distance between receiver and satellite calculated from this.
- Signal from 3 or more satellites, triangulation can be calculated 2D location of receiver.
- 4 or more satellites (often more found but some ignored) , altitude of receiver can be calculated. Further apart satellites= more accurate position.
Dilution of precision of GPS
No GPS is 100% accurate, generally +/- 25m for 95% the time. Accuracy of position is measure by DOP- quantify and combine each source of error to calculate DOP.
Errors in GPS data
Ionosphere and troposphere delays:
Satellite signals slow as it passes through atmosphere. GPS system uses built in model that calculates an average amount of delay to partially correct for type of error.
Signal multipath:
GPS signal reflected off objects such as tall buildings increases travel of signal, causes errors.
Receiver clock errors:
Not as accurate as atomic clocks onboard GPS satellites may have slight timing errors.
Orbital errors:
Inaccuracy in satellites reported location
Intentional degradation of satellite signal:
Selective availability is intentional degradation of signal once I posed by US department of defence. Accuracy was decreased to 100m 95% of the time.
Differential GPS
Can be used to improve accuracy.
Techniques use 2 receivers:
Static base unit of precisely known location and roving receiver.
If both receivers are identically set up and used in close proximity, then positional error will be same for both units. In UK base states for differentiational correction are located in light houses.
GPS receiver
Shows relation to the WG884 data.
Most receivers convert this to any spatial reference system: British national grid.
Point data in GIS - explanation
Almost any feature can be represented as a point.
Extra non spatial information can be attached to that point and stored in a database.
Attributes give additional information about character of entities- good attribute makes a clear GIS output.
Applications of GIS point data
Surveying and field data collection.
Numerous applications in field- location of post offices etc
All geographers projects will benefit from mapping of features- a geographers shorthand.
Databases basic explanation
Collection of information that is organised that can be managed accessed and updated.
Developed by IBM in 50s in response to needs of military and business of government.
DBMS- database management systems- GIS is a competent of this
Software application that interacts with user, other applications and database itself to capture and analyse data eg Microsoft Acces.
Database concepts
User of application does not need to know how data is stored just how to access it- data transparency.
Changes can be made to database without effecting other components of system.
Database advantages
Reduction in data transparency, reduced software development costs, multiple external views the database depending on application.
Analysis only as good as attribute data.
Non data components of database
Operations: user functions for data manipulation eg sorting/ deleting records.
Data definition language: describe constants of data base- field attribute names.
Query language: standard language used to edit, analyse- input and output data.
File studies: several common data models- define how data is stored in system and they are connected to each other.
Data models- flat and relational files
Flat file- data on a single table- useful but simplistic cannot deal with relationship between objects- addressed using heirachical , network or relationship data.
Relational file- most popular data model and widely used in GIS. Each table has a key, common interger such as an ID appears in every ta le Iām database- several tables are easily linked.
Flat versus relation files
Flat models can be seen as cumbersome and lead to data repetition.
Relational models are: efficient in terms of storage and access, easy to update, allow different users to access selected information, more consistent with a greater integrity of data.
In flat file, both attribute data and spatial data in same file.
Relational model is more common where spatial data is stored as part of tables.
Vector topology definition
Heywood et al 2002- geomatics relationship between objects located in space.
Topology consist of 3 elements- Burough 1986- adjacency, containment and connectivity. Challenge is to mantain topology using minimum amount of data
Vector point data
Simplist type of spatial object.
Choice of entities to represent as points depends on scale of map- from individual buildings to cities.
If height is known, this can be added as an attribute effectively describing the point as an co ordinate- effectively uses database flat file.