Sources of Data
August 26, 2011 § Leave a comment
Sources of Digital Data
There are various free and low-cost global data sets. (Such as the ‘Geography Network’, ‘National Imagery and Mapping Agency’, ‘USGS’, ‘ECAI Cleaninghouse’. Also software data like the ‘ESRI World Data’, and ‘Digital Chart of the World’). (Note: ESRI = Environmental Science Research Institiute). Though the DCW (Digital Chart of the World), is quite out of date, it still is quite useful for historic data, identifying abandoned buildings (e.g. for military), railways, even critical airplane landing strips.
Data can also be accessed online, such as ArcGis’ online base maps, ‘ArcGIS Online’. Much data is also offered by the U.S., with U.S. geodata, USGS – U.S. Geological Survey (such as TIGER (Topologically Integrated Geographic Encoded Reference Data), which shows ‘current’ streets, rivers, political boundaries etc. TIGER is commonly used for street addresses, containing centre liners for all streets.). The U.S. Geographic Names Index is also available, and interestingly contains historic names. Notable online examples also include ‘Google Maps / Earth’, ‘Electronic Cultural Atlas Initiative’ and ‘Community GIS’ (which was a communal UK response to the enforced price on postcodes).
Most of our free / low-cost local data comes from ‘Geoscience Australia’. The National Mapping Division offers a free 1:1 million global data set of infrastructure, DEM, vegetation, etc. Many books have been published with such free data. A 1:250,000 topographic map series, of vector data and map sheet images is also available now. The Gazetteer of Australia contains a collection of geographic names, represented by identifying numbers, which are important to reference in ArcGIS. (Like the Chinese 12th Century gazetteers, these geographical indexes are important to maps.) The Land Department NSW offers Parish maps, and the Gazetter of NSW (which is still error-prone). NSW Lands also offers SIX (Spatial Information Exchange), a comprehensive source of geospatial data.
Conventional Databases offer point data, providing attributes for line and area objects, under the common ‘CSV’ (comma separated value) format.
Digital Vector Data Sources include Non-geographical sources like Drafting / Surveyor’s (DXF) and geographically referenced sources. The latter sources (as above) include Worldwide, DCW, USGS, National Mapping Data, or other (e.g. NPWS – NSW National Parks and Wildlife Service).
Digital Survey Methods.
Map Digitising involves factors; Accuracy, Costs, Heads-Up/Down, Projection, Geodetic System, Topology. They can be executed on historical maps and plans, potentially through ArcGis’ ArcSCAN that converts raster-to-vector data. Digitized site plans (like Angkor Wat) are future-proofed, and can be modelled and animated.
Aerial Photographs can be corrected as Orthophotographs, provide 3d Models, 2d approximations, and go through heads-up digitizing.
Satellite Images facilitates georeferencing, can be at different resolutions (80/30/15/10/5/3/2), and obtainable through multi-band sensors – Synthetic Aperture Radar (MB-SAR), Stereo Pairs, and then Image Processing / Classification. Angkor is an example of its use.
Geophysical Methods include GPR (Ground Penetrating Radar), Magnetometry (mapping soil’s magnetism patterns), and Resistivity (ground electricity).
Global Navigation Satelite Systems (GNSS) provide site location co-ordinates, utilized for attribute collection / data loggers, can be ‘directly’ digitized, and involve external sensors (like laser rangefinders). Differential Correction achieved through post processing, e.g. through RTCM’s (Radio Technical Commission for Maritime Services) protocol Ntrip. Agios Georgios Kythera had this method applied to it.
Moving Maps / Navigation .
Total Station and Conventional Survey are used in architectural surveys.
Field Survey and Recording used at sites, considers survey units / material count, and individual artefact locations.
Excavation can consist of units and features as objects, 3D Volumetric Systems / Voxels, and have involved vastly increased data requirements.
Artefacts such as the Garden Island Engravings, demonstrate the scalability of GIS, utilizing the power of Total Stations (similar technical process to Ladar), producing a DEM, Digital Elevation, Model, 3D Engravings like a draped image.