GDDD
- No information available:
- The method or technique applied for the data capture is either unknown or is not included in the classification
- Census:
- A census is an official survey of the population of a country. Census data are alpha/numeric data. The geographical references of census data are often indirect.
- Field survey:
- The geometry of the geographical features is determined by using terrestrial measurements, e.g. polar measurements and levelling with reference to the geodetic network. The geometric form of field surveyed data is vector. The geographic features are identified at the source by field observations.
- Manual digitising:
- The base data for manual digitised data are analogue maps (paper maps). The geometry of the map features is digitised using a digitising tablet and geographically referenced by coordinate transformations. The geometric form of manual digitised data is vector. The identification of the geographic features relies on the method used for capturing the original analogue data.
- Photogrammetry:
- The geometry of the geographical features is determined by digitising (aerial) photographs. Usually the geometric form of photogrammetic data is vector but raster data might also be produced by photogrammetry, e.g. digital orthophoto maps. The geographical features are identified by their appearance in the photograph.
- Remote sensing:
- Remotely sensed data are usually acquired from air or space borne sensors, e.g. multispectral scanners and radars. The remote sensing dataset consists of a set of raster images where each pixel represents the intensity of the reflection/echo of a geographical area in specified band of the electro magnetic spectrum. The geographic features may be identified by image interpretation with or without ground control data.
- Scanning:
- The base data for scanning are analogue data (paper maps). The map is decomposed with the aid of an image scanner into a number of adjacent image elements (pixels) forming a digital image of the map. The geographical features may be identified by the user.
MEGRIN accepts no responsibility as to the completeness or accuracy of the information.