1. What is GIS?
2. What is OGC?
3. What are the main OGC services in order to create the simplest GIS?
4. Is there any relation between ISO (International Standard Organization) and OGC?
OGC has a close relationship with ISO/TC 211 (Geographic Information/Geomatics). The OGC abstract specification is being progressively replaced by volumes from the ISO 19100 series under development by this committee. Further, the OGC standards Web Map Service and Simple Features are ISO standards. GML will soon be approved as an ISO standard.
5. What is WMS?
Web Map Service produces maps from geographic data. A map is not the data itself. Maps create information from raw geographic data. Maps are generally rendered in pictorial formats such as jpeg, GIF, png. WMS also produce maps from vector-based graphical elements in Scalable Vector Graphics (SVG).
WMS provides three operations protocols (GetCapabilities, GetMap, and GetFeatureInfo) in support of the creation and display of registered and superimposed map like views of information that come simultaneously from multiple sources that are both remote and heterogeneous.
Basically there are two types of WMS defined in the specifications. These are basic WMS and SLD-enabled WMS. For the basic WMS, there are three operations defined. These are getCapabilities, getMap, GetFeatureInfo.
WMS publishes its ability and data holdings in its capabilities document. This document is encoded in XML. WMS classifies its geographic data holdings in the “Layers” and gives information about the styles available for these Layers. Each layer can have sub layers and the sub layers can have different styling defined for them.
A Web Map Service is usually not invoked directly. More often, it is invoked by a client application that provides the user with interactive controls. This client application may or may not be web-based
6. What is WFS?
Web Feature Service (WFS) is an intermediary server sitting in front of the archived data kept in the Databases or files systems and, provides data manipulation operations.
Clients interact with a Web Feature Service by submitting database queries encoded in Open Geospatial Consortium Filter Encoding Implementation and in compliance with the Open Geospatial Consortium’s Common Query Language.
As a minimal requirement a basic Web Feature Service should be able to provide requested geographical information as Geographic Markup Language feature collections. However, more advanced versions also support “create, update, delete and lock operations”. Three operations must be supported by a basic Web Feature Service: GetCapabilities, DescribeFeatureType and GetFeature.
7. What is GML?
GML is an XML encoding for the transport and storage of geographic information, including both the spatial (attributes) and non-spatial (geometric) properties of geographic features. GML defines a data encoding in XML that allows geographic data and its attributes to be moved between disparate systems with ease XML encoding of geospatial information. It is human-readable and separates contents from presentation. Presentation is basically represented under the “geometry” tag elements.
If some one wants to define a GML schema for a feature, he should import the Geometry schema (geometry.xsd) the Feature Schema (feature.xsd) and the XLinks schema (xlinks.xsd) as base schemas.
WMS requests feature data from the WFS in the form of GML. WFS store and serve the geospatial data encoded in GML.
8. What is feature?
A feature is an abstraction of a real world phenomenon; it is a geographic feature if it is associated with location relatives to the earth such as faults, rivers, roads, lakes. All the feature instances should be created according to the schema files and encoded in GML.
9. What are the vector and raster data?
Vector data deals with discrete phenomena, each of which is conceived of as a feature. The spatial characteristics of a discrete real world phenomenon are represented by a set of one or more geometric primitives (points, curves, surfaces, or solids). Other characteristics of the phenomenon are recorded as feature attributes. Usually, a single feature is associated with a single set of attribute values.
Raster data deals with real world phenomena that vary continuously over space. It contains a set of values, each associated with one of the elements in a regular array of points or cells. It is usually associated with a method for interpolating values at spatial positions between the points or within the cells.
10. What is coverage data?
OGC uses the term “coverage” to refer to any data representation that assigns values directly to spatial position. Coverage is a feature that associates positions within a bounded space (its spatiotemporal domain) to feature attribute values (its range). Examples include a raster image, a polygon overlay, or a digital elevation matrix. The spatio-temporal domain of coverage is a set of geometric objects described in terms of direct positions. Commonly used spatio-temporal domains include point sets, grids, collections of closed rectangles, and other collections of geometric objects.
11. What is spatial and geo-spatial data?
Spatial data are a kind of data that pertains to the space occupied by objects. Example spatial data from the real world are cities, rivers, roads, states, crop coverage, mountain ranges etc. In the implementation these are represented by points, lines, rectangles, surfaces, volumes and etc. Spatial data have some common characteristics. These type of data are geometric data and in high dimensions. These data can be either discrete (vector) or continuous (raster). GIS applications are applied on these types of data.
Geospatial data are spatial data associated with a location relative to the Earth.
12. What is the term “capability” in OGC used for?
Each GIS service defined in OGC has a capability file encoded in XML. There is no common format for the capability valid across all the OGC defined services. All the OGC services has getCapability service interface in order to return capabilities metadata. Capabilities function as “service” metadata, providing information about what the service offers. Clients to the services determine whether they can work with that server based on its capabilities.
No comments:
Post a Comment