Vector data processing in GRASS GIS
Vector data import and export
The v.in.ogr module offers a common interface for many different vector formats.
In vector data the features are recorded one by one, with shape being defined by the numerical values of the pairs of xy coordinates.
We will start with an explanation of what Raster and Vector data mean.
Raster GIS data is stored in a grid of cells or pixels. Each cell contains a certain value and every location within that cell shares that value.
Vector data comes in the form of points and lines that are geometrically and mathematically associated. Points are stored using the coordinates, for example, a two-dimensional point is stored as (x, y).
Vector data provide for high precision in representing the location of features. Aronoff (1989) described how vector data can be used to define the location of a point, a line, and an area.
Vector data model: Divides space into discrete features, usually points, lines or polygons.
Dept. of English & Creative Writing, Bowland College, Lancaster University, Lancaster, LA1 4YT ...
Vector data scale dependency
For all vector datasets, you should always consider the scale dependency of spatial data. When should an airport be represented as a point, and when should it be a polygon?
Vector Data Formats
With the exception of the popular CAD formats, .dwg and .dxf, vector formats supported in GIS are extensions of the tabular types discussed above.
Vector Data: One method of storing, representing or displaying spatial data in digital form. It consists of using coordinate pairs (x,y) to represent locations on the earth.
The Vector Data Model
The Vector data model is similar in its operation to the join the dots books we all used as kids. An object's shape is represented by dots which are located where the shape of the object changes.
Vector data. These are ordered tuples of real values that represent fields of directions.
Vector data model
based on vectors (as opposed to space-occupancy raster structures)
fundamental primitive is a point ...
Vector data composed of simple lines with no topology and usually no attributes. Spaghetti lines may cross, but no intersections are created at those crossings.
Digitizing that does not identify intersections as it records lines.
Many vector datasets contain features that share geometry. For example, a forest border might be at the edge of a stream, lake polygons might share borders with land-cover polygons and shorelines, ...
World Vector Data
A vector base map for use in XMap that displays countries, major roads, cities, and airports for the entire world. It also includes a world elevation model for 3-D terrain viewing.
Scanned Vector Data Method
These data, sometimes referred to as, contour-to-grid, is a way to use the contour map information to produce gridded elevation data. The USGS, as well as the U.S.
See Also: vector data model
[data models] A representation of the world as a surface divided into a regular grid of cells.
OGR is the vector data access portion of the GDAL library. It provides access to a multitude of data formats.
Vector: Vector data is the storage of X, Y, Z coordinates connected to form points, lines, areas, and volumes. Vector data is best suited to store discrete, well-defined data that can clearly be delimited.
Raster and Vector Data
Spatial features in a GIS database are stored in either vector or raster form. GIS data structures adhering to a "vector" format store the position of map features as pairs of x, y (and sometimes z) coordinates.
Vector Data Structures
In computer Cartography and GIS, the vector data structures were first to be used because they were created simply from the digitizing tablets, they better represented the complex features like land parcels, ...
Vector Data A coordinate-based data structure commonly used to represent map features. Each linear feature is represented as a list of ordered x,y coordinates.
In dealing with vector data an important concept is that of topology. Topology, derived from geometrical mathematics, is concerned with order, contiguity and relative position rather than with actual linear dimensions.
The file size for vector data is usually much smaller for storage and sharing than raster data. Image or raster data can be 10 to 100 times larger than vector data depending on the resolution.
Some scanners also use software to convert raster data to vector data. scratch file A temporary file holding intermediate data during an operation, such as when calculating arc intersections, or building feature topology.
[LINK] Raster data files can be manipulated quickly by the computer, but they are often less detailed an may be less visually appealing than vector data files, which can approximate the appearance of more traditional hand-drafted maps.
However, the bulk of the introductory materials focus on vector data processing and applications with only minimal reference to grid-based map analysis.
A typical feature with respect to co-ordinate transformations is the possibility in ILWIS to match vector and raster data by an on-the-fly transformation of the vector data.
Heads-up digitizing: This is similar to the manual digitization, but the raster scanned data is imported and laid below the vector data to be traced on the computer screen itself.
VECTOR DATA FORMATS
RASTER DATA FORMATS
VECTOR AND RASTER - ADVANTAGES AND DISADVANTAGES
ATTRIBUTE DATA MODELS
SPATIAL DATA RELATIONSHIPS
CHAPTER 3: DATA SOURCES
SOURCES OF DATA
DATA INPUT TECHNIQUES ...
Raster data such as the DOQs, rather than vector data, may be more effectively used for some applications. Much like the symbology on a topographic map, vector data tend to be more generalized (i.e.
One of the three types of spatial data in a GIS (the others being image and vector data). Raster data represents geographic space as a matrix of cells; map features are defined by numeric values assigned to the cells.
As you probably know, a DEM is a raster file, as opposed to the vector data that AutoCAD and other CAD programs normally handle. So the data structure is basically an array of elevation values arranged on a rectangular pattern.
Working with Mixed Raster/Vector Data
Bentley Descartes allows immediate editing of raster and vector data, reducing costs associated with data maintenance.
Supported vector data formats include ArcInfo coverages, E00, or SHP files, MapInfo MIF and TAB data, GML or XML files, SDTS data, Microstation DGN and others.
First theoretic results in the creation of 3D vector data models, first practical results in voxel models for local mining systems;
Theoretical foundation of the quadtree (octree) indexing schemas; ...
Mathematical method to stretch or warp images to match existing vector data. Forces a digital map to fit a designated base.
coverage A digital version of a map forming the basic unit of vector data storage in ARC/INFO.
For a vector dataset, go to the field properties, select the Shape field, and use the '...' button next to the Spatial Reference property to edit the spatial referencing system. Note that your GIS data layers have ab inherent coodinate system.
A vector data product used for nautical navigation. ENC data is produced by nautical charting agencies throughout the world and uses the IHO (International Hydrographic Organization) S-57 standard for its database structure and attribution.
Coverage - (1) A digital map that forms the basic unit of vector data storage in Arc/Info. A coverage stores map data in the three basic forms of graphic elements, i.e. points, lines, polygons. (2) A single theme or layer of data (e.g.
MOSS vector data files contain strings of coordinate pairs which describe closed polygonal areas, lines, and single point features. Common boundaries between adjacent polygons are repeated twice in this data structure, once with each polygon.
Data Exchange Format. A format for storing vector data in ASCII or binary files; used by AutoCAD and other CAD software and convertible to ARC/INFO coverages.
Spatial Data Features - In a vector data model, typically points, lines or areas (polygons); in a raster data model, a contiguous collection of grid cells with like values.
Drawing Exchange Format (DXF)
An exchange format for CAD files. A format for storing vector data in ASCII or binary files; used by AutoCAD and other CAD software and convertible to ARC/INFO coverages.
GIS Acronyms ...
A commercial PC-based GIS. The software package uses the vector data model and is primarily intended for business applications.
cartographic spaghetti: A loose data structure for vector data, with only order as an identifying property of the features.
Vector data is comprised of lines or arcs, defined by beginning and end points, which meet at nodes. The locations of these nodes and the topological structure are usually stored explicitly.
See also: Vector, Information, Raster, GIS, Map