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 the features are recorded one by one, with shape being defined by the numerical values of the pairs of xy coordinates.
Vector Data Models Structures
Vector data models can be structured many different ways. We will examine two of the more common data structures here.
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.
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?
: 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.
Discrete features, such as customer locations, are usually represented using the vector model. Features can be discrete locations or events, lines, or areas.
Vector data. These are ordered tuples of real values that represent fields of directions.
based on vectors (as opposed to space-occupancy raster structures)
fundamental primitive is a point ...
data that are described by coordinates of their points. There can be several data types: points, lines, polygons, multipoints, multilines, multipolygons
don't ask it, ask a specific question, i.e. what is the extension of the file?
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, ...
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: 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.
The model uses discrete point and line segments to identify the locations of the Earth's features.
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.
In computer Cartography and GIS, the 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 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 . 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 processing and applications with only minimal reference to grid-based map analysis.
Raster references spatial data according to a grid of cells (or pixels), whereas vector data references spatial data to a series of coordinates. Raster data consist of different numerical values assigned to individual pixels.
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 .
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.
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.
See also: Vector, Information, Raster, Map, GIS