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.
Vector Data Models Structures
Vector data models can be structured many different ways. We will examine two of the more common data structures here.
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. A point is represented by a simple pair of coordinates.
~ model: Divides space into discrete features, usually points, lines or polygons.
Dept. of English & Creative Writing, Bowland College, Lancaster University, Lancaster, LA1 4YT ...
~ scale dependency
For all ~sets, 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. Features can take the form of single points, lines, arcs or closed lines (polygons) (see Raster Data).
The ~ Model
The ~ 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. The dots are joined by straight lines.
Discrete features, such as customer locations, are usually represented using the vector model. Features can be discrete locations or events, lines, or areas. Lines, such as streams or roads, are represented as a series of coordinate pairs.
~. These are ordered tuples of real values that represent fields of directions. For example, hydraulic gradients (for two-dimensional groundwater models), wind velocities (again for two-dimensional models), and ocean currents are two-dimensional vector fields.
~: GML2, GML3, SHP files, KML, WKT (Well-known Text), DGN, JSON
Raster Data: Geotiff, AsciiGrid, NetCDF, JPEG, PNG, HDF-EOS, ERDAS HFA
Outputs can be stored in GeoServer/MapServer
A browser based client ...
based on vectors (as opposed to space-occupancy raster structures)
fundamental primitive is a point ...
~ 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 ~sets 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, and parcel polygons might be covered by parcel lot lines.
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 ~ 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. Raster models are useful for storing data that varies continuously, as in an aerial photograph, a satellite image, a surface of chemical concentrations, or an elevation surface.
OGR is the ~ 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 objects usually do not fill space like raster layers do; they depict where features occur and the space around those features is empty.
Vector: ~ is the storage of X, Y, Z coordinates connected to form points, lines, areas, and volumes. ~ 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, ...
~ A coordinate-based data structure commonly used to represent map features. Each linear feature is represented as a list of ordered x,y coordinates. Attributes are associated with the feature (as opposed to a raster data structure, which associates attributes with a grid cell).
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 ~ is usually much smaller for storage and sharing than raster data. Image or raster data can be 10 to 100 times larger than ~ depending on the resolution. Another advantage of ~ is it can be easily updated and maintained.
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. SDTS/TVP Spatial Data Transfer Standard/Topological Vector Profile.
[LINK] Raster data files can be manipulated quickly by the computer, but they are often less detailed an may be less visually appealing than ~ 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. What has been lacking is a grid-based teaching package that seamlessly interfaces with desktop mapping systems and teaching approaches.
Raster references spatial data according to a grid of cells (or pixels), whereas ~ 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 ~ 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
DATA EDITING AND QUALITY ASSURANCE ...
Raster data such as the DOQs, rather than ~, may be more effectively used for some applications. Much like the symbology on a topographic map, ~ tend to be more generalized (i.e.
One of the three types of spatial data in a GIS (the others being image and ~). 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 ~ that AutoCAD and other CAD programs normally handle. So the data structure is basically an array of elevation values arranged on a rectangular pattern. The data object is the node. There is one node per array location.
Working with Mixed Raster/~
Bentley Descartes allows immediate editing of raster and ~, reducing costs associated with data maintenance.
First theoretic results in the creation of 3D ~ models, first practical results in voxel models for local mining systems;
Theoretical foundation of the quadtree (octree) indexing schemas;
Theoretical results in application the hypergraph theory for spatial objects; ...
Mathematical method to stretch or warp images to match existing ~. Forces a digital map to fit a designated base.
coverage A digital version of a map forming the basic unit of ~ storage in ARC/INFO. A coverage stores map features as primary features (such as arcs, nodes, polygons, and label points) and secondary features (such as tics, map extent, links, and annotation).
For a ~set, 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.
Once it is all set up you can upload aerial or satellite imagery onto your PDA with any other ~ and bring it out in the field with your.
The ESRI Shapefile or simply a shapefile is a popular geospatial ~ format for geographic information systems software. It is developed and regulated by ESRI as a (mostly) open specification for data interoperability among ESRI and other software products. See also: .shp Synonyms: .
A ~ 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. [Category=Geospatial ] ...
When you use Data Connect to bring in ~ (e.g. SDF, SHP, SQL Server Spatial), you notice an option to Add to Map with Query. This option is not available for the Raster provider; there's simply one option: Add to Map.
This is as designed.
A commercial PC-based GIS. The software package uses the ~ model and is primarily intended for business applications.
The different characteristics within a set of data to be mapped into ArcGIS.Attributes are defined within a table and displayed on a theme.
Coverage - (1) A digital map that forms the basic unit of ~ storage in Arc/Info. A coverage stores map data in the three basic forms of graphic elements, i.e. points, lines, polygons.
Drawing Exchange Format (DXF)
An exchange format for CAD files. A format for storing ~ in ASCII or binary files; used by AutoCAD and other CAD software and convertible to ARC/INFO coverages.
DEM - Digital Elevation Model ...
The OpenLayers plugin is a great tool for presenting your ~ layers on top of Google, Bing, Yahoo and OpenStreetMap thematic layers. To add the layer select Plugins
OpenLayers plugin ...
Spatial Data Features - In a ~ model, typically points, lines or areas (polygons); in a raster data model, a contiguous collection of grid cells with like values.
and outputs usually an xml document containing a GML encasement that lists the attributes and ~ for each feature
DescribeFeatureType - a web method which provides meta data about requested feature types or type such as the attributes, number of features etc.
Shapefile - A proprietary ~ storage format for storing the location, shape, and attributes of geographic features.
Scale - The ratio or relationship between a distance or area on a map and the corresponding distance or area on the ground, commonly expressed as a fraction or ration.
63 a technique applied to simple ~ structures to embed inner rings within outer rings. A line that is repeated (drawn twice) should not appear graphically. ridge p. 161 line along which a surface diverges in two different directions. (Topology of topography) ring p.
~ 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: What is the meaning of Vector, Raster, Information, GIS, Map?