Vector Data

Vector data are spatial object representations with associated features (attributes/variables).

Vector data models:

  1. Vector geometry: Faster computations, but extra work for maintenance.
    • 0D: point;
    • 1D: linestring;
    • 2D: polygon;
    • Geometry collection: multi-point, multi-linestring, multi-polygon;
  2. Vector topology: Common boundary between two adjacent areas are stored as a single boundary, so that gaps and slivers are impossible.
    • Basic types:
      • 0D: point, centroid, kernel (3D centroid);
      • 1D: line, boundary;
      • 2D: face (3D area);
    • Derived types:
      • 0D: node (end of lines/boundaries); vertex (non-node points);
      • 2D: area = closed ring of boundaries + centroid; isle = closed ring of boundaries without centroid;
      • 3D: volume = faces + kernel;

Popular formats: Shapefile; OpenStreetMap file formats; GeoJSON; GML;

ESRI Shapefile and implementations of Simple Features are non-topological vector formats.

GeoJSON

GeoJSON is a JSON extension implementing Simple Features. Native to JavaScript, GeoJSON is a popular format for serving geospatial data on the web, such as drawing leaflet maps or sending vector tiles. Unlike CSV, GeoJSON does not have simple separators between data entries or well-defined types and orders, thus not perfect for streaming.

A GeoJSON feature is an object of "type": "Feature" with geometry and additional properties. A FeatureCollection object is a set of features.

GeoJSON supports the following geometry type specified with coordinates:

  • Point: a single position, specified as an ordered array [longitude, latitude, height];
  • LineString: an array of positions;
  • Polygon: a collection of LinearRing (loops of positions) specifying exterior (counterclockwise) and interior (clockwise) boundaries;
  • Multi-part collections of these types: MultiPoint, MultiLineString, and MultiPolygon.
  • (rare) GeometryCollection is a container for different kinds of geometries.

An awesome list of GeoJSON utilities compiled by Tom MacWright.

Well Known Text

WKT (Well Known Text) Representation (of Simple Features 1.2 geometries):

  1. Point: POINT(- 117.25 35.0)
  2. Line String: LINESTRING(0 10, 20 15, 30 15)
  3. Polygon: POLYGON((0 0,10 10,10 0,0 0),(3 1,4 1,4 2,3 1))
  4. Polyhedral Surface: POLYHEDRALSURFACE(((0 10,0 0,10 0,10 10,0 10)),((0 10,5 15, 10 10,0 10)))
    1. TIN (Triangulated Irregular Netowrk)
  5. Geometry Collection:
    1. Multi Point: MULTIPOINT((0 0),(10 10),(10 0))
    2. Multi Line String: MULTILINESTRING((0 0,10 10,10 0),(3 1,4 1,4 2,5 1))
    3. Multi Polygon: MULTIPOLYGON(((0 0,10 10,10 0,0 0),(3 1,4 1,4 2, 3 1)),((20 20, 30 30, 30 20, 20 20)))

Geography Markup Language

GML (Geography Markup Language) is an OGC Standard, defined as an XML schema (written in XSD). GML profiles are restricted subsets of the full GML standard, such as GML Point Profile, GML Simple Features profile, and GML in JPEG 2000. GML application schemas are domain or community specific extensions of GML, with extra GML-defined XML vocabulary in a new namespace, such as CityGML, SensorML, Coverages.

GML has a very broad schema set:

Feature, Coordinate reference system, Geometry; Topology; Coverage (including geographic images), Unit of measure, Observations; Directions; Time, Dynamic feature; Map presentation styling rules.

An example file snippet in GML Simple Features:

<gml:Point gml:id="p1" srsName="http://www.opengis.net/def/crs/EPSG/0/4326">
    <gml:coordinates>45.67,88.56</gml:coordinates>
</gml:Point>
<gml:LineString gml:id="l1" srsName="http://www.opengis.net/def/crs/EPSG/0/4326">
    <gml:coordinates>45.67,88.56 55.56,89.44</gml:coordinates>
</gml:LineString>
<gml:Polygon>
    <gml:outerBoundaryIs>
        <gml:LinearRing>
            <gml:coordinates>0,0 100,0 100,100 0,100 0,0</gml:coordinates>
        </gml:LinearRing>
    </gml:outerBoundaryIs>
</gml:Polygon>

GPS Exchange Format

GPX (GPS Exchange Format) is an XML schema describing:

  • waypoints (wptType): recorded locations;
  • tracks (trkType): one ordered list of waypoints for each continuous span of GPS connection;
  • routes (rteType): an ordered list of routepoints, which represent significant turns or stage points for trip planning.

Latitude and longitude are expressed in decimal degrees using the WGS 84 datum. Elevation is recorded in meters. Dates and times are in Coordinated Universal Time (UTC) using ISO 8601 format.

Rater Data

Raster data are observations embedded in a regular geospatial grid.

Raster data file formats:

  1. lossless: .gif, .png, .tiff;
  2. lossy: .jpg;

TIFF (Tagged Image File Format) was developed by Aldus, now Adobe Systems. GeoTIFF is a public domain metadata standard which allows georeferencing information to be embedded within a TIFF file.

Imagery

Aerial photogrammetry (such as orthoimagery) and satellite imagery are spatially referenced. Example data sets include land cover.

Point clouds are 3D point data collected from laser scanning (LiDAR).

Other File Formats

NetCDF (Network Common Data Form) supports array-oriented scientific data, specifically digital geospatial information representing space and time-varying phenomena.

HDF (Hierarchical Data Format) is a multi-object file format for storing and transferring graphical and numerical data mainly used in scientific computing. HDF supports several data models: multidimensional arrays, raster images, and tables.

OpenCV (Open Computer Vision) provides low level portable data types and operators, and a set of high level functionalities for video acquisition, image processing and analysis, structural analysis, motion analysis and object tracking, object recognition, camera calibration and 3D reconstruction.

KML

KML (formerly Keyhole Markup Language) is a 3D portrayal format for geographic data. KML is also an OGC standard, defined as an XML schema.

KML Language Reference defines annotation of maps and images, presentation of graphical data on the globe (3D models, photo overlay), and camera movement.

KML is native to Google Earth, where you can create and display KML files. KML text files (.kml) and related images can be archived into a ZIP file (.kmz). Besides Google Earth, KML files can be displayed in ESRI ArcGIS, Adobe PhotoShop, Autodesk AutoCAD, and NASA World Wind.

🏷 Category=Geographic Information System