1WKT (Well-Known-Text) is a textual representation of the vector geometry and coordinate system.
2WKB (Well-Known-Binary) is the binary equivalent of the WKT.
3SRID (Spatial Reference System Identifier) is the basis for defining the projected, unprojected, and local SRSs (CRSs).
WKT is a human readable representation of the spatial objects like:
- Point, Multipoint
- LineString, MultiLineString
- Polygon, Multipolygon, Triangle
- CircularString
- Curve, MultiCurve, CompoundCurve
- CurvePolygon
- Surface, MultiSurface, PolyhedralSurface
- TIN (Triangulated Irregular Network)
- GeometryCollection
Types of WKB
- Point, Multipoint
- LineString, MultiLineString, CircularString, GeodesicString
- Polygon, Multipolygon, CurvePolygon
- Surface, MultiSurface, Polyhedral Surface, CompoundSurface, BrepSolid
- Triange, TIN (Triangulated irregular network)
- Geometry Collection
- Curve, CompoundCurve, MultiCurve, CurvePolygon, EllipticalCurve, NurbsCurve, Clothoid, SpiralCurve
- Circle
- AffinePlacement
3D (three-dimensional) geometry is denoted by the letter “Z” after the geometry type. Geometry with a linear referencing system is denoted by the letter “M” after the geometry type.
The geometric coordinates can be 2D (x, y), 3D (x, y, z), 4D (x, y, z, m) with the m-value part of the linear referencing system or 2D with an m value (x, y, m).
! NOTE
WKT reflects points in order of long (longitude)-lat (latitude) while most formats use the order of lat-long. The reason WKT has the reverse order is that lat represents north/south direction of a point and long represents east/west direction of a point. In this way, WKT refers to a point in its (x,y) coordinates, and it converts to long-lat.
GeoJSON follows the same order as WKT.
CSV format contains a WKT column with WKT geometry.
WKT and WKB variants:
- EWKT (Extended Well-Known Text) and EWKB (Extended Well-Known Binary) is extended with SRID3 and 4 coordinate values (XYZM).
- AGF Text – is an extension of the OGC standard, includes curved elements.
