This topic describes some basic concepts of spatio-temporal geometries.

Spatio-temporal geometries

Spatio-temporal geometries in DLA Ganos involve the following items:
  • Objects of spatio-temporal geometries.
    • Vector data, such as points, lines, and planes.
    • Spatio-temporal data, which consists of vector data and temporal attributes and is also referred to as spatio-temporal trajectory data.
  • Operations that can be performed on objects of spatio-temporal geometries, such as spatial relationship verification.

Spatio-temporal indexes

DLA Ganos has excellent query performance. When you use DLA Ganos to query data, it creates an efficient index for spatio-temporal data based on the spatial filling curve model in an underlying NoSQL database. For example, row key indexes are used for spatio-temporal data in ApsaraDB for HBase Enhanced Edition (Lindorm). For more information, see Create an index table.

Spatio-temporal relationships

A spatio-temporal relationship describes the relative locations of two geometries in time and space. Typical spatio-temporal relationships include INTERSECT, DISJOINT, OVERLAP, and CONTAIN. A geofence usually refers to the relationships of the geofences of an area to an object. The object can be a point, line, or plane. If the object is within the geofences, the area contains the object. If the object is outside the geofences, the area and object are disjoint.

OGC

Open Geospatial Consortium (OGC) is an international voluntary consensus standards organization. It has created a set of standards for data models and related operations. Geographic information system (GIS) vendors develop their GISs based on these standards to ensure spatial data interoperability.

GeoTools

The SDK of DLA Ganos is developed based on GeoTools. GeoTools is a library that provides tools to process geospatial data. It complies with OGC standards and can interact with standard OGC data models and interfaces. A large number of GISs are developed based on GeoTools. For more information, see https://geotools.org/.

Geometry

A geometry in OGC is defined as a spatial object, such as a point, line, or plane. A geometry contains only location information of a spatial object. It does not contain any attribute information. GeoTools provides tools for you to build geometries when you use DLA Ganos.

SimpleFeature

It specifies simple features. A SimpleFeature contains geometries and other attributes. A trajectory point is a SimpleFeature. The SimpleFeature contains the location information, temporal information, and other attributes of the trajectory point. The temporal information is also a part of the attribute information.

CQL&ECQL

Common query language (CQL) is a language defined by OGC to support geospatial data queries. Extended common query language (ECQL) is a more powerful extension of CQL. In most cases, ECQL is used to define filters by using SQL-like WHERE clauses. It uses well-known text (WKT) to obtain the destination filter. For more information, see Query spatio-temporal objects. In this topic, CQL is referred to as ECQL.

WKT

WKT is a text markup language defined by OGC to describe spatial objects. For example, a point can be represented by using POINT(0,0). WKT is commonly used in query statements and is much easier to read. CQL and ECQL also use WKT to describe spatial objects. For information about the detailed specifications of WKT, see http://www.opengeospatial.org/standards/wkt-crs.

WKB

Well-known binary (WKB) is a language defined by OGC to mark geometries by using serialized bytes. WKB data is less than WKT data. You can use WKB for data transmission. GeoTools provides a tool for you to convert between WKB data and WKT data.

Spatio-temporal geometric model of DLA Ganos

DLA Ganos uses the SimpleFeature model defined in OGC standards as its vector data model. Geometric objects include point, linestring, polygon, multipoint geometry, multilinestring, and multipolygon. Geometries are loaded by the serverless Spark engine and used to compute data in the form of user-defined data type (UDT).

DLA Ganos supports the following vector data sources:
  • PolarDB
  • ApsaraDB for HBase Enhanced Edition (Lindorm)
  • HDFS
  • GeoMesa