CQL2 Query Language¶
CQL2 (Common Query Language 2) is an advanced query language used to filter and query spatial and attribute data within the 3DCityDB Tool. It allows users to define precise queries for exporting or deleting features based on attribute values, spatial properties, or logical conditions.
CQL2 is a standard maintained by the OGC (Open Geospatial Consortium) and serves as an evolution of the original CQL language, providing better expressiveness and flexibility for data filtering.
Key Features of CQL2
- Expressive Syntax: Combines logical operators with a rich set of functions for building complex queries.
- Spatial Filtering: Supports geospatial functions to filter data based on spatial relationships.
- Ease of Use: Simple, human-readable expressions that are easy to construct and interpret.
Using CQL2 with CityDBTool¶
CityDBTool allows the use of the -f or --filter option followed by a CQL2 expression to filter data when exporting or deleting records. This enables users to select only the relevant subset of data based on attribute values, spatial conditions, or both.
Syntax¶
The general syntax for using CQL2 with CityDBTool is:
Where <CQL2 Expression> is a valid CQL2 query that defines the filtering conditions for the data export.
Writing CQL2 Expressions¶
A CQL2 expression consists of attribute names, operators, and values. It can also include spatial functions to handle geospatial conditions.
Attribute Filtering¶
Filter based on attribute values using comparison operators such as =, !=, <, <=, >, and >=. Logical operators AND, OR, and NOT can be used to combine conditions.
Example¶
Spatial Filtering¶
Use spatial functions to filter based on the spatial relationship of geometries. Commonly used functions include:
intersects: Returns true if two geometries intersect.contains: Returns true if one geometry contains another.within: Returns true if one geometry is within another.