This topic describes TrajGiST indexing, which is an extension to GiST indexing. You can create a TrajGiST index on a column that stores trajectory data.

Background information

TrajGiST performs better than GiST in the following ways:

  • TrajGiST provides a better method that is used to estimate the overheads of indexes. If more than one index is created, TrajGiST can better select an index than GiST.
  • TrajGiST supports upward compatibility of indexes. If an accurate result cannot be obtained because the index does not provide sufficient information, you can still obtain a coarse-grained result by using an index-based scan. For example, you have created an index only on the t axis, but you want to call the ST_{2DT}Intersects function. In this case, you can filter out the trajectories that do not fall within a specified time range based on the index on the t axis.

Syntax

CREATE INDEX [index_name] on table_name USING TRAJGIST(traj_col [operator_family]);
  • index_name: the name of the index. This parameter is optional.
  • table_name: the name of the table to which the column belongs.
  • traj_col: the name of the column.
  • operator_family: the operator family that is used to create the index. Default value: trajgist_ops_3dt. This parameter is optional.
Note The created index accelerates queries that are run by operators and the following functions: ST_ndIntersect, ST_ndDWithin, ST_ndContains, and ST_ndWithin.

Supported operator families

The following table describes the operator families that are supported by GiST.

Operator family Description
trajgist_ops_z Creates an index on the z axis. This type of index supports queries that cover only the z axis.
trajgist_ops_t Creates an index on the t axis. This type of index supports queries that cover only the t axis.
trajgist_ops_2d Creates an index on the x and y axes. This type of index supports queries that cover only the x and y axes.
trajgist_ops_2dt Creates an index on the x, y, and t axes. This type of index supports queries that cover the x, y, and t axes.
trajgist_ops_3d Creates an index on the x, y, and z axes. This type of index supports queries that cover the x, y, and z axes.
trajgist_ops_3dt Creates an index on the x, y, z, and t axes. This type of index supports all of the queries that are supported by the preceding five operator families.
Note TrajGiST allows you to create an index on a single column. It does not allow you to create an index on multiple columns including the columns that store other types of data than trajectory data.