Lindorm:Query spatiotemporal objects

• The following table describes the predicates that can be used to query spatial data. In the table, Expression specifies a geometry in well-known text (WKT). A geometry can be a point, line, or polygon.

• Example 1: Query the geometries in the geographic extent (120E, 30N, 130E, 40N). The geometries can be restaurants, vessels, and vehicles.

// Query a DataStore.
DataStore ds = DataStoreFinder.getDataStore(params);
// Specify query conditions.
String schema = "schemaName";
String stFilter = "bbox(geom, 120,30,130,40)"
Query query = new Query(schema, ECQL.toFilter(stFilter));
// Obtain the query result.
SimpleFeatureCollection features=ds.getFeatureSource(schema).getFeatures(query);

• Example 2: Query the vehicles in a radius of 5 kilometers.

  • Build a polygon that covers the area in a radius of 5 kilometers. For example, you can set the geographic extent to (46.9 48.9, 47.1 48.9, 47.1 49.1, 46.9 49.1, 46.9 48.9).

  • Use the CONTAINS predicate to filter all objects.

  // Query a DataStore.
  DataStore ds = DataStoreFinder.getDataStore(params);
  // Specify query conditions.
  String schema = "schemaName";
  String stFilter =  "contains('POLYGON ((46.9 48.9, 47.1 48.9, 47.1 49.1, 46.9 49.1, 46.9 48.9))', geom)"
  Query query = new Query(schema, ECQL.toFilter(stFilter));
  // Obtain the query result.
  SimpleFeatureCollection features=ds.getFeatureSource(schema).getFeatures(query);

Spatiotemporal query

You can query spatial data based on the preceding description. This section describes how to query spatiotemporal data in different scenarios. For example, you want to query the trajectories of all the vehicles in the geographic extent (20E, 30N, 130E, 40N) in the last 2 hours.

Lindorm GanosBase supports the following predicates for temporal queries. In the following table, Expression specifies the name of the date column and Time specifies the date string in the UTC format.

Lindorm GanosBase supports various expressions for temporal queries. The following table describes the expressions.

• Example: If you want to query the trajectories of the vehicles that are in the geographic extent (120E, 30N, 130E, 40N) from 2014-01-01T11:45:00 to 2014-01-01T12:15:00, perform a spatiotemporal query. You can use the following sample code:

// Specify query conditions.
String schema = "schemaName";
String stFilter = "bbox(geom, 120,30,130,40) AND dtg DURING 2014-01-01T11:45:00.000Z/2014-01-01T12:15:00.000Z";
Query query = new Query(schema, ECQL.toFilter(stFilter));
// Obtain the query result.
SimpleFeatureCollection features=ds.getFeatureSource(schema).getFeatures(query);

Attribute query

• Lindorm GanosBase supports the following comparison operators: =, <>, >, >=, <, and <=. If you want to select a city that has a population of more than 15 million, define the query condition PERSONS > 15000000. The PERSONS field specifies the population.

• You can use the BETWEEN operator to specify a range. For example, you can use the following string to specify a population range: PERSONS BETWEEN 1000000 AND 3000000.

• The comparison operators support text values. You can specify a text value on the right side of the equal sign (=). For example, CITY_NAME='Beijing' specifies the city of Beijing. You can also use the LIKE operator in the same manner in which the operator is used in SQL statements. For example, CITY_NAME LIKE 'N%' specifies cities whose names start with the letter N.

• You can compare two attributes. For example, you can use MALE > FEMALE to query cities in which the population of male residents is greater than the population of female residents.

• Lindorm GanosBase supports the following arithmetic operators: plus (+), minus (-), multiply (*), and divide (/). For example, you can use the filter condition UNEMPLOY/(EMPLOYED + UNEMPLOY) > 0.07 to query all cities whose unemployment rate is greater than 7%.

• You can use the IN operator to specify an attribute whose values are in a specified range. You can use the IN operator in the same manner in which the operator is used in SQL statements. For example, you can use ID IN ('cities.1', 'cities.12') or CITY_NAME IN ('Beijing', 'Shanghai', 'Guangzhou') to query cities whose IDs or names contain the specified values.

• Lindorm GanosBase supports all the filter functions in GeoServer. For example, you can use strToLowerCase(CITY_NAME) like '%m%' to query cities whose names contain the letter M or m.

• To filter geometries, you can use the bounding box (BBOX). For example, you can use BBOX(the_geom, -90, 40, -60, 45) to query cities whose geographic coordinates are in the geographic extent (-90, 40, -60, 45).

// Specify query conditions.
String schema = "schemaName";
String filter = "name = 'bob'";
Query query = new Query(schema, ECQL.toFilter(filter));
// Obtain the query result.
SimpleFeatureCollection features=ds.getFeatureSource(schema).getFeatures(query);

Specify the columns that you want to return

To specify the columns that you want to return, set the parameters of the Query object. The following sample code provides an example:

// Specify the columns to be returned.
String[] returnFields={"geom"};
// Specify query conditions.
String schema = "schemaName";
String stFilter = "bbox(geom, 120,30,130,40)"
Query query = new Query(schema, ECQL.toFilter(stFilter));
query.setPropertyNames(returnFields);
// Obtain the query result set.
SimpleFeatureCollection features=ds.getFeatureSource(schema).getFeatures(query);

Specify a sorting method

You can set the parameters of a SortBy object to specify columns based on which data is sorted. The following sample code provides an example:

String sortField="name" //Specify the column in which you want to sort values.
FilterFactory2 ff = CommonFactoryFinder.getFilterFactory2();
SortBy[] sort = new SortBy[]{ff.sort(sortField, order)};
query.setSortBy(sort);
SimpleFeatureCollection features=ds.getFeatureSource(schema).getFeatures(query);