Geography¶
Geography is a data type composed of latitude and longitude that represents geospatial information. NebulaGraph currently supports Point, LineString, and Polygon in Simple Features and some functions in SQL-MM 3, such as part of the core geo parsing, construction, formatting, conversion, predicates, and dimensions.
Type description¶
A point is the basic data type of geography, which is determined by a latitude and a longitude. For example, "POINT(3 8)" means that the longitude is 3° and the latitude is 8°. Multiple points can form a linestring or a polygon.
Note
You cannot directly insert geographic data of the following types, such as INSERT VERTEX any_shape(geo) VALUES "1":("POINT(1 1)"). Instead, you need to use a geography function to specify the data type before inserting, such as INSERT VERTEX any_shape(geo) VALUES "1":(ST_GeogFromText("POINT(1 1)"));.
| Shape | Example | Description |
|---|---|---|
| Point | "POINT(3 8)" |
Specifies the data type as a point. |
| LineString | "LINESTRING(3 8, 4.7 73.23)" |
Specifies the data type as a linestring. |
| Polygon | "POLYGON((0 1, 1 2, 2 3, 0 1))" |
Specifies the data type as a polygon. |
Examples¶
//Create a Tag to allow storing any geography data type.
nebula> CREATE TAG IF NOT EXISTS any_shape(geo geography);
//Create a Tag to allow storing a point only.
nebula> CREATE TAG IF NOT EXISTS only_point(geo geography(point));
//Create a Tag to allow storing a linestring only.
nebula> CREATE TAG IF NOT EXISTS only_linestring(geo geography(linestring));
//Create a Tag to allow storing a polygon only.
nebula> CREATE TAG IF NOT EXISTS only_polygon(geo geography(polygon));
//Create an Edge type to allow storing any geography data type.
nebula> CREATE EDGE IF NOT EXISTS any_shape_edge(geo geography);
//Create a vertex to store the geography of a polygon.
nebula> INSERT VERTEX any_shape(geo) VALUES "103":(ST_GeogFromText("POLYGON((0 1, 1 2, 2 3, 0 1))"));
//Create an edge to store the geography of a polygon.
nebula> INSERT EDGE any_shape_edge(geo) VALUES "201"->"302":(ST_GeogFromText("POLYGON((0 1, 1 2, 2 3, 0 1))"));
//Query the geography of Vertex 103.
nebula> FETCH PROP ON any_shape "103" YIELD ST_ASText(any_shape.geo);
+---------------------------------+
| ST_ASText(any_shape.geo) |
+---------------------------------+
| "POLYGON((0 1, 1 2, 2 3, 0 1))" |
+---------------------------------+
//Query the geography of the edge which traverses from Vertex 201 to Vertex 302.
nebula> FETCH PROP ON any_shape_edge "201"->"302" YIELD ST_ASText(any_shape_edge.geo);
+---------------------------------+
| ST_ASText(any_shape_edge.geo) |
+---------------------------------+
| "POLYGON((0 1, 1 2, 2 3, 0 1))" |
+---------------------------------+
//Create an index for the geography of the Tag any_shape and run LOOKUP.
nebula> CREATE TAG INDEX IF NOT EXISTS any_shape_geo_index ON any_shape(geo);
nebula> REBUILD TAG INDEX any_shape_geo_index;
nebula> LOOKUP ON any_shape YIELD ST_ASText(any_shape.geo);
+---------------------------------+
| ST_ASText(any_shape.geo) |
+---------------------------------+
| "POLYGON((0 1, 1 2, 2 3, 0 1))" |
+---------------------------------+
When creating an index for geography properties, you can specify the parameters for the index.
| Parameter | Default value | Description |
|---|---|---|
s2_max_level |
30 |
The maximum level of S2 cell used in the covering. Allowed values: 1~30. Setting it to less than the default means that NebulaGraph will be forced to generate coverings using larger cells. |
s2_max_cells |
8 |
The maximum number of S2 cells used in the covering. Provides a limit on how much work is done exploring the possible coverings. Allowed values: 1~30. You may want to use higher values for odd-shaped regions such as skinny rectangles. |
Note
Specifying the above two parameters does not affect the Point type of property. The s2_max_level value of the Point type is forced to be 30.
nebula> CREATE TAG INDEX IF NOT EXISTS any_shape_geo_index ON any_shape(geo) with (s2_max_level=30, s2_max_cells=8);
For more index information, see Index overview.