This topic describes spatial references and the spatial reference table.
Overview
A spatial reference system (SRS) defines how to associate various spatial objects in GanosBase with specific positions on the Earth's surface.
SRSs are mainly divided into the following three types:
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Geographic coordinate system: directly maps to the Earth's surface by using longitude/latitude. The unit is degrees.
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Projected coordinate system: uses mathematical projection transformations to flatten the spherical surface of the Earth onto a plane.
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In a projected coordinate system, you can directly calculate distances, areas, angles, and so on.
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A projected coordinate system is a Cartesian coordinate system with a defined origin and two orthogonal axes.
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Each projected coordinate system defines its own units, typically meters or feet.
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Each projected coordinate system usually has its own applicable coordinate range.
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Local coordinate system: a Cartesian coordinate system that does not use the Earth's surface as a reference.
Spatial reference table
The spatial_ref_sys table is a built-in spatial reference table in GanosBase that conforms to the OGC standard. It lists more than 8,500 known spatial reference systems along with the details required for transformations and reprojections between them. You can also construct custom projections that conform to the PROJ4 standard.
The structure of the spatial reference table is as follows:
|
Column |
Type |
Description |
|
srid |
integer |
The unique identifier of the SRS. |
|
auth_name |
varchar(256) |
The name of the standard or standards body of the reference system. |
|
auth_srid |
integer |
The unique identifier of the reference system under its standard or standards body. |
|
srtext |
varchar(2048) |
The WKT representation of the SRS. |
|
proj4text |
varchar(2048) |
The PROJ4 representation of the SRS. |
In GanosBase, you can use the ST_SrReg function to register a new spatial reference and use the ST_SrEqual function to compare two spatial references.