On Thursday, the latest major release of PostGIS came out: version 1.5.  This release adds a long-wished-for feature to the open source spatial database—direct support for “geodetic” coordinates.

Geodetics are more commonly known as “lat/lon” coordinates. While you could load and work with lat/lon coordinates in earlier versions of PostGIS, the indexing and calculation code did not make any allowance for the fact that the coordinates were angular units, not cartesian units. As a result, objects that crossed the poles or datelines would not index properly, and calculations of areas, lengths and distances returned strange looking answers in “degrees” rather than meters.

With PostGIS 1.5, the new “geography” type is a 100% sphere-aware type, which can be indexed globally and returns answers in meters, using calculations on the spheroid for maximum correctness. It is built on top of a new disk storage and index format, which the existing “geometry” type will also transition to in version 2.0.

The development of the “geography” type was funded as a PostGIS core development task, by a company that chooses to remain anonymous.  Since the main geography development is complete the old task has been updated to a new version, outlining extra functions and performance additions that could be added to geography support.

We expect that the geography type will make it easier for new users to store their data in PostGIS (without having to learn about projections and coordinate systems before starting) and also allow global data managers to store and query international data sets for effectively.

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