11.7.1 GIS Features That Are Not Yet Implemented

Additional Metadata Views

OpenGIS specifications propose several additional metadata views. For example, a system view named GEOMETRY_COLUMNS contains a description of geometry columns, one row for each geometry column in the database.

Functions to add/drop spatial columns

OpenGIS assumes that columns can be added or dropped using special AddGeometryColumn() and DropGeometryColumn() functions. In MySQL, this is done using the ALTER TABLE, CREATE INDEX, and DROP INDEX statements instead.

Factors related to Spatial Reference Systems and their IDs (SRIDs):

• Functions like Length() and Area() assume a planar coordinate system.
• All objects currently are considered to be in the same planar coordinate system.

The OpenGIS function Length() on LineString and MultiLineString currently should be called in MySQL as GLength()

The problem is that it conflicts with the existing SQL function Length() that calculates the length of string values, and sometimes it's not possible to distinguish whether the function is called in a textual or spatial context. We need either to solve this somehow, or decide on another function name.

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