Geographic features can be measured in degrees of latitude, radians, or other angular units of measure. Every spatial reference system must explicitly state the name of the unit in which geographic coordinates are measured, and must include the conversion from the specified unit to a radian.
If you are using a projected coordinate system, the individual coordinate values represent a linear distance along the surface of the Earth to a point. Coordinate values can be measured by the meter, foot, mile, or yard. The projected coordinate system must explicitly state the linear unit of measure in which the coordinate values are expressed.
The following units of measure are automatically installed in any new SQL Anywhere database:
meter A linear unit of measure. Also known as International metre. SI standard unit. Defined by ISO 1000.
metre A linear unit of measure. An alias for meter. SI standard unit. Defined by ISO 1000.
radian An angular unit of measure. SI standard unit. Defined by ISO 1000:1992.
degree An angular unit of measure (pi()/180.0 radians).
planar degree A linear unit of measure. Defined as 60 nautical miles. A linear unit of measure used for geographic spatial reference systems with PLANAR line interpretation.
Discuter à propos de cette page dans DocCommentXchange.
|Copyright © 2010, iAnywhere Solutions, Inc. - SQL Anywhere 12.0.0|