units.xsd v3.0 draft last updated 2002/04/22 GML 3.0 candidate schema. Copyright (c) 2002 OGC, All Rights Reserved. This schema encodes the Coordinate Operations (CC_) package in the CRS UML Model. A mathematical operation on coordinates that transforms or converts coordinates to another coordinate reference system. Required number of dimensions in source CRS. Required number of dimensions in target CRS. Estimate of the impact of this coordinate operation on point position accuracy. Gives position error estimates for target coordinates of this coordinate operation, assuming no errors in source coordinates. Association to the source CRS (coordinate reference system) of this coordinate operation. Association to the target CRS (coordinate reference system) of this coordinate operation. See UML model for constraints on multiplicity of "sourceCRS" and "targetCRS". Association to a Coordinate Operation, either referencing or containing the definition of that Coordinate Operation. An ordered sequence of two or more simple coordinate operations. The sequence of operations is constrained by the requirement that the source coordinate reference system of step (n+1) must be the same as the target coordinate reference system of step (n). The source coordinate reference system of the first step and the target coordinate reference system of the last step are the source and target coordinate reference system associated with the concatenated operation. Association to a Simple Operation used by this concatenated operation. Association to a Concatenated Operation, either referencing or containing the definition of that Concatenated Operation. A simple (not concatenated) coordinate operation. Association to a Simple Operation, either referencing or containing the definition of that Simple Operation. A pass-through operation specifies that a subset of a coordinate tuple is subject to a specific coordinate operation. Ordered sequence of positive integers defining the positions in a coordinate tuple of the coordinates affected by this pass-through operation. Association to the operation applied to the specified ordinates. Association to a Pass Through Operation, either referencing or containing the definition of that Pass Through Operation. A parameterized mathematical operation on coordinates that transforms or converts coordinates to another coordinate reference system. This coordinate operation thus uses an operation method, usually with associated parameter values. Association to the operation method used by this operation. Composition of set of parameter values used by this operation. Association to an abstract Operation, either referencing or containing the definition of that Operation. A parameter value or reference to a file of parameter values. Numeric value of an operation parameter with its associated unit of measure. Reference to a file containing multiple parameter values, each with its associated unit of measure. Association to the operation parameter that this is a value of. An operation on coordinates that does not include any change of Datum. The best-known example of a coordinate conversion is a map projection. The parameters describing coordinate conversions are defined rather than empirically derived. Note that some conversions have no parameters. Association to a Conversion, either referencing or containing the definition of that Conversion. An operation on coordinates that usually includes a change of Datum. The parameters of a coordinate transformation are empirically derived from data containing the coordinates of a series of points in both coordinate reference systems. This computational process is usually "over-determined", allowing derivation of error (or accuracy) estimates for the transformation. Also, the stochastic nature of the parameters may result in multiple (different) versions of the same coordinate transformation. Association to a Transformation, either referencing or containing the definition of that Transformation. The definition of an algorithm used to perform a coordinate operation. Most operation methods use a number of operation parameters (although some coordinate conversions use none. Each coordinate operation using the method assigns values to all these parameters. Most parameter values are numeric, but other types of parameter values are possible. Formula(s) used by this operation method. The value may be a reference to a publication. Associations to the set of operation parameters used by this operation method. Association to an Operation Method, either referencing or containing the definition of that Operation Method. The definition of a parameter used by an operation method. Association to an Operation Parameter, either referencing or containing the definition of that Operation Parameter.