Transforming 2-Dimensional Coordinate Data

Transformations which inter-relate 2-dimensional coordinate systems are common in graphical and image-processing applications, so a set of routines is provided for applying the associated { $2 \rightarrow 2$} mappings to coordinate data. These routines have names of the form TRN_TR2x, where x is either I, R or D according to whether the data are specified by integer, real or double precision values respectively. Thus, to apply a compiled { $2 \rightarrow 2$} mapping to a set of 2-dimensional data points specified by two lists of real coordinates $X_{IN}$ and $Y_{IN}$, the following statement might be used:

CALL TRN_TR2R( BAD, NXY, XIN, YIN, ID, XOUT, YOUT, STATUS )

where:

• BAD is a logical value specifying whether the input coordinates may contain bad values (see Section );

• NXY specifies the number of data points to be transformed;

• XIN and YIN are 1-dimensional arrays containing the $X_{IN}$ and $Y_{IN}$ coordinates of the input data points;

• ID is an identifier associated with the compiled { $2 \rightarrow 2$} mapping to be applied;

• XOUT and YOUT are 1-dimensional arrays to receive the (transformed) $X_{OUT}$ and $Y_{OUT}$ coordinates of the output data points;

• STATUS is an inherited error status variable.