**ACTION:**- Given arrays of
*expected*and*measured*coordinates, and a linear model relating them (as produced by sla_FITXY), compute the array of*predicted*coordinates and the RMS residuals. **CALL:**`CALL sla_PXY (NP,XYE,XYM,COEFFS,XYP,XRMS,YRMS,RRMS)`

**GIVEN:**-

*NP***I**number of samples *XYE***D(2,NP)**expected for each sample *XYM***D(2,NP)**measured for each sample *COEFFS***D(6)**coefficients of model (see below)

**RETURNED:**-

*XYP***D(2,NP)**predicted for each sample *XRMS***D**RMS in X *YRMS***D**RMS in Y *RRMS***D**total RMS (vector sum of XRMS and YRMS)

**NOTES:**- 1.
- The model is supplied in the array COEFFS. Naming the
six elements of COEFFS
*a*,*b*,*c*,*d*,*e*&*f*, the model transforms*measured*coordinates into*predicted*coordinates as follows:*x*_{p}=*a*+*bx*_{m}+*cy*_{m}

*y*_{p}=*d*+*ex*_{m}+*fy*_{m} - 2.
- The residuals are (
*x*_{p}-*x*_{e}) and (*y*_{p}-*y*_{e}). - 3.
- If NP is less than or equal to zero, no coordinates are transformed, and the RMS residuals are all zero.
- 4.
- See also sla_FITXY, sla_INVF, sla_XY2XY, sla_DCMPF

Starlink User Note 67

P. T. Wallace

12 October 1999

E-mail:ptw@star.rl.ac.uk