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SLA_PXY - Apply Linear Model   

ACTION:
Given arrays of expected and measured $[\,x,y\,]$ 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 $[\,x,y\,]$ for each sample
XYM D(2,NP) measured $[\,x,y\,]$ for each sample
COEFFS D(6) coefficients of model (see below)

RETURNED:

XYP D(2,NP) predicted $[\,x,y\,]$ 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 $[x_{m},y_{m}\,]$ into predicted coordinates $[x_{p},y_{p}\,]$ as follows:
xp = a + bxm + cym
yp = d + exm + fym
2.
The residuals are (xp-xe) and (yp-ye).
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


next up previous
Next: SLA_RANDOM - Random Number
Up: SUBPROGRAM SPECIFICATIONS
Previous: SLA_PVOBS - Observatory Position & Velocity

SLALIB --- Positional Astronomy Library
Starlink User Note 67
P. T. Wallace
12 October 1999
E-mail:ptw@star.rl.ac.uk