Introduction Centering algorithms are important to many astronomical applications.
The required mathematics libraries are part of the IRAF core system MATH package. New centering and sky fitting algorithms can be added by writing the required low level routines, and making the appropriate entries in the algorithms. The following routines are examples of the 2-D numerical interface routines. The test field contained 500 stars uniformly distributed in position and in brightness over a 10 magnitude range. 2.5 was used to model the stars, and realistic Poisson and Gaussian read noise were added to the image.