AUTOCEN: Find the Center of an Extended Object

AUTOCEN attempts to find the center of an extended and possibly amorphous object by use of reflected autocorrelation. It is designed for objects like globular clusters. For smooth objects, the AXES command is better. The routine works by calculating a set of correlation amplitudes about an estimated image center. Amplitudes are measured on an N X N grid with sampling taken at STEP spacing in pixels. At each sample point the mean is calculated in a SIZE X SIZE pixel cell, and is subtracted in calculations of the autocorrelation amplitude, which is calculated by the product of the cell with its image reflected about its center. The default values for N, SIZE, and STEP are 7, 75, and 4. The final center is calculated by fitting a paraboloid to the grid of amplitudes. The results are saved in the VISTA variables AXR and AXC, and in the AXES common block. If the PLOT keyword is specified, a cross is marked at the determined center on the TV image.

See Also: AXES