ppos measures the positions of peaks in a collapsed Ultracam data files, i.e. files produced by the program collapse. These are frames in which all the windows have been collpased in either X or Y so that they are cross-cuts of a frame. ppos measures the positions of these using cross-correlation with a gaussian. This will grind through each window. Peaks will be reported in left-to-right or bottom-to-top order within a given window. When the position of a local maximum is measured by cross-correlation is will lock onto the most significant peak within ~FWHM of the starting position. This can mean that multiple local maxima will lead to the same final position. Therefore the routines has an option to skip peaks with the same position as the previous one if it is not sufficiently far away.
ppos data nccd fwhm height gain minsep
|data||---||An Ultracam data file from collapse. All windows must be 1D or null.|
|nccd||---||The particular CCD to measure|
|fwhm||---||The full width half-maximum of the gaussian in pixels to use for cross-correlation. Note that this is measured in binned pixels and must be at least 2|
|height||---||Minimum height above the background (measured from the median) for a peak to be included.|
|gain||---||Number of photons/ADU to estimate the uncertainties; an uncertainty for the background will be estimated from the difference between the the 16 and 50th perecentiles|
|minsep||---||Minimum separation of peaks to be reported in terms of a multiple of the FWHM. This prevents identical peaks being reported.|
collapse, expand, lplot
This command is a member of the classes: Programs, Spectra.
Author: T.R. Marsh
Created: 19 November 2006
Revised: 02 December 2006