Index: trunk/doc/modules/ModulesSDRS.tex =================================================================== --- trunk/doc/modules/ModulesSDRS.tex (revision 6757) +++ trunk/doc/modules/ModulesSDRS.tex (revision 6762) @@ -1,3 +1,3 @@ -%%% $Id: ModulesSDRS.tex,v 1.76 2006-04-01 03:07:09 price Exp $ +%%% $Id: ModulesSDRS.tex,v 1.77 2006-04-04 18:52:47 eugene Exp $ \documentclass[panstarrs,spec]{panstarrs} @@ -1851,34 +1851,120 @@ the fringe pattern is used both in the process of constructing the master image and in scaling the master image when it is applied to -science image. We thus need a method of measuring the fringe -amplitude which is robust in the presence of stars and which is fast. -We implement a method used at CFHT in which the fringe pattern is -mapped by a series of points pairs which correspond to peaks and -valleys of the fringe pattern. We define the following function to -measure the global fringe amplitude of an image given a collection of -fringe point pairs. -\begin{prototype} -stats *pmFringeStats (psArray *fringePoints, psImage *image, psMetadata *config); -\end{prototype} -This function measures the robust median at each of the minimum and -maximum coordinates and determines the difference and mean of the two -values. The size of the box used to make the measurement at each -point is specified by the configuration variable -\code{FRINGE_SQUARE_RADIUS}. From the collection of differences, the -robust median is calculated, and returned as part of the fringe -statistics. For each fringe point, the values of \code{delta} and -\code{midValue} are also assigned and available to the user on return. - -The \code{fringePoints} are defined by the following structure: +science image. This is the method currently in use at CFHT and it +usually performs well. However, the fringe signal can vary as the +emission lines in the atmosphere change, and the above method breaks +down unless different fringe images corresponding to different +atmospheric conditions are constructed. + +An alternative technique is to use multiple master fringe images at +the same time, each representing different atmospheric conditions. +The observed fringe frame can be considered as a linear combination of +different fringe patterns, depending on the relative strengths of the +lines active in creating each of the fringe masters. It is not +critical that the fringe master images represent completely orthogonal +fringe patterns, they need only sample sufficiently different +conditions to provide a handle on the underlying fringe signals. + +We define a method of measuring the fringe pattern which is robust in +the presence of stars and which is fast. We implement a varient on +the method used at CFHT in which the fringe pattern is mapped by a +series of points distributed across the image. At CFHT, manual effort +is used to carefully define point pairs which correspond to peaks and +valleys of the fringe pattern. We implement a different approach in +which the fringe points are randomly chosen across the image. At each +point in the image, the median flux is measured in a box of specified +size. A low-frequency spatial filter is then applied to these +measurements. The resulting array of points and fluxes then +represents the strength of the fringe pattern on that image. The +comparison between any two fringe images is then just a linear fit +between these fringe statistics vectors, as follows: +\[ +S_i = C_0 + C_1 F_i +\] +where $S_i$ is the fringe statistic on the science image and $F_i$ is +the fringe statistic on the reference fringe image. Extending this +logic to any number of reference fringe images results in the +following relationship: +\[ +S_i = C_0 + \sum_j C_j F_j +\] + +In order to correct a single science image, the collection of fringe +statistics ($S_i$) are used to measure the coefficients $C_0$, $C_j$. +The linear combination of the reference fringe images is then used to +build a master image which is subtracted from the science image. The +following structures and functions implement the above concepts. + +The \code{pmFringeStats} structure represents the fringe statistics +for a given image. \begin{datatype} typedef struct { - double xMin; - double yMin; - double xMax; - double yMax; - double delta; - double midValue; -} pmFringePoint; + psU32 nRequested; // number of fringe points selected + psU32 nAccepted; // number of fringe points not masked + psU32 dX; // median box half-width + psU32 dY; // median box half-height + psU32 nX; // large-scale smoothing in x (col) + psU32 nY; // large-scale smoothing in y (row) + psVector x; // fringe point coordinates (col) + psVector y; // fringe point coordinates (row) + psVector f; // fringe point median + psVector df; // fringe point stdev + psVector mask; // fringe point on/off mask +} pmFringeStats; \end{datatype} + +The \code{pmFringeStats} structure is allocated with the following +function: +\begin{prototype} +pmFringeStats *pmFringeStatsAlloc ( + int nPts, // number of points to create + int dX, // half-width of fringe boxes + int dY, // half-height of fringe boxes + int nX, // smoothing scale in x + int nY // smoothing scale in y +); +\end{prototype} + +A set of fringe points appropriate to the dimensions of a specific +image are created with the following function: +\begin{prototype} +bool pmFringeStatsCreatePoints (pmFringeStats *fringe, psImage *image); +\end{prototype} + +In general, \code{pmFringeStatsCreatePoints} should only be needed +when a new chip and filter are first use for analysis. Multiple +fringe images with the same chip and filter need to be examined with +the same fringe points in order for the statistical comparison to be +meaningful. The constructed fringe points should be saved and loaded +as a FITS table using the following function: +\begin{prototype} +bool pmFringeStatsWriteFits (psFits *fits, pmFringeStats *fringe); +bool pmFringeStatsReadFits (psFits *fits, pmFringeStats *fringe); +\end{prototype} + +In order to measure the fringe statistics for a given image, the +following function is defined: +\begin{prototype} +bool pmFringeStatsMeasure(pmFringeStats *fringe, pmReadout *readout) +\end{prototype} +This function measures the robust median at each of the fringe points +and saves the median values in \code{fringe->f} and the scatter in +\code{fringe->df}. + +Given the fringe statistics for a science image, and the fringe +statistics for a set of reference fringe images, the following +function can be used to measure the scaling coefficients of the +reference fringe frames which best fit the science image fringe +pattern: +\begin{prototype} +pmFringeScale *pmFringeScaleMeasure (pmFringeStats *science, psArray *fringes) +\end{prototype} + +Given a science image, a set of master fringe images, and a the set of +fringe statistics for the reference fringe images, the following +function can be used to correct the science image for the fringe pattern: +\begin{prototype} +psImage *pmFringeCorrect(psImage *out, psMetadata *info, psImage *science, psArray *fringeImage, psArray *fringeStats); +\end{prototype} \subsection{Flat-field Re-Normalization} @@ -2945,4 +3031,45 @@ available approximation to the Sextractor classification scheme. \tbd{the correspondence is not yet defined}. + +\subsection{Object List Input/Output} + +We support several object catalog formats. Some of these mimic the +formats used by the Elixir system to support testing with existing +data and software. Some of these are for use by the Pan-STARRS +project for testing. + +\subsubsection{OBJ Format} + +This format is produced by versions of DoPhot and is used by the +Elixir system as an intermediate output data product. The objects are +written to a text file with fixed line-length and with fixed column +positions. The file has no header associated with it. This is only +an output format, and should be used just for testing and comparison +with the Elixir tools. + +\subsubsection{SX Format} + +This format is produced by versions of Sextractor and is used by the +Elixir system as an intermediate output data product. The objects are +written to a text file with fixed line-length and with fixed column +positions. The file has no header associated with it. This is only +an output format, and should be used just for testing and comparison +with the Elixir tools. The SX and OBJ formats are similar, but use a +somewhat different definition of the columns. + +\subsubsection{CMP Format} + +This format is used extensively by the Elixir system, and many data +files are available in this format. The format is a pseudo-FITS +format, consisting of a FITS header (with NAXIS=2) and a text data +segment with fixed line length. The CMP files are always in SPLIT +format in the sense that each object table is a single file. + +\subsubsection{CMF Format} + +This format is a true FITS table format. The object data is stored +for each readout in a separate extension. In addition, the Cell +headers are stored in their own extensions (with NAXIS=0). In SPLIT +format, the Cell header is the PHU header. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%