Index: /trunk/doc/config/config.tex
===================================================================
--- /trunk/doc/config/config.tex	(revision 9677)
+++ /trunk/doc/config/config.tex	(revision 9678)
@@ -1,3 +1,3 @@
-%%% $Id: config.tex,v 1.2 2006-10-20 03:51:59 price Exp $
+%%% $Id: config.tex,v 1.3 2006-10-20 22:07:17 price Exp $
 \documentclass[panstarrs,spec]{panstarrs}
 
@@ -230,4 +230,15 @@
 
 \section{Camera configuration}
+
+The Focal Plane hierarchy (\code{pmFPA, pmChip, pmCell, pmReadout}) is
+explained in more detail in \S\ref{sec:focalplane}.  The top level, an
+FPA, contains one or more chips, which correspond to a contiguous piece
+of silicon.  A chip contains one or more cells, which correspond to a
+single amplifier.  A cell contains one or more readouts, which
+correspond to individual reads of the detector.
+
+The purpose of the camera configuration is to define the contents of
+the Focal Plane hierarchy, and to define parameters that are
+particular to the camera.
 
 \subsection{Location}
@@ -485,4 +496,22 @@
 \section{Camera format configuration}
 
+The FITS data storage formation is a standard in the astronomical
+community for storing astronomical images.  A FITS file consists of an
+arbitrary number of coupled human readable \code{ASCII} header
+segments and binary data segments.  The headers describe the format
+and layout of the data segments.  The first of these groups is
+traditionally called the ``primary header unit'' (PHU) and the rest
+are referred to as ``extensions''.  The header segments may contain
+extensive documentary information related to the interpretation of the
+data.  Although the FITS format defines a standard representation of
+the data, the header metadata is not so consistently defined within
+the astronomical community.  Also, the flexibility of the data format
+means that different representations are possible for the same
+fundamental collection of data.
+
+The purpose of the camera format file is to define how FITS files are
+to be read into the Focal Plane hierarchy, and how the ``concepts''
+are to be ingested.
+
 \subsection{Location}
 
@@ -517,4 +546,25 @@
 
 \subsubsection{How to read the file}
+
+Within the FITS data representation, there are various choices which
+can and have been made for the placement of the pixels in the file.
+In the simplest case, the camera consists of a single chip consisting
+of a single cell always read with a single readout.  In this case, the
+image data could be written as part of the primary header unit.  In a
+more complex case with multiple chips and multiple cells, the data may
+be organized in several ways.  The data may be distributed into
+multiple files or in multiple FITS data extensions.  A single camera
+image may be written as a collection of files for individual chips
+with separate extensions for each cell (CFH12K.split, GPC).  Another
+camera may write a single file with multiple extensions for each cell
+(Megacam.raw), or multiple extensions per chip, with each cell
+representing portions of the chip image (Megacam.splice, CFHT-IR).
+
+In all of these representations, there are only two basic distinctions
+in how the pixel data is stored: what level in the hierarchy the
+entire FITS file corresponds to (FPA, chip, or cell), and what level
+the extensions correspond to (chip, cell or no extensions at all).
+Knowing these, and having a list of the extensions, we can construct
+the Focal Plane hierarchy.
 
 \code{FILE(METADATA)} contains information on how to read the FITS