<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<!--Converted with LaTeX2HTML 98.1p1 release (March 2nd, 1998)
originally by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds
* revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan
* with significant contributions from:
Jens Lippmann, Marek Rouchal, Martin Wilck and others -->
<HTML>
<HEAD>
<TITLE>MIDAS Data Structures</TITLE>
<META NAME="description" CONTENT="MIDAS Data Structures">
<META NAME="keywords" CONTENT="vol1">
<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
<LINK REL="STYLESHEET" HREF="vol1.css">
<LINK REL="next" HREF="node31.html">
<LINK REL="previous" HREF="node24.html">
<LINK REL="up" HREF="node22.html">
<LINK REL="next" HREF="node26.html">
</HEAD>
<BODY >
<!--Navigation Panel-->
<A NAME="tex2html795"
HREF="node26.html">
<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next"
SRC="icons.gif/next_motif.gif"></A>
<A NAME="tex2html791"
HREF="node22.html">
<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up"
SRC="icons.gif/up_motif.gif"></A>
<A NAME="tex2html785"
HREF="node24.html">
<IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous"
SRC="icons.gif/previous_motif.gif"></A>
<A NAME="tex2html793"
HREF="node1.html">
<IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents"
SRC="icons.gif/contents_motif.gif"></A>
<A NAME="tex2html794"
HREF="node216.html">
<IMG WIDTH="43" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="index"
SRC="icons.gif/index_motif.gif"></A>
<BR>
<B> Next:</B> <A NAME="tex2html796"
HREF="node26.html">Specifying a Descriptor</A>
<B> Up:</B> <A NAME="tex2html792"
HREF="node22.html">Monitor and Command Language</A>
<B> Previous:</B> <A NAME="tex2html786"
HREF="node24.html">MIDAS And the Host</A>
<BR>
<BR>
<!--End of Navigation Panel-->
<H1><A NAME="SECTION00630000000000000000"> </A> <A NAME="1421"> </A>
<A NAME="midas-data-structures"> </A>
<BR>
MIDAS Data Structures
</H1>
<P>
Here we describe and discuss the various data entities (structures)
that MIDAS recognizes.
They are stored in an internal binary format,
accessible only through MIDAS and fall into the following categories:
<BR><DL COMPACT><DT>Images
<DD><A NAME="1424"> </A> are a set of data of same physical significance
in one to three dimensions. The data must be sampled with constant
step size along all 1, 2 or 3 axes and are stored in different formates,
e.g., as bytes,
16 bit integers, or 32 bit reals on disk. However, most MIDAS
applications work on real data, so the image pixels are converted on the fly
to real format if necessary.
The default file type is <TT>.bdf</TT> .
<BR>
Besides the internal binary format also images in FITS format are supported
by all Midas applications.
<DT>Tables
<DD><A NAME="1426"> </A> are a structure for handling data which can be arranged
in rows and columns. The data may be of numerical or character type.
Numerical data may be sampled in any arbitrary fashion.
The default file type is <TT>.tbl</TT> .
<DT>Fit-files
<DD><A NAME="1428"> </A> are ``degenerate'' image files with just descriptors and
no pixels and
used to store the parameters needed for the fitting functions.
The default file type is <TT>.fit</TT> .
<DT>Descriptors
<DD><A NAME="1430"> </A> are variables attached to the structures mentioned
above (i.e. stored in the same file) and describe the structure of
the tables, images and fit files. They can also store any other
auxiliary information connected to the data such as histograms,
coordinates, comments and so on. For fit files they contain the fitting
parameters.
<BR>
The Midas descriptors are the equivalent of the FITS header keywords.
<DT>Catalogs
<DD><A NAME="1431"> </A> contain lists of either images or tables or fit files
for the purpose of grouping data together within MIDAS.
They are exceptional in the sense that they are implemented as ASCII
files so you can list and edit them (with care!) outside MIDAS.
The default file type is <TT>.cat</TT> .
<DT>Keywords
<DD><A NAME="1433"> </A> are variables which can be used to pass information
from one MIDAS program to the next or to temporarily store intermediate
results (there are also <I>reserved</I> or <I>system</I> keywords that keep
MIDAS system
parameters). They are referred to by a name and can be easily manipulated
from the terminal or MIDAS procedures. </DL> <BR>
The individual data points in an image are referred to as ``pixels''<A NAME="1437"> </A>
and in a table they are called ``elements''<A NAME="1438"> </A>. The paragraphs
below describe the structure of descriptors, and keywords, and
the methods for specifying the individual data values in images
and tables.
<P>
<BLOCKQUOTE>
<DIV ALIGN="CENTER">
<B>Note</DIV>
<I>There is no special syntax for file names in MIDAS. You can use any
legal name of your host file system for images, tables and fit files.
However, a name beginning with a digit or using any of the characters
<BR>
+, -, *, /, `, !, </I></B>|<B><I>, ( and ),
should be avoided, because these symbols will cause problems in e.g. the
<TT>COMPUTE/IMAGE</TT> command.
If you do want to use a file name with these special characters in a
<TT>COMPUTE/IMAGE</TT> command you have to enclose the full name (including the
file type) in quotes, i.e.
<BR>
<TT>Midas 456> COMPUTE/IMAGE res = 12 </TT></I></B>+<B><I><TT> "quasar01</TT></I></B>+<B><I><TT>12.bdf"</TT>
</I></B>
<P>
<B><I>The length of these names is, in principle, limited to 60 characters for
MIDAS applications (which used to be the size of keywords IN_A, OUT_A,
employed in most procedures to store the image, table names...).
However, via the <TT>SET/MIDAS dpath=</TT> command you can specify other
directories which are scanned for data files besides the current directory.
</I></B>
<P>
<B><I>Also file names like <TT>abc.bdf.mine</TT>
will not be appreciated by all MIDAS applications.
<BR>
As mentioned before, file names are case sensitive in MIDAS on Unix systems;
names for descriptors and keywords are not. Thus, referring to a keyword with
name <TT>KEYA</TT> may be done e.g. via <TT>keyA</TT> or <TT>Keya</TT>.</I></B></BLOCKQUOTE>
<P>
<BR><HR>
<!--Table of Child-Links-->
<A NAME="CHILD_LINKS"> </A>
<UL>
<LI><A NAME="tex2html797"
HREF="node26.html">Specifying a Descriptor</A>
<LI><A NAME="tex2html798"
HREF="node27.html">Specifying Keywords</A>
<LI><A NAME="tex2html799"
HREF="node28.html">Specifying Elements in a Table</A>
<LI><A NAME="tex2html800"
HREF="node29.html">Specifying Pixels in an Image</A>
<LI><A NAME="tex2html801"
HREF="node30.html">Specifying Sub-Image</A>
</UL>
<!--End of Table of Child-Links-->
<HR>
<!--Navigation Panel-->
<A NAME="tex2html795"
HREF="node26.html">
<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next"
SRC="icons.gif/next_motif.gif"></A>
<A NAME="tex2html791"
HREF="node22.html">
<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up"
SRC="icons.gif/up_motif.gif"></A>
<A NAME="tex2html785"
HREF="node24.html">
<IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous"
SRC="icons.gif/previous_motif.gif"></A>
<A NAME="tex2html793"
HREF="node1.html">
<IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents"
SRC="icons.gif/contents_motif.gif"></A>
<A NAME="tex2html794"
HREF="node216.html">
<IMG WIDTH="43" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="index"
SRC="icons.gif/index_motif.gif"></A>
<BR>
<B> Next:</B> <A NAME="tex2html796"
HREF="node26.html">Specifying a Descriptor</A>
<B> Up:</B> <A NAME="tex2html792"
HREF="node22.html">Monitor and Command Language</A>
<B> Previous:</B> <A NAME="tex2html786"
HREF="node24.html">MIDAS And the Host</A>
<!--End of Navigation Panel-->
<ADDRESS>
<I>Petra Nass</I>
<BR><I>1999-06-09</I>
</ADDRESS>
</BODY>
</HTML>
