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TableMeasures.h
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1//# TableMeasures.h: Create Measure and Quantum columns Tables.
2//# Copyright (C) 1996,1997,1998,1999,2000,2001
3//# Associated Universities, Inc. Washington DC, USA.
4//#
5//# This library is free software; you can redistribute it and/or modify it
6//# under the terms of the GNU Library General Public License as published by
7//# the Free Software Foundation; either version 2 of the License, or (at your
8//# option) any later version.
9//#
10//# This library is distributed in the hope that it will be useful, but WITHOUT
11//# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12//# FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public
13//# License for more details.
14//#
15//# You should have received a copy of the GNU Library General Public License
16//# along with this library; if not, write to the Free Software Foundation,
17//# Inc., 675 Massachusetts Ave, Cambridge, MA 02139, USA.
18//#
19//# Correspondence concerning AIPS++ should be addressed as follows:
20//# Internet email: aips2-request@nrao.edu.
21//# Postal address: AIPS++ Project Office
22//# National Radio Astronomy Observatory
23//# 520 Edgemont Road
24//# Charlottesville, VA 22903-2475 USA
25//#
26//# $Id$
27
28#ifndef MEASURES_TABLEMEASURES_H
29#define MEASURES_TABLEMEASURES_H
30
31#include <casacore/casa/aips.h>
32#include <casacore/measures/TableMeasures/ArrayMeasColumn.h>
33#include <casacore/measures/TableMeasures/ArrayQuantColumn.h>
34#include <casacore/measures/TableMeasures/ScalarMeasColumn.h>
35#include <casacore/measures/TableMeasures/ScalarQuantColumn.h>
36#include <casacore/measures/TableMeasures/TableMeasDesc.h>
37#include <casacore/measures/TableMeasures/TableMeasOffsetDesc.h>
38#include <casacore/measures/TableMeasures/TableMeasRefDesc.h>
39#include <casacore/measures/TableMeasures/TableMeasValueDesc.h>
40#include <casacore/measures/TableMeasures/TableQuantumDesc.h>
41
42namespace casacore { //# NAMESPACE CASACORE - BEGIN
43
44// <module>
45
46// <summary>
47// Create and use scalar and array columns of Quanta and Measures in Tables.
48// </summary>
49
50// <prerequisite>
51// <li> <linkto module=Measures>Measures</linkto>
52// <li> <linkto module=Tables>Tables</linkto>
53// </prerequisite>
54
55// <reviewed reviewer="Bob Garwood" date="1999/12/23">
56// </reviewed>
57
58// <etymology>
59// Table columns containing Measures and Quanta
60// </etymology>
61
62// <synopsis>
63
64// The TableMeasures system exists to provide a way of creating (defining)
65// Measure and Quantum Table columns thus enabling the direct storage of
66// Quanta and Measures in Casacore Tables.
67// <p>
68// Defining Quantum and Measure columns is a once only operation (for each
69// column). It can be seen as an extension to the existing Column Descriptor
70// mechanism which adds a column of a specified type to a table. The
71// <linkto><class=TableMeasDesc>TableMeasDesc</linkto> and
72// <linkto><class=TableQuantumDesc>TableQuantumDesc</linkto> class
73// hierarchies are used to define Measure and Quantum columns.
74// <p>
75// Once defined, Measure and Quantum column objects are used to access a
76// column for reading and writing of Measures and Quanta. For Quantum
77// column objects see the class
78// <linkto><class=ScalarQuantColumn>ScalarQuantColumn</linkto> and
79// <linkto><class=ArrayQuantColumn>ArrayQuantColumn</linkto>. For
80// Measure column objects see
81// <linkto><class=ScalarMeasColumn>ScalarMeasColumn</linkto> and
82// <linkto><class=ArrayMeasColumn>ArrayMeasColumn</linkto>.
83//
84// <h3>Conversions</h3>
85// The classes accessing the data use the underlying
86// <linkto module=Quanta>Quanta</linkto> or
87// <linkto module=Measures>Measures</linkto> classes to convert
88// the units or references of the measures or quanta.
89// The TableMeasures classes do not test if a conversion is possible.
90// <br>In general one can say that about every unit conversion is possible.
91// The <linkto class=Unit>Unit</linkto> class adjusts units as needed.
92// <br>Conversions of Measures are only possible if enough information
93// is supplied for the measure's reference.
94// <br>Take a look at the abovementioned modules to find out about conversions.
95//
96// <h3>Performance</h3>
97// Using the TableMeasures classes makes it easier to deal with
98// measures in tables. However, there is a performance penalty
99// compared to handling the values directly in the table using
100// the Tables classes <linkto class=ScalarColumn>ScalarColumn</linkto>
101// and <linkto class=ArrayColumn>ArrayColumn</linkto>.
102//
103// The performance of the TableMeasures classes depends on how the
104// measures are stored; thus if a fixed or variable offset and reference
105// are used.
106// Of course, it also depends on whether the measures have to be
107// converted before they can be stored.
108// <br>The TableMeasures classes are always slower than the Tables classes,
109// but they offer more convenience.
110// In general one can say that for large tables it is better to use
111// the Tables classes directly to put/get the data.
112// However, even when putting directly using the Tables classes, the
113// column itself should be defined as a TableMeasure. In that way there
114// is one standard way of defining columns as table measures.
115// <br>For example, the TIME column in a MeasurementSet should be handled
116// directly uisng the Tables classes (because it is so large).
117// On the other hand, the FIELD table is very small and it may make life
118// easier to handle its columns through the TableMeasures classes.
119//
120// In a test putting an array of quanta using class
121// <linkto class=ArrayQuantColumn>ArrayQuantColumn</linkto> took
122// about 5 times as long as doing it directly using class
123// <linkto class=ArrayColumn>ArrayColumn</linkto>. The quantum column
124// had variable units. so for each row the unit had to be written as well.
125// Reading it back took about 3 times as long.
126// <br>When using a qunatum column with fixed units, putting took about
127// 2.5 times as long as using <src>ArrayColumn</src> directly.
128// Each put involved a unit conversion.
129// Reading it back took only 10% more than when using <src>ArrayColumn</src>.
130//
131// </synopsis>
132
133// <motivation>
134// The standard Casacore Table system does not directly support Quantum and
135// Measure columns. These classes overcome this limitation.
136// </motivation>
137
138//# <todo asof="">
139//# </todo>
140
141// </module>
142
143
144} //# NAMESPACE CASACORE - END
145
146#endif
this file contains all the compiler specific defines
Definition mainpage.dox:28