casacore
measures
TableMeasures.h
Go to the documentation of this file.
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
42
namespace
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
casacore
this file contains all the compiler specific defines
Definition:
mainpage.dox:28
Generated by
1.8.18