TableQuantumDesc.h

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00001 //# TableQuantumDesc.h: Defines a Quantum column in a Table.
00002 //# Copyright (C) 1997,1998,1999,2000,2001
00003 //# Associated Universities, Inc. Washington DC, USA.
00004 //#
00005 //# This library is free software; you can redistribute it and/or modify it
00006 //# under the terms of the GNU Library General Public License as published by
00007 //# the Free Software Foundation; either version 2 of the License, or (at your
00008 //# option) any later version.
00009 //#
00010 //# This library is distributed in the hope that it will be useful, but WITHOUT
00011 //# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
00012 //# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
00013 //# License for more details.
00014 //#
00015 //# You should have received a copy of the GNU Library General Public License
00016 //# along with this library; if not, write to the Free Software Foundation,
00017 //# Inc., 675 Massachusetts Ave, Cambridge, MA 02139, USA.
00018 //#
00019 //# Correspondence concerning AIPS++ should be addressed as follows:
00020 //#        Internet email: aips2-request@nrao.edu.
00021 //#        Postal address: AIPS++ Project Office
00022 //#                        National Radio Astronomy Observatory
00023 //#                        520 Edgemont Road
00024 //#                        Charlottesville, VA 22903-2475 USA
00025 //#
00026 //# $Id$
00027 
00028 #ifndef MEASURES_TABLEQUANTUMDESC_H
00029 #define MEASURES_TABLEQUANTUMDESC_H
00030 
00031 //# Includes
00032 #include <casacore/casa/aips.h>
00033 #include <casacore/casa/Arrays/Vector.h>
00034 #include <casacore/casa/BasicSL/String.h>
00035 
00036 namespace casacore { //# NAMESPACE CASACORE - BEGIN
00037 
00038 //# Forward Declarations
00039 class TableDesc;
00040 class Table;
00041 class TableRecord;
00042 class TableColumn;
00043 class Unit;
00044 
00045 
00046 // <summary>
00047 // A class for defining Quantum columns in Tables.
00048 // </summary>
00049 
00050 // <use visibility=export>
00051 
00052 // <reviewed reviewer="Bob Garwood" date="1999/12/23" tests="tTableQuantum.cc">
00053 // </reviewed>
00054 
00055 // <prerequisite>
00056 //# Classes you should understand before using this one.
00057 //   <li> <linkto class=Table>Table</linkto>
00058 //   <li> <linkto class=Quantum>Quantum</linkto>
00059 // </prerequisite>
00060 
00061 // <synopsis>
00062 // A TableQuantumDesc object is used to define a Quantum column in a Table.
00063 // The use of this object and the associated Scalar- and ArrayQuantColumn
00064 // objects make it possible to store (and retrieve) Quanta in Tables.<br>
00065 //
00066 // TableQuantumDesc objects are analogous to ColumnDesc objects in that they
00067 // add information, describing the characteristics of a column, to the Table
00068 // Descriptor before the Table is created.  However, rather than
00069 // replacing the use of a ColumnDesc object, a TableQuantumDesc is
00070 // used in conjunction with a ColumnDesc in the definition of
00071 // Quantum columns.<br>
00072 //
00073 //   <note role=caution>
00074 //      A good understanding of the Table system is essential
00075 //      before attempting to use this class.
00076 //   </note>
00077 //
00078 // Defining a Quantum column requires the following steps:
00079 // <ol>
00080 // <li> Use a normal Scalar- or ArrayColumnDesc to define a column to use for
00081 //      the Quanta.
00082 // <li> If needed (see
00083 //      <A HREF="#TableQuantumDesc:Quantum Units">below</A>) define a column
00084 //      for the Quantum Units.
00085 // <li> Add the columns to the Table Descriptor.
00086 // <li> Declare a TableQuantumDesc to associate the column defined in step 1
00087 //      and the Unit column from step 2 and update the Table Descriptor.
00088 // <li> Setup and create the Table.
00089 // </ol>
00090 // It is also possible to define a Quantum column after the table is created.
00091 // which is useful when columns (to be used for quanta) are added to
00092 // an already existing table. <br>
00093 //
00094 // The type of the quantum columns must match the type of the underlying
00095 // Quanta that are to be stored in the column.  Hence, for a column of
00096 // Quantum&lt;Complex&gt; a ScalarColumnDesc&lt;Complex&gt; must be used.<br>
00097 //
00098 // As with standard Table Columns Quanta can be stored in Scalar and Array
00099 // columns. This must be specified in advance by using either a
00100 // Scalar- or ArrayColumnDesc.<br>
00101 //
00102 // After the Table has be created a Quantum column can be accessed for writing
00103 // and reading of Quanta via the
00104 // <linkto class="ScalarQuantColumn">(RO)ScalarQuantColumn&lt;T&gt;</linkto>
00105 // and
00106 // <linkto class="ArrayQuantColumn">(RO)ArrayQuantColumn&lt;T&gt;</linkto>
00107 // objects.
00108 //
00109 // <ANCHOR NAME="TableQuantumDesc:Quantum Units">
00110 // <h3>Quantum Units</h3></ANCHOR>
00111 // The treatment of the Unit component of a Quantum in the TableQuantumDesc
00112 // class varies depending on your needs.    The main consideration
00113 // is whether the Quanta to be stored in a specific column are to have the
00114 // same Unit or whether their Units could differ.  In the simple case,
00115 // where the
00116 // Quanta have the same unit, a TableQuantumDesc is declared with the
00117 // Unit value specified as a parameter. The following defines a Quantum
00118 // column with units "deg":
00119 //
00120 // <srcblock>
00121 //      ScalarColumnDesc<Double> scd("QuantumCol");
00122 //      ...
00123 //      // defines QuantumCol as a Quantum column with fix Units "deg"
00124 //      TableQuantumDesc tqd(td, "QuantumCol", Unit("deg"));
00125 // </srcblock>
00126 //
00127 // This constructor stores the value for the Unit as a
00128 // column keyword.  In situations, however, where it is necessary to
00129 // store a distinct Unit with each Quantum, it is necessary to define
00130 // an additional column for storing the Unit component of each Quantum.
00131 // The TableQuantumDesc constructor for this takes the name of
00132 // the Unit column as
00133 // a parameter.  Hence an additional column must be defined for storing the
00134 // Units and its type must be string.  The following
00135 // example shows how to set up a Quantum column with support for Quantum
00136 // unit variability:
00137 //
00138 // <srcblock>
00139 //      // the quanta values stored here
00140 //      ScalarColumnDesc<Double> scd("QuantumCol");
00141 //      // a String column for the Units
00142 //      ScalarColumnDesc<String> scd("QuantumUnitCol");
00143 //      ...
00144 //      TableQuantumDesc tqd(td, "QuantumCol", "QuantumUnitCol");
00145 // </srcblock>
00146 //
00147 // One further consideration is that for Array Quantum Columns it is
00148 // necessary to
00149 // decide on a level of granularity for the Unit storage you would like.
00150 // In Array Quantum columns it is possible to store a distinct Unit per row or
00151 // per array element per row.  This distinction is established when the
00152 // Unit column is declared.  Defining a ScalarColumn for Units specifies per
00153 // row variability, that is, each row in an array column of Quanta will
00154 // have the same unit.  Alternatively, use of an ArrayColumn for the Unit
00155 // column
00156 // specifies that every Quantum stored will have its unit stored as well.
00157 // In both cases the Unit column's type must be String.  The following
00158 // defines an Array Quantum Column with per row Unit storage:
00159 //
00160 // <srcblock>
00161 //      // for the Quanta values
00162 //      ArrayColumnDesc<Double> scd("ArrayQuantumCol");
00163 //      // per row storage of units
00164 //      ScalarColumnDesc<String> scd("QuantumUnitCol");
00165 //      ...
00166 //      TableQuantumDesc tqd(td, "ArrayQuantumCol", "QuantumUnitCol");
00167 // </srcblock>
00168 //
00169 // And finally, an array Quantum Column with an Array Unit Column:
00170 //
00171 // <srcblock>
00172 //      // for Quanta values
00173 //      ArrayColumnDesc<Double> scd("ArrayQuantumCol");
00174 //      // per element storage of Units
00175 //      ArrayColumnDesc<String> scd("ArrayUnitCol");
00176 //      ...
00177 //      TableQuantumDesc tqd(td, "ArrayQuantumCol", "ArrayUnitCol");
00178 // </srcblock>
00179 //
00180 //
00181 // After constructing an TableQuantumDesc object use of the write() member
00182 // updates the Table Descriptor or Table object.
00183 // <linkto class="ScalarQuantColumn">(RO)ScalarQuantColumn&lt;T&gt;</linkto>
00184 // and
00185 // <linkto class="ArrayQuantColumn">(RO)ArrayQuantColumn&lt;T&gt;</linkto>
00186 // are subsequently used to read-only and read/write access the Quantum
00187 // Columns.
00188 // </synopsis>
00189 //
00190 // <example>
00191 // <srcblock>
00192 //     // create a table descriptor as normal
00193 //     TableDesc td("measTD", "1", TableDesc::New);
00194 //     td.comment() = "A table containing measures and quantums";
00195 //
00196 //     // This example sets up a Quantum<Complex> column but any valid Quantum
00197 //     // type can be specified.  However, the type of the Quantums to be
00198 //     // stored must match the type of the underlying table column.
00199 //     ScalarColumnDesc<Complex> tcdQCplx("Quant", "A quantum complex column");
00200 //
00201 //     // For a Quantum array column an ArrayColumnDesc is first defined
00202 //     ArrayColumnDesc<Double> tcdQDoub("QuantArray", "A quantum array col");
00203 //
00204 //     // The QuantumArray column has variable units.  A string is needed
00205 //     // for these.  This could be done in two ways depending on what is
00206 //     // wanted.  Units can vary per element of array per row or
00207 //     // just per row.  In the first instance an ArrayColumn<String> would be
00208 //     // require.  Here we want to vary units only per row.
00209 //     ScalarColumnDesc<String> tcdUnits("VarQuantUnits", "Quantum units");
00210 //
00211 //     // Add the columns to the Table Descriptor
00212 //     td.addColumn(tcdQplx);
00213 //     td.addColumn(tcdQDoub);
00214 //     td.addColumn(tcdUnits);
00215 //
00216 //     // Create the TableQuantumDesc with units "deg" and an Array Quantum
00217 //     // Column with per row Unit granularity
00218 //     TableQuantumDesc tqdS(td, "Quant", unit("deg"));
00219 //     TableQuantumDesc tqdA(td, "QuantArray", "VarQuantUnits");
00220 //
00221 //     // Update the Table Descriptor
00222 //     tqdA.write(td);
00223 //     tqdS.write(td);
00224 //
00225 //     // Setup and create the new table as usual.
00226 //     SetupNewTable newtab("mtab", td, Table::New);
00227 //     Table qtab(newtab);
00228 //
00229 //     // Now ScalarQuantColumn and ArrayQuantColumn objects could be
00230 //     // constructed to access the columns...
00231 // </srcblock>
00232 // Note that writing the Quantum description could also be done
00233 // after the table is created. It is meaningless in this case, but
00234 // it is useful when columns (to be used for quanta) are added to
00235 // an already existing table.
00236 // be used as 
00237 // <srcblock>
00238 //     // Setup and create the new table as usual.
00239 //     SetupNewTable newtab("mtab", td, Table::New);
00240 //     Table qtab(newtab);
00241 //
00242 //     // Update the Table Descriptor
00243 //     tqdA.write(qtab);
00244 //     tqdS.write(qtab);
00245 // </srcblock>
00246 // </example>
00247 
00248 // <motivation>
00249 // This class assists in the definition of a Quantum Table Column.
00250 // </motivation>
00251 
00252 // <thrown>
00253 //    <li>AipsError during construction if the column doesn't exist.
00254 //    <li>AipsError during construction if the unit's column doesn't
00255 //        exist (when variable units).
00256 //    <li>AipsError during construction if the type of the variable unit's
00257 //        column is not String.
00258 //    <li>AipsError during a reconstruct if the column doesn't have a Unit.
00259 // </thrown>
00260 
00261 //# <todo asof="$DATE:$">
00262 //# A List of bugs, limitations, extensions or planned refinements.
00263 //# </todo>
00264 
00265 class TableQuantumDesc
00266 {
00267 public:
00268   // Constructs a Quantum column descriptor with null units (Unit == "").
00269   // The column should have already been added to the TableDesc.
00270   // An exception is thrown if the column doesn't exist.
00271   TableQuantumDesc (const TableDesc& td, const String& column);
00272 
00273   // Constructs a Quantum column descriptor with the specified Quantum unit.
00274   // The column should have already been added to the TableDesc.
00275   // An exception is thrown if the column doesn't exist.
00276   TableQuantumDesc (const TableDesc& td, const String& column, const Unit&);
00277 
00278   // Constructs a Quantum column descriptor with the specified Quantum units.
00279   // The column should have already been added to the TableDesc.
00280   // An exception is thrown if the column doesn't exist.
00281   // <group>
00282   TableQuantumDesc (const TableDesc& td, const String& column,
00283                     const Vector<String>& unitNames);
00284   TableQuantumDesc (const TableDesc& td, const String& column,
00285                     const Vector<Unit>&);
00286   // </group>
00287 
00288   // Constructs a Quantum column descriptor with variable units stored in
00289   // unitCol.  Both the quantum and unit column should exist in the
00290   // TableDesc.
00291   //# Note that the Char* constructor is needed, otherwise the compiler
00292   //# cannot choose between String and Unit.
00293   //<group>
00294   TableQuantumDesc (const TableDesc& td, const String& column,
00295                     const String& unitCol);
00296   TableQuantumDesc (const TableDesc& td, const String& column,
00297                     const Char* unitCol);
00298   //</group>
00299 
00300   // Copy constructor (copy semantics).
00301   TableQuantumDesc (const TableQuantumDesc& that);
00302 
00303   ~TableQuantumDesc();
00304 
00305   // Reconstructs a previously constructed TableQuantumDesc.
00306   static TableQuantumDesc* reconstruct (const TableDesc& td,
00307                                         const String& column);
00308 
00309   // Assignment.
00310   TableQuantumDesc& operator= (const TableQuantumDesc& that);
00311 
00312   // Returns the Quantum column descriptor's units.  A empty vector is
00313   // returned if units have not been specified.  This could be because the null
00314   // unit constructor was used or because the units are variable.
00315   const Vector<String>& getUnits() const
00316     { return itsUnitsName; }
00317 
00318   // Returns True if descriptor set for variable units (one per row)
00319   Bool isUnitVariable() const
00320     { return (! itsUnitsColName.empty()); }
00321 
00322   // Returns the name of the quantum column.
00323   const String& columnName() const
00324     { return itsColName; }
00325 
00326   // Returns the name of the units column (an empty String is returned
00327   // if the units are not variable).
00328   const String& unitColumnName() const
00329     { return itsUnitsColName; }
00330 
00331   // Makes the TableQuantumDesc persistent (updates the Table Descriptor).
00332   // <group>
00333   void write (TableDesc&);
00334   void write (Table&);
00335   // </group>
00336 
00337   // Does this column contain table quanta?
00338   static Bool hasQuanta (const TableColumn& column);
00339 
00340 private:
00341   // Name of column which stores the Quantum's values.
00342   String itsColName;
00343   // The Quantum's unit as a string.
00344   Vector<String> itsUnitsName;
00345   // Name of units column if units are variable.
00346   String itsUnitsColName;
00347 
00348 
00349   // Write the actual keywords.
00350   void writeKeys (TableRecord& columnKeyset);
00351 
00352   // Throw an exception if the quantum column doesn't exist.
00353   void checkColumn (const TableDesc& td) const;
00354 
00355   // Throw an exception if the variable units column isn't a string column.
00356   void checkUnitsColumn (const TableDesc& td) const;
00357 };
00358 
00359 
00360 
00361 } //# NAMESPACE CASACORE - END
00362 
00363 #endif
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