Abstract base class to steer lattice iterators. More...

#include <LatticeNavigator.h>

Inheritance diagram for casa::LatticeNavigator:

Public Member Functions
	LatticeNavigator ()
	Default constructor.
	LatticeNavigator (const LatticeNavigator &)
	Copy constructor.
LatticeNavigator &	operator= (const LatticeNavigator &)
	Assignment.
virtual	~LatticeNavigator ()
	A virtual destructor.
virtual Bool	operator++ (int)=0
	Increment operator - increment the cursor to the next position.
Bool	operator++ ()
virtual Bool	operator-- (int)=0
	Decrement operator - decrement the cursor to the previous position.
Bool	operator-- ()
virtual void	reset ()=0
	Function to reset the cursor to the beginning of the Lattice and reset the number of steps taken to zero.
virtual Bool	atStart () const =0
	Function which returns "True" if the cursor is at the beginning of the Lattice, otherwise, returns "False".
virtual Bool	atEnd () const =0
	Function which returns "True" if an attempt has been made to increment the cursor beyond the end of the Lattice.
virtual uInt	nsteps () const =0
	Function to return the number of steps (increments or decrements) taken since construction (or since last reset).
virtual IPosition	position () const =0
	Functions which return the current position of the beginning of the cursor.
virtual IPosition	relativePosition () const
virtual IPosition	endPosition () const =0
	Functions which return the current position of the end of the cursor.
virtual IPosition	relativeEndPosition () const
virtual IPosition	latticeShape () const =0
	Functions which return the shape of the Lattice being iterated through.
virtual IPosition	subLatticeShape () const
virtual IPosition	cursorShape () const =0
	Function which returns the current shape of the cursor which is iterating through the Lattice.
virtual IPosition	cursorAxes () const =0
	Function which returns the axes of the cursor.
virtual Bool	hangOver () const =0
	Function which returns "True" if the increment/decrement operators have moved the cursor position such that part of the cursor is hanging over the edge of the Lattice.
virtual IPosition	hangOverBlc () const
	Functions which return the "bottom left corner" and the "top right corner" of the cursor that does not hangover.
virtual IPosition	hangOverTrc () const
virtual void	subSection (const IPosition &blc, const IPosition &trc)
	Function to specify a "section" of the Lattice to Navigate over.
virtual void	subSection (const IPosition &blc, const IPosition &trc, const IPosition &inc)
virtual IPosition	blc () const
	Return the bottom left hand corner (blc), top right corner (trc) or step size (increment) used by the current sub-Lattice.
virtual IPosition	trc () const
virtual IPosition	increment () const
virtual const IPosition &	axisPath () const =0
	Return the axis path.
virtual uInt	calcCacheSize (const IPosition &cubeShape, const IPosition &tileShape, uInt maxCacheSize, uInt bucketSize) const =0
	Calculate the cache size (in tiles) for this type of access to a lattice in the given row of the tiled hypercube.
virtual LatticeNavigator *	clone () const =0
	Function which returns a pointer to dynamic memory of an exact copy of this LatticeNavigator.
virtual Bool	ok () const
	Function which checks the internals of the class for consistency.

Detailed Description

Abstract base class to steer lattice iterators.

Intended use:

Internal

Review Status

Reviewed By:: Peter Barnes
Date Reviewed:: 1999/10/30
Test programs:: tLatticeStepper

Prerequisite

Etymology

Lattice iteration can proceed with a number of different strategies - all of which answer the question: where do I go from here? You could travel through by making calculations on the lattice subscripts, viewing ascending planes in an image cube, for example, or you could travel through by making calculations on the data, viewing small subimage planes in order of descending brightness over the whole cube. Concrete classes derived from this base class implement different navigation strategies - but they are all "navigators".

Synopsis

This abstract base class defines the interface for objects which generate positions for LatticeIterators. This position is not just a single point in the Lattice but a region or "cursor" that is moved through the Lattice. The LatticeIterator classes actually retrieve the data in the cursor from the Lattice. The class decribed here (and those derived from it) are responsible for moving the cursor to the next position and determining its shape.

There may eventually be a large collection of tools for traversing Lattices. At this writing (December 1999) there are three concrete classes derived from LatticeNavigator: LatticeStepper , TiledLineStepper , and TileStepper .

The LatticeStepper class moves through a Lattice in fixed steps defined by the user specified cursor, incrementing to the next portion of the Lattice with each step, and wrapping around axes as needed. Other position generators might follow the brightest pixel, traverse a number of predefined subregions, or change size automatically when near the edges.

The TiledLineStepper class moves a Vector cursor through a Lattice, until all the lines in the set of tiles along the specified axis have been exhausted. It then moves to the next set of tiles. This is a memory-efficient way to move a Vector cursor through a Lattice.

The most important member functions of this class are those which move the cursor to the next position. These are the operator++ and operator-- member functions, (in postfix and prefix forms).

The cursor shape need not be constant as it moves through the Lattice, but may change depending on its current position. For the LatticeStepper and TiledLineStepper classes , however, the cursor shape is constant as it steps through the Lattice.

It is not possible to randomly move the cursor to an arbitrary place in the Lattice, although the cursor can be moved to the starting position at any time using the reset member function.

The position of the cursor can be queried at any time using the position member function. This gives the position of the bottom left hand corner of the cursor. The position of the top right hand corner of the cursor is obtained using the endPosition member function, and the current cursor shape is obtained using the cursorShape member function. Note that the endPosition does not take an overhang into account.

It is possible that for some positions of the cursor, part of it will "hang over" the edge of the Lattice. When this occurs the hangOver member function will return True. This will occur with a LatticeStepper if the Lattice shape is not a multiple of the cursor shape. Hangover cannot occur with the TiledLineStepper as the length of the Vector cursor is defined by the Lattice Shape.

It may be possible (depending on the concrete LatticeNavigator actually used) to specify that only a region of the Lattice (defined by a top right hand corner, bottom left hand corner, and step increment) be traversed by the LatticeNavigator. This is done using the subSection member function. At any time the region can be redefined by calling the subSection function again. This replaces the previously defined region with the new one.

Using the subSection function always sets the cursor position to the origin of the currently defined sub-lattice. This is a backdoor way to move the cursor to random locations in the Lattice.

It is an error to define a sub-lattice that is bigger than the current Lattice. If using a LatticeStepper it may also be necessary to resize the cursor (using the setCursorShape member function) prior to calling the subSection function as the cursor cannot be bigger than the sub-Lattice on any axis.

The arguments (trc, blc and inc) to the subSection function are always relative to the main Lattice. This is also true of the position and endPosition functions. To get the position of the cursor relative to the currently defined sub-Lattice use the relativePosition and relativeEndPosition member functions.

Many of the LatticeIterator member functions are directly forwarded to virtual functions of this class, and classes derived from it. For instance, LatticeIterator<T>::operator++() calls LatticeIterInterface->operator++() which calls LatticeNavigator->operator++() which might resolve to LatticeStepper->operator++(). Other functions like this are documented in the LatticeIterator class.

Example

See the examples in the LatticeStepper class, the TiledLineStepper class, and the TileStepper class.

Motivation

Iterator classes are quite common in C++. What's novel about the design which includes this class is the separation of iterator mechanisms from traversal strategy. The iterator provides a lot of functionality: it provides a cursor, damage notification and tracking, and reading and writing to the underlying data structure. Traversal strategies can and should be isolated from these things. Because every LatticeIterator uses a Navigator, it gets the benefits of a derived concrete navigator without getting involved in its mechanism.

To Do

Think about how to implement Navigators which can traverse arbitrary shaped regions.

Definition at line 182 of file LatticeNavigator.h.

Constructor & Destructor Documentation

casa::LatticeNavigator::LatticeNavigator ( ) [inline]

Default constructor.

Definition at line 185 of file LatticeNavigator.h.

casa::LatticeNavigator::LatticeNavigator ( const LatticeNavigator & ) [inline]

Copy constructor.

Definition at line 189 of file LatticeNavigator.h.

virtual casa::LatticeNavigator::~LatticeNavigator ( ) [virtual]

A virtual destructor.

A virtual is needed to ensure that derived classes accessed through pointers to a LatticeNavigator will scope their destructor to the derived class destructor.

Member Function Documentation

virtual Bool casa::LatticeNavigator::atEnd ( ) const [pure virtual]

Function which returns "True" if an attempt has been made to increment the cursor beyond the end of the Lattice.

Implemented in casa::LatticeStepper, casa::TiledLineStepper, and casa::TileStepper.

virtual Bool casa::LatticeNavigator::atStart ( ) const [pure virtual]

Function which returns "True" if the cursor is at the beginning of the Lattice, otherwise, returns "False".

Implemented in casa::LatticeStepper, casa::TiledLineStepper, and casa::TileStepper.

virtual const IPosition& casa::LatticeNavigator::axisPath ( ) const [pure virtual]

Return the axis path.

See LatticeStepper for a description and examples.

Implemented in casa::LatticeStepper, casa::TiledLineStepper, and casa::TileStepper.

virtual IPosition casa::LatticeNavigator::blc ( ) const [virtual]

Return the bottom left hand corner (blc), top right corner (trc) or step size (increment) used by the current sub-Lattice.

In the default implementation of this class sub-sectioning is not supported and these functions will always return blc=0, trc=latticeShape-1, increment=1, ie. the entire Lattice.

Reimplemented in casa::LatticeStepper, casa::TiledLineStepper, and casa::TileStepper.

virtual uInt casa::LatticeNavigator::calcCacheSize	(	const IPosition &	cubeShape,
		const IPosition &	tileShape,
		uInt	maxCacheSize,
		uInt	bucketSize
	)		const `[pure virtual]`

Calculate the cache size (in tiles) for this type of access to a lattice in the given row of the tiled hypercube.

A zero bucket size indicates that the data are not tiled, but in memory. Then a cache size of 0 is returned.

Implemented in casa::LatticeStepper, casa::TiledLineStepper, and casa::TileStepper.

virtual LatticeNavigator* casa::LatticeNavigator::clone ( ) const [pure virtual]

Function which returns a pointer to dynamic memory of an exact copy of this LatticeNavigator.

It is the responsibility of the caller to release this memory.

Implemented in casa::LatticeStepper, casa::TiledLineStepper, and casa::TileStepper.

virtual IPosition casa::LatticeNavigator::cursorAxes ( ) const [pure virtual]

Function which returns the axes of the cursor.

These are the axes which should not be removed by the iterator functions vectorCursor(), etc..

Implemented in casa::LatticeStepper, casa::TiledLineStepper, and casa::TileStepper.

virtual IPosition casa::LatticeNavigator::cursorShape ( ) const [pure virtual]

Function which returns the current shape of the cursor which is iterating through the Lattice.

The returned IPosition will have the same number of axes as the underlying Lattice.

Implemented in casa::LatticeStepper, casa::TiledLineStepper, and casa::TileStepper.

virtual IPosition casa::LatticeNavigator::endPosition ( ) const [pure virtual]

Functions which return the current position of the end of the cursor.

The endPosition function is relative to the origin in the main Lattice and the relativeEndPosition function is relative to the origin and increment used in the sub-Lattice (defined using the subSection function). The returned IPosition will have the same number of axes as the underlying Lattice.
Caution: It returns the end position in the lattice and does not take overhang into account;

The default implementation of the relativeEndPosition function returns (endPosition() - blc()) / increment().

Implemented in casa::LatticeStepper, casa::TiledLineStepper, and casa::TileStepper.

virtual Bool casa::LatticeNavigator::hangOver ( ) const [pure virtual]

Function which returns "True" if the increment/decrement operators have moved the cursor position such that part of the cursor is hanging over the edge of the Lattice.

This function may always return a value of "False" for some iteration methods that do not move the cursor past the Lattice boundaries.

Implemented in casa::LatticeStepper, casa::TiledLineStepper, and casa::TileStepper.

virtual IPosition casa::LatticeNavigator::hangOverBlc ( ) const [virtual]

Functions which return the "bottom left corner" and the "top right corner" of the cursor that does not hangover.

Use these functions to extract the valid part of the cursor when the hangover member function is true. If there is no hangover then hangOverBLC returns an IPosition of zero and hangOverTRC() returns the cursorShape - 1;

virtual IPosition casa::LatticeNavigator::hangOverTrc ( ) const [virtual]

virtual IPosition casa::LatticeNavigator::increment ( ) const [virtual]

Reimplemented in casa::LatticeStepper, casa::TiledLineStepper, and casa::TileStepper.

virtual IPosition casa::LatticeNavigator::latticeShape ( ) const [pure virtual]

Functions which return the shape of the Lattice being iterated through.

latticeShape always returns the shape of the main Lattice while subLatticeShape returns the shape of any sub-Lattice defined using the subSection function. In the default implementation of this class it is not possible to use the subsection function (it throws an exception) so the default implementation of the subLatticeShape function calls the latticeShape function. The returned IPosition will always have the same number of axes as the underlying Lattice.

Implemented in casa::LatticeStepper, casa::TiledLineStepper, and casa::TileStepper.

virtual uInt casa::LatticeNavigator::nsteps ( ) const [pure virtual]

Function to return the number of steps (increments or decrements) taken since construction (or since last reset).

This is a running count of all cursor movement since doing N increments followed by N decrements does not necessarily put the cursor back at the origin of the Lattice.

Implemented in casa::LatticeStepper, casa::TiledLineStepper, and casa::TileStepper.

virtual Bool casa::LatticeNavigator::ok ( ) const [virtual]

Function which checks the internals of the class for consistency.

Returns True if everything is fine otherwise returns False. The default implementation always returns True.

Reimplemented in casa::LatticeStepper, casa::TiledLineStepper, and casa::TileStepper.

virtual Bool casa::LatticeNavigator::operator++ ( int ) [pure virtual]

Increment operator - increment the cursor to the next position.

The implementation of the prefix operator calls the postfix one.

Implemented in casa::LatticeStepper, casa::TiledLineStepper, and casa::TileStepper.

Bool casa::LatticeNavigator::operator++ ( ) [inline]

Definition at line 354 of file LatticeNavigator.h.

virtual Bool casa::LatticeNavigator::operator-- ( int ) [pure virtual]

Decrement operator - decrement the cursor to the previous position.

The implementation of the prefix operator calls the postfix one.

Implemented in casa::LatticeStepper, casa::TiledLineStepper, and casa::TileStepper.

Bool casa::LatticeNavigator::operator-- ( ) [inline]

Definition at line 358 of file LatticeNavigator.h.

LatticeNavigator& casa::LatticeNavigator::operator= ( const LatticeNavigator & ) [inline]

Assignment.

Definition at line 193 of file LatticeNavigator.h.

virtual IPosition casa::LatticeNavigator::position ( ) const [pure virtual]

Functions which return the current position of the beginning of the cursor.

The position function is relative to the origin in the main Lattice and the relativePosition function is relative to the origin and increment used in the sub-Lattice (defined using the subSection function). The returned IPosition will have the same number of axes as the underlying Lattice.
The default implementation of the relativePosition function returns (position() - blc()) / increment().

Implemented in casa::LatticeStepper, casa::TiledLineStepper, and casa::TileStepper.

virtual IPosition casa::LatticeNavigator::relativeEndPosition ( ) const [virtual]

Reimplemented in casa::LatticeStepper.

virtual IPosition casa::LatticeNavigator::relativePosition ( ) const [virtual]

Reimplemented in casa::LatticeStepper.

virtual void casa::LatticeNavigator::reset ( ) [pure virtual]

Function to reset the cursor to the beginning of the Lattice and reset the number of steps taken to zero.

Implemented in casa::LatticeStepper, casa::TiledLineStepper, and casa::TileStepper.

virtual IPosition casa::LatticeNavigator::subLatticeShape ( ) const [virtual]

Reimplemented in casa::LatticeStepper, casa::TiledLineStepper, and casa::TileStepper.

virtual void casa::LatticeNavigator::subSection	(	const IPosition &	blc,
		const IPosition &	trc
	)		`[virtual]`

Function to specify a "section" of the Lattice to Navigate over.

A section is defined in terms of the Bottom Left Corner (blc), Top Right Corner (trc), and step size (inc), on ALL of its axes, including degenerate axes. The step size defaults to one if not specified. In the default implementation of this class subsectioning is not supported and using the subsection function will throw an exception (AipsError).

Reimplemented in casa::LatticeStepper, casa::TiledLineStepper, and casa::TileStepper.