ssISAR Class Reference

This class provides the implementation of ISAR. More...

Public Member Functions
	ssISAR ()
	Default Constructor.
	~ssISAR ()
	Default Destructor.
void	setNoiseParameters (float power_law, float scale_coefficient, float sea_state_shift)
	This function sets the parameters that determine how sea state noise is added to the scene.
void	addShipInView (ssShipMotion *shipMotion, ssObject *shipObject)
	This class maintains a list of ship motion objects that are within view.
void	clearShipsInView ()
	This class maintains a list of ship motion objects that are within view.
int	getNumShipsInView ()
	Return the number of ships that this class has been told are in view for the current integration cycle.
bool	update (ssSensor *sensor)
	Update this ISAR sensor implementation.
double	getSimulationTime ()
	Get the currently simulation time, in seconds, based on the timer that is being used by this ISAR sensor.
void	getDisplayImageProperties (float &CPI_s, float &minIntensity, float &maxIntensity, float &minRange, float &maxRange, float &minRangeRate, float &maxRangeRate, int &numRangePixels, int &numRangeRatePixels)
	Get Display image (not ISAR image) final properties.
void	computeIsarImage (float *imageData, int imageWidth, int imageHeight, int components, float horzFOV, float vertFOV, ssSensor *sensor)
	At the end of an integration period, this method should be called to generate an ISAR image from the images that have been generated for this period.
void	setUseVectorISAR (bool flag)
bool	getUseVectorISAR ()

Private Member Functions
void	unscaleDoppler (float *imgData, int imgWidth, int imgHeight, int components, ssSensor *sensor)
void	findAxisExtents (float *imgData, int imgWidth, int imgHeight, int components, ISAR_LIMITS &limits, ssSensor *sensor)
void	constructImage (float *imgData, int imgWidth, int imgHeight, int components, bool area_weight, float minAbsRangeRate, ISAR_LIMITS limits)
	Creates an ISAR image using a radiance array as input.
void	computeNumSensorBins (ssSensor *sensor, double sample_time_start_sec, double sample_time_end_sec, int maxHorzBins, int maxVertBins, ISAR_LIMITS &limits)
	Approximates the horizontal, vertical bin counts using the arc/aperture determined due to a continuous ship rotation without changes direction.
VECTOR	computeMaxFlipTimeInterval (ssSensor *sensor, double maxDeltaTimeStep, double angularTolDeg=60)
	Calculates the maximum time interval for a continuous ship rotation without changes direction.
void	computeSensorLookAngles (double &x_rad, double &y_rad, double &z_rad, ssSensor *sensor, double sample_time_sec)
	Calculates the Ship Rotation to position ship for notional ISAR view.
double	computeApparentArc (ssSensor *sensor, double sample_time_start_sec, double sample_time_end_sec)
	Uses the contiguous sampling times returned by computeMaxFlipTimeInterval().
VECTOR	getCurrentPath (ssSensor *sensor)
VECTOR	computePathAngularVelocity (ssSensor *sensor, double sample_time_sec)
	Calculates the Ship Motion Rotation Matrix for relative ISAR position.
void	stretchRadianceArray (float *savedRadianceArray, int size, float fmin=0, float fmax=0)
	Modify the contents of the passed in array by applying gain and level.
void	outputTestFile (const char *fileName, const float *imageData, int imageWidth, int imageHeight, int counter)
	Opens the file that is specified by name and writes the contents of the passed in array of floating point values to that file.

Private Attributes
double	m_integrationPeriod
bool	m_isflipped
int	m_numHorizontalBins
int	m_numVerticalBins
float	m_CPI
ISAR_LIMITS	m_limits
int	m_numRangePixels
int	m_numRangeRatePixels
float	m_powerLaw
float	m_scaleCoefficient
float	m_seaStateShift
ssTimer *	m_integrationTimer
ssTimer *	m_simulationTimer
ssShipMotion *	m_activeShipMotion
ssObject *	m_activeShipObject
int	m_numShipsInView
bool	m_useVectorISAR

Detailed Description

This class provides the implementation of ISAR.

This class uses the rotational motion of the ship that is within view to determine the size of the synthetic aperture for this sensor during each integration period. The size of the synthetic aperture determines the resulting clarity of the final radar image.

Constructor & Destructor Documentation

ssISAR::ssISAR

(

)

Default Constructor.

ssISAR::~ssISAR

(

)

Default Destructor.

Member Function Documentation

void ssISAR::setNoiseParameters	(	float	power_law,
		float	scale_coefficient,
		float	sea_state_shift
	)

This function sets the parameters that determine how sea state noise is added to the scene.

These parameters and algorithms require updates for better fidelity. There are currently no physics here!

    scale_coefficient*(sea_state+sea_state_shift)^power_law

Parameters

[in]	power_law	- exponent of the equation used to model noise
[in]	scale_coefficient	- coefficient of the equation used to model noise
[in]	sea_state_shift	- additive term to sea state in the equation used to model noise

void ssISAR::addShipInView	(	ssShipMotion *	shipMotion,
		ssObject *	shipObject
	)

This class maintains a list of ship motion objects that are within view.

This method should be used in conjunction with clearShipsInView() to maintain an accurate list of which ships are currently within view. The motion of these ships are used to compute the resolution of the ISAR image.

Parameters

shipMotion

- The ship motion object that should be added to our list of active ships.

void ssISAR::clearShipsInView ( )

inline

This class maintains a list of ship motion objects that are within view.

This method remove all ships motion objects that this class is using and should be used in conjunction with addShipInView() to maintain an accurate list of which ships are currently within view.

int ssISAR::getNumShipsInView ( )

inline

Return the number of ships that this class has been told are in view for the current integration cycle.

bool ssISAR::update

(

ssSensor *

sensor

)

Update this ISAR sensor implementation.

If the return value is true, a new ISAR image should be created this frame, which means that computeIsarImage() should be called. If false is returned, computeIsarImage() should not be called this frame.

Parameters

sensor	- Sensor that is currently being used
windSpeed	- The speed of the wind in knots

Returns

True if a new ISAR image should be created this frame, false if it should not.

double ssISAR::getSimulationTime

(

)

Get the currently simulation time, in seconds, based on the timer that is being used by this ISAR sensor.

void ssISAR::getDisplayImageProperties	(	float &	CPI_s,
		float &	minIntensity,
		float &	maxIntensity,
		float &	minRange,
		float &	maxRange,
		float &	minRangeRate,
		float &	maxRangeRate,
		int &	numRangePixels,
		int &	numRangeRatePixels
	)

Get Display image (not ISAR image) final properties.

void ssISAR::computeIsarImage	(	float *	imageData,
		int	imageWidth,
		int	imageHeight,
		int	components,
		float	horzFOV,
		float	vertFOV,
		ssSensor *	sensor
	)

At the end of an integration period, this method should be called to generate an ISAR image from the images that have been generated for this period.

The location of the sensor relative to the ship (it is pitching and rolling) has been used to generate multiple images that make the synthetic aperture of the radar. This call brings those images together to form a single higher quality image.

Parameters

imageData	- The most recently rendered image of the ship
imageWidth	- Pixel width of the image that is being passed in
imageHeight	- Pixel height of the image that is being passed in
components	- number of color channels per pixel
horzFOV	- The current horizontal field-of-view of the camera
vertFOV	- The current vertical field-of-view of the camera
sensor	- Sensor that is currently being used

void ssISAR::setUseVectorISAR ( bool  flag )

inline

bool ssISAR::getUseVectorISAR ( )

inline

void ssISAR::unscaleDoppler ( float *  imgData, int  imgWidth, int  imgHeight, int  components, ssSensor *  sensor  )

private

void ssISAR::findAxisExtents ( float *  imgData, int  imgWidth, int  imgHeight, int  components, ISAR_LIMITS &  limits, ssSensor *  sensor  )

private

void ssISAR::constructImage ( float *  imgData, int  imgWidth, int  imgHeight, int  components, bool  area_weight, float  minAbsRangeRate, ISAR_LIMITS  limits  )

private

Creates an ISAR image using a radiance array as input.

This method my be one of the most important in the entire ISAR implementations. The rendered ship is passes in as a full resolution radiance array. The image is processed to represent the ISAR image by scaling it based on the number of passed in range and cross-range bins. The resulting ISAR image is then written back into the image array that was passed in.

Parameters

[in,out]	imgData	- radiance array in, ISAR image out
	imgWidth	- Pixel width of the image that is being passed in
	imgHeight	- Pixel height of the image that is being passed in
	components	- number of color channels per pixel
	area_weight	- if true, assumes intensity should be redistributed when binning such that intensity/unitarea is conserved.
	minAbsRangeRate	- min detectable target velocity [m/s]
	limits	- min/max limits found from scenegraph sampling for intensity, range, rangerate. /////////////////////////////////////////////////////////////////////////

void ssISAR::computeNumSensorBins ( ssSensor *  sensor, double  sample_time_start_sec, double  sample_time_end_sec, int  maxHorzBins, int  maxVertBins, ISAR_LIMITS &  limits  )

private

Approximates the horizontal, vertical bin counts using the arc/aperture determined due to a continuous ship rotation without changes direction.

This thethod uses ISARSensorApparentArc() and assumes ship coordinate origin are set at the metacentric height, the ship's length lies along the x-axis, and the z-axis is vertical

Parameters

sensor	- current sensor object
sample_time_start_sec	- calculation start time in seconds
sample_time_end_sec	- calculation end time in seconds
maxHorzBins	- maximum number of bins there can be in the horizontal direction
maxVertBins	- maximum number of bins there can be in the vertical direction
limits	- min/max limits found from scenegraph sampling for intensity, range, rangerate. /////////////////////////////////////////////////////////////////////////

VECTOR ssISAR::computeMaxFlipTimeInterval ( ssSensor *  sensor, double  maxDeltaTimeStep, double  angularTolDeg = 60  )

private

Calculates the maximum time interval for a continuous ship rotation without changes direction.

Assumes ship coordinate origin are set at the metacentric height, Ship length lies along the x-axis, z-axis is vertical

Parameters

sensor	- Current sensor object
maxDeltaTimeStep	- Largest acceptable time step (seconds) that can be taken to sample the rotational motion
angularTolDeg	- threshold of minimum change in angle [degree] of the ship tangential (rotation) velocity that denotes change in direction. The art of good enough. sigh...

Returns

maximum time interval (start and stop time in seconds) of continuous rotation in the sampling interval

void ssISAR::computeSensorLookAngles ( double &  x_rad, double &  y_rad, double &  z_rad, ssSensor *  sensor, double  sample_time_sec  )

private

Calculates the Ship Rotation to position ship for notional ISAR view.

Assumes ship coordinate origin are set at the metacentric height, Ship length lies along the x-axis, z-axis is vertical.

NOTE: y-rad needs to be checked as it is not currently used

Parameters

[out]	x_rad	- rotation angle [radians] with z-axis as rotor(heading)
[out]	y_rad	- rotation angle [radians] with y-axis as rotor HOWEVER this rotation is not currently needed/used
[out]	z_rad	- rotation angle [radians] with x-axis as rotor(roll)
	sensor	- current sensor object
	sample_time_sec	- elapsed time in seconds

double ssISAR::computeApparentArc ( ssSensor *  sensor, double  sample_time_start_sec, double  sample_time_end_sec  )

private

Uses the contiguous sampling times returned by computeMaxFlipTimeInterval().

Assumes ship coordinate origin are set at the metacentric height, Ship length lies along the x-axis, z-axis is vertical

Parameters

sensor	- current sensor object
sample_time_start_sec	- calculation start time in seconds
sample_time_end_sec	- calculation end time in seconds

Returns

angle width in radians of the arc

VECTOR ssISAR::getCurrentPath ( ssSensor *  sensor )

private

VECTOR ssISAR::computePathAngularVelocity ( ssSensor *  sensor, double  sample_time_sec  )

private

Calculates the Ship Motion Rotation Matrix for relative ISAR position.

Assumes ship coordinate origin are set at the metacentric height, Ship length lies along the x-axis, z-axis is vertical.

NOTE: Sensor look is not needed currently

Parameters

sensor	- current sensor object
sample_time_sec	- elapsed time in seconds

Returns

Path Angular Velocity Vector for notional position in homogeneous coordinates

void ssISAR::stretchRadianceArray ( float *  savedRadianceArray, int  size, float  fmin = 0, float  fmax = 0  )

private

Modify the contents of the passed in array by applying gain and level.

The manipulation will result in the minimum and maximum values stored in the array matching the passed in values for min and max. All array value in between these two value will be modified so that they maintain their relative spacing between these new min and max values. This manipulation will "stretch" the values stored in the array so that they range from the passed in min to the passed in max.

void ssISAR::outputTestFile ( const char *  fileName, const float *  imageData, int  imageWidth, int  imageHeight, int  counter  )

private

Opens the file that is specified by name and writes the contents of the passed in array of floating point values to that file.

Member Data Documentation

double ssISAR::m_integrationPeriod

private

bool ssISAR::m_isflipped

private

int ssISAR::m_numHorizontalBins

private

int ssISAR::m_numVerticalBins

private

float ssISAR::m_CPI

private

ISAR_LIMITS ssISAR::m_limits

private

int ssISAR::m_numRangePixels

private

int ssISAR::m_numRangeRatePixels

private

float ssISAR::m_powerLaw

private

float ssISAR::m_scaleCoefficient

private

float ssISAR::m_seaStateShift

private

ssTimer* ssISAR::m_integrationTimer

private

ssTimer* ssISAR::m_simulationTimer

private

ssShipMotion* ssISAR::m_activeShipMotion

private

ssObject* ssISAR::m_activeShipObject

private

int ssISAR::m_numShipsInView

private

bool ssISAR::m_useVectorISAR

private

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The documentation for this class was generated from the following file:

• ssISAR.h