skyview.geometry

Class Projecter

java.lang.Object

skyview.geometry.Transformer

skyview.geometry.Projecter

All Implemented Interfaces:

java.io.Serializable, Component

Direct Known Subclasses:

Ait, Arc, Cah, Car, Csc, Hpx, Mer, Mol, Sfl, Sin, Stg, Tan, Tea, Toa, Tot, Zea, Zpn

public abstract class Projecter
extends Transformer

This class is the parent class for Transformers that project a point from the celestial sphere to a projection plane. Implementation within SkyView of a projection requires: - Creation of the Xxx projection class where Xxx is the three letter WCS name for the class (e.g., Tan, Sin, Mer, ...) The projecter class file normally includes * The mathematical transformation between the sphere and plane. * The associated deprojecter as an embedded class. * Where feasible the methods that implement straddling lines in the projection and shadow points. An associated straddler class may be defined. * Information as to whether the projection may be extended in the X and Y directions. - For fixed projections, an entry in the fixedPoints hash of the Projecter class. - For projections that are intended to be available as output projections in the Web interface * an entry in the basic query form to allow the selection of this projection for output * an update of the JavaScript classes that enable users to see the coordinates associated with an image point in the image output.

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
Projecter()

Method Summary

Modifier and Type	Method and Description
boolean	allValid() Are all points in the projection plane valid?
protected int	getInputDimension() What is the input dimensionality of a projecter?
protected int	getOutputDimension() What is the output dimensionality of a projecter?
double	getXTiling() Some projections can tile the projection plane with repeated copies.
double	getYTiling() The tiling period in Y
abstract Deprojecter	inverse() Get the inverse
double[]	shadowPoint(double x, double y) Return a shadowpoint for the input location.
boolean	straddle(double[][] pnts) Does this pixel go wrap around the standard region of the image? E.g., does it straddle the 180 deg in a Car or Ait projection?
boolean	straddleable() Is it possible for a pixel to straddle the valid region.
double[][][]	straddleComponents(double[][] pnts) If this is a straddling pixel, then return the straddle components
double[]	tissot(double x, double y) Return the Tissot ellipse parameters for the projection.
boolean	validPosition(double[] pos) Is this a valid position in the projection plane for this image.

Methods inherited from class skyview.geometry.Transformer

isInverse, transform, transform, transform

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface skyview.Component

getDescription, getName

Constructor Detail

Projecter

public Projecter()

Method Detail

inverse

public abstract Deprojecter inverse()

Get the inverse

Specified by:

inverse in class Transformer

getOutputDimension

protected int getOutputDimension()

What is the output dimensionality of a projecter?

Specified by:

getOutputDimension in class Transformer

getInputDimension

protected int getInputDimension()

What is the input dimensionality of a projecter?

Specified by:

getInputDimension in class Transformer

getXTiling

public double getXTiling()

Some projections can tile the projection plane with repeated copies. This method gives the vectors along which the tiles repeat. Note that for azimuthal like (e.g., Mercator) projections, the tiling may be possible in the longitudinal direction, but not in the latitudinal direction. Some projections (e.g., CAR) can tile in both directions (but note that the periodicity for tiling is 360 degrees in both directions in the CAR projection since the latitudes will run ... -90 -80 ...0 ... 80 90 80 ... 0 ... -80 -90 -80 ....

Returns:

The period in X in radians. A value of 0 means that there is not periodicity.

getYTiling

public double getYTiling()

The tiling period in Y

Returns:

The tiling period in radians. A value of 0 means that there is no period.

validPosition

public boolean validPosition(double[] pos)

Is this a valid position in the projection plane for this image. This default is appropriate for all projections where the projection plane is infinite.

allValid

public boolean allValid()

Are all points in the projection plane valid?

straddleable

public boolean straddleable()

Is it possible for a pixel to straddle the valid region.

straddle

public boolean straddle(double[][] pnts)

Does this pixel go wrap around the standard region of the image? E.g., does it straddle the 180 deg in a Car or Ait projection?

straddleComponents

public double[][][] straddleComponents(double[][] pnts)

If this is a straddling pixel, then return the straddle components

shadowPoint

public double[] shadowPoint(double x,
                            double y)

Return a shadowpoint for the input location. Shadowpoints are not defined for all projections.

tissot

public double[] tissot(double x,
                       double y)

Return the Tissot ellipse parameters for the projection. This gives the axes and position angle of an ellipse that reflects the distotortion at the given point. If there is no distortion or rotation, then the values (1,1,0) are returned. If the major axis is aligned with latitude, then the angle (the third parameter) will be 0, or pi/2 if greater aligned with longitude. If the projection is equal-area then the first two parameters are multiplicative inverses. This implementation is a place holder which should be overriden by specific projections. It returns a set of NaNs to indicate that the calculation has not been done.

Parameters:

x - The X-value at which the Tissot indicatrix is to be calculated.

y - The Y-value at which the Tissot indicatrix is to be calculated.

Returns:

A three element double vector [Semimajor, semiminor, position angle] with the axes size and positional angle of the ellipse.