This abstract base class defines the interface for classes which define the shape of a component. The most fundamental derived class is the point shape class but the Gaussian shape and disk shape classes are also available. These classes model the spatial distribution of emission from the sky.
Classes derived from the SpectralModel class are used to model the spectral characteristics and the Flux class is used to model the flux. The SkyComponent class incorporates these three characteristics (flux, shape & spectrum) and the ComponentList class handles groups of SkyComponent objects.
This base class parameterises shapes with two quantities.
The basic operation of classes using this interface is to model the flux as a function of direction on the sky. Classes derived from this one do not know what the flux of the component. Instead the sample and visibility functions return factors that are used to scale the flux and calculate the amount of flux at a specified point on the sky or on the (u,v) plane.
Any allowed direction reference frame can be used. However the reference frame must be adequately specified in order to allow conversions to other reference frames. For example if the reference frame code for a component is MDirection::AZEL then the reference frame must also contain the time and position, on the earth, that the specified azimuth and elevation to refer to. This way the sample functions can convert the direction to a value in the J2000 reference frame (if you specify the sample direction in the J2000 frame).
Because this is an abstract base class, an actual instance of this class cannot be constructed. However the interface it defines can be used inside a function. This is always recommended as it allows functions which have ComponentShapes as arguments to work for any derived class.
In this example the printShape function prints out the type of model it is working with and the reference direction of that model. This example is also available in the dPointShape.cc file.
void printShape(const ComponentShape& theShape) {
cout << "This is a " << ComponentType::name(theShape.type())
<< " shape " << endl
<< "with a reference direction of "
<< theShape.refDirection() << endl;
}
return the actual shape. The ident function returns it as a String.
set/get the reference direction
set/get the error in the reference direction. Values must be positive angular quantities otherwise an AipsError exception is thrown. The errors are usually interpreted as the 1-sigma bounds in latitude/longitude and implicitly assume a Gaussian distribution.
Calculate the proportion of the flux that is in a pixel of specified size centered in the specified direction. The returned value will always be between zero and one (inclusive).
Same as the previous function except that many directions can be sampled at once. The reference frame and pixel size must be the same for all the specified directions. A default implementation of this function is available that uses the single pixel sample function described above. However customised versions of this function will be more efficient as intermediate values only need to be computed once.
Return the Fourier transform of the component at the specified point in the spatial frequency domain. The point is specified by a 3-element vector (u,v,w) that has units of meters and the frequency of the observation, in Hertz. These two quantities can be used to derive the required spatial frequency (s = uvw*freq/c). The w component is not used in these functions. The scale factor returned by this function can be used to scale the flux at the origin of the Fourier plane in order to determine the visibility at the specified point.
The "origin" of the transform is the reference direction of the component. This means for symmetric components, where the reference direction is at the centre, that the Fourier transform will always be real.
Same as the previous function except that many (u,v,w) points can be sampled at once. The observation frequency is the same for all the specified points. The uvw Matrix must have first dimension of three and the second dimension must match the length of the scale vector. A default implementation of this function is available that uses the single point visibility function described above. However customised versions of this function may be more efficient as intermediate values only need to be computed once.
determine whether the shape is symmetric or not. If it is then all the scale factors returned by the visibility functions will be real numbers.
Return a pointer to a copy of the derived object upcast to a ComponentShape object. The class that uses this function is responsible for deleting the pointer. This is used to implement a virtual copy constructor.
return the number of parameters in this shape and set/get them. The error functions provide a way to set/get the error (nominally 1-sigma in an implicit Gaussian distribution) in the corresponding parameter.
These functions convert between a record and a ComponentShape. This way derived classes can interpret fields in the record in a class specific way. They return False if the record is malformed and append an error message to the supplied string giving the reason. These functions define how the shape is represented in glish. All records should have 'type' & 'direction' fields which contain respectively; a string indicating which shape is actually used, and a record representation of a direction measure. The interpretation of all other fields depends on the specific component shape used.
Convert the parameters of the shape to the specified units. The Record must contain the same fields that the to/from Record functions have (with the exception of the direction & type fields). These fields will contain strings (and not record representations of Quantums) that specify the new units for these parameters. The new units must have the same dimensions as the existing ones. If there is any problem parsing the record then an error message is appended to the supplied string and the function returns False.
Return the shape that the supplied record represents. The shape is determined by parsing a 'type' field in the supplied record. Returns ComponentType::UNKNOWN_SHAPE if the type field (which contains a string) could not be translated into a known shape. It then appends an appropriate error message to the errorMessage String.
Convert component shape to absolute pixels. The returned vector is the longitude and latitude location in absolute pixels.
Fill the shape direction from the vector (longitude and latitude in absolute pixels). The return value is always True.
Function which checks the internal data of this class for correct dimensionality and consistant values. Returns True if everything is fine otherwise returns False.
returns True if the quantum is not a non-negative angular quantity
Turns the specified field in the specified record into an Quantum with angular units