Source code for irfpy.cena.centralpixel

''' A CENA FoV module.

CENA FoV is indeed a finite area in the angular space.
However, for simple investigation, the center vectors for each channel
can be used as a representation.  This module provides an implementation.

Use :mod:`irfpy.cena.fov` module for advanced and generic use.
'''
import math
from irfpy.util.vector3d import Vector3d
from irfpy.cena import frame

class Fov:
    ''' Abstract class of CENA FoV.
    '''

class FovIss1Rev1(Fov):
    ''' An implementation of CENA FoV.

    CENA FoV with central direction approximation.
    Data based on the calibration report issue 1 revision1.
    '''
    def __init__(self):
        '''
        '''

    def getDirection(self, ch):
        ''' Get the viewing vector in SC frame corresponding to the looking direction.

        Central azimuth direction, phi_c[n], is formulated as
        phi_c[n] = -19.06*n + 57.19         ...   Eq 3.2.
        FWHM is 45 degrees, but in this implementation, it is ignored.

        The elevation theta_c[n] is -6.05 degs in Eq. 3.4.
        FWHM is 6.44 degs while is ignored.
        

        >>> fov = FovIss1Rev1()

        The returned value is an instance of Vector3d.
        >>> v = fov.getDirection(0)
        >>> # print v.x, v.y, v.z

        If you specify the unexisting ch (other than 0 to 6),
        IndexError will be raised.

        >>> try:
        ...    fov.getDirection(-1)
        ...    print("Why didn't exception raised?")
        ... except IndexError as e:
        ...    print("Correct exception is raised.")
        ... except:
        ...    print("Unknonw exception raised.")
        Correct exception is raised.
        '''
        if ch<0 or ch>6:
            raise IndexError("CENA channels should be 0..6 (%s given)" % str(ch))

        theta = -6.05
        phi = (-19.06 * ch + 57.19)

        v_cena = self._angle2vec(theta, phi)
        v_sc = frame.cena2sc(v_cena)

        return v_sc

    @classmethod
    def _angle2vec(self, theta, phi):
        ''' Calculate the vector corresponding to theta and phi.

        According to the calibration report, theta is the angle from XY plane
        and -Z direction is +theta.
        phi is an azimuthal angle, and the origin is +Y and +X direction
        is +phi.

        theta and phi is in degrees.

        >>> v = FovIss1Rev1._angle2vec(0, 0)
        >>> v = FovIss1Rev1._angle2vec(90, 0)
        '''

        t = theta * math.pi / 180.
        p = phi * math.pi / 180.

        z = math.sin(-t)
        y = math.cos(-t) * math.cos(p)
        x = math.cos(-t) * math.sin(p)

        return Vector3d(x, y, z)
        


def defaultDirsSc():
    ''' Return a default direction of the CENA Fov in SC frame.

    Default direction of the CENA FOV is returned.
    The default uses FovIss1Rev1 class.
    The returned has 7 elements and each element is an
    instance of Vector3d object.

    >>> dir = defaultDirsSc()
    >>> print(len(dir))
    7
    >>> # print dir[3].x, dir[3].y, dir[3].z
    '''

    fov = FovIss1Rev1()
    vecs = []
    for i in range(7):
        vecs.append(fov.getDirection(i))

    return vecs