import numpy as np


class PerspCamera(object):
    r"""Perspective camera in 35mm format.

    Attributes:
        f_mm (float): See ``f``.
        im_h (float): See ``im_res``.
        im_w (float): See ``im_res``.
        loc (numpy.ndarray)
        lookat (numpy.ndarray)
        up (numpy.ndarray)

    Note:
        - Sensor width of the 35mm format is actually 36mm.
        - This class assumes unit pixel aspect ratio (i.e., :math:`f_x = f_y`)
          and no skewing between the sensor plane and optical axis.
        - The active sensor size may be smaller than ``sensor_size``, depending