Instrument Kernels

Instrument Kernels allow you to define sensors, cameras, and antennas attached to a spacecraft.

The Instrument Object

An Instrument defines the sensor's geometry relative to the spacecraft bus.

Mounting

The mounting is defined by a rigid transformation from the Spacecraft Body Frame to the Instrument Frame. - q_to_i: A quaternion (rotation) describing the orientation. - offset_i: A translation vector (lever arm) from the spacecraft center of mass to the sensor origin.

Field of View (FOV)

The FOV defines the sensitive volume of the instrument. - Conical: Circular FOV (e.g., dish antennas, LIDARs). Defined by a half_angle_deg. - Rectangular: Box FOV (e.g., camera sensors). Defined by x_half_angle_deg (Width) and y_half_angle_deg (Height). Assumes the boresight is +Z.

Functionality

FOV Margin

ANISE can compute the FOV Margin, which is the angle between the target and the nearest FOV boundary. - Positive: Target is inside. - Negative: Target is outside. - Zero: Target is exactly on the edge.

This property is continuous, making it suitable for the Analysis Engine's event finder. You can solve for margin = 0 to find exact entry/exit times.

Footprints

The footprint method projects the FOV boundary onto a target planetary body (Ellipsoid). - Raycasts the FOV edges. - Intersects with the target shape. - Returns a list of points (lat/lon/alt) forming the polygon of the footprint on the surface.

This accounts for the full chain: Inertial -> Spacecraft Body -> Instrument -> Ray -> Target Inertial -> Target Fixed.