Convex vs Engine Light Curves

Comparing light curves produced by the LightCurveEngine renderer and a simplified convex method

import matplotlib.pyplot as plt
import numpy as np
import seaborn as sns

import mirage as mr

Defining the object and BRDF

obj = mr.SpaceObject('cylinder.obj')
brdf = mr.Brdf('phong', cd=0.1, cs=0.9, n=30)

Defining the attitude profile

t_eval = np.linspace(0, 10, int(1e3) + 1)
q, _ = mr.propagate_attitude_torque_free(
    mr.hat(np.array([0.0, 0.0, 0.0, 1.0])),
    np.array([1.0, 1.0, 1.0]),
    np.diag([1, 2, 3]),
    t_eval,
)

dcm = mr.quat_to_dcm(q)
ovb = mr.stack_mat_mult_vec(dcm, np.array([[1, 0, 0]]))
svb = mr.stack_mat_mult_vec(dcm, np.array([[0, 1, 0]]))

We can now run the engine and compute a convex light curve:

mr.tic()
b_non_convex = mr.run_light_curve_engine(
    brdf,
    obj,
    svb,
    ovb,
    instances=25,
    instance_width_pix=540,
)
mr.toc()
b_convex = obj.convex_light_curve(brdf, svb, ovb)

print(b_non_convex, b_convex)

Elapsed time: 7.34e-01 seconds
[1.436186 1.431122 1.450145 ... 1.427974 1.347964 1.298291] [1.49668747 1.49674882 1.49692643 ... 1.46660954 1.40084044 1.33174767]

And plot the results

plt.figure()
sns.lineplot(x=t_eval, y=b_non_convex, errorbar=None)
sns.lineplot(x=t_eval, y=b_convex, errorbar=None)
plt.title(f'Light Curves for {obj.file_name}')
plt.xlabel('Time [s]')
plt.ylabel('Normalized brightness')
plt.legend(['LightCurveEngine', 'Convex'])
plt.grid()
# plt.show()

Plotting the error instead of the brightness values

plt.figure()
sns.lineplot(x=t_eval, y=b_non_convex - b_convex, errorbar=None)
plt.title(f'Light Curves Error for {obj.file_name}')
plt.xlabel('Time [s]')
plt.ylabel('Normalized brightness error')
plt.grid()
plt.show()

This is nice and small, which we like to see. If we repeat this process for a non-convex object, the error quickly becomes clear

obj = mr.SpaceObject('tess.obj')
brdf = mr.Brdf('phong', cd=0.5, cs=0.5, n=5)

b_non_convex = mr.run_light_curve_engine(brdf, obj, svb, ovb, instances=1)
b_non_convex_rotating = mr.run_light_curve_engine(
    brdf, obj, svb, ovb, instances=1, rotate_panels=True
)
b_convex = obj.convex_light_curve(brdf, svb, ovb)


plt.figure()
sns.lineplot(x=t_eval, y=b_non_convex, errorbar=None)
sns.lineplot(x=t_eval, y=b_non_convex_rotating, errorbar=None)
sns.lineplot(x=t_eval, y=b_convex, errorbar=None)
plt.title(f'Light Curves for {obj.file_name}')
plt.xlabel('Time [s]')
plt.ylabel('Normalized brightness')
plt.legend(['LightCurveEngine', 'LightCurveEngine - rotating panels', 'Convex'])
plt.grid()
plt.show()