SolarSystemSimulator/NOTES.txt at master · markus-ebke/SolarSystemSimulator · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
Property groups (in properties.py):
sssim_scn (type: SSSIMScene)
    - sim_time
    - time_exp
    - length_exp
    - planet_size_mult
    - draw_orbit

sssim_obj (type: SSSIMObject)
    - use sssim
    - object_type
    - show_info
    - center
    # not used for surfaces:
    - mass_mantissa
    - mass_exp

sssim_orbit (type: SSSIMOrbit)
    - eccentricity
    - distance_mantissa
    - distance_exp
    - inclination
    - asc_node
    - arg_periapsis
    - time_offset
    - use_user_period
    - use_frames
    - user_period_seconds
    - user_period_frames

sssim_rotation (type: SSSIMRotation)
    - use_rotation
    - use_frames
    - user_period_frames
    - user_period_seconds
    - axis_tilt
    - axis_direction
    - relative_to_orbit

sssim_calc (type: SSSIMCalculation)
    - use_driver
    - cyclic
    - frame_start
    - frame_end
    - frame_step
    (- motion_path <- not useful)

sssim_surface (type: SSSIMSurface)
    - calc_radius
    # used internally:
    (- object_proportions)
    (- original_scale)
    - radius_mantissa
    - radius_exp

TODO:
- 3D-Viewport panel in "Tools" or "SSSim" category?
- Add drivers and simulation time F-Curve automatically via bpy.app.handlers.load_post?
- Help text: activate for every panel with (?) in upper corner
- Add option for "advanced settings"?
- Switch order of "Ascending Node" and "Argument of Periapsis" (research the usual convention)
- See https://danielk.developer.irf.se/pyorb/ for more features:
	- Implement parabolic and hyperbolic trajectories (use EnumProperty for type "circular", "elliptical", "parabolic", "hyperbolic"?)
	- Add toggle (EnumProperty) for alternative input: specify periapsis (and eccentricity) instead of semi-major axis (and eccentricity), works better for e >= 1 orbits
	- Input cartesian coordinates, i.e. specify (x, y, z, vx, vy, vz, t0), but convert to kepler elements
- Increase resolution of orbit path curve? Use Bezier circle with more than 4 nodes?
- "Bake" the simulation for dynamically changing orbit (e.g. when keyframing orbit properties):
```
import bpy


scn = bpy.context.scene
obj = bpy.context.object

# Frame range to bake
frame_start = scn.frame_start - 1
frame_end = scn.frame_end + 1
frame_step = 10  # number of frames to skip forward

# Compute locations via driver and save them
stash = dict()  # mapping {frame: location vector}
f = frame_start
while f <= frame_end:
    scn.frame_set(f)
    stash[f] = obj.location.copy()
    f += frame_step

# Then remove the driver
obj.driver_remove("location")

# Now create the location keyframes
for f, loc in stash.items():
    obj.location = loc
    obj.keyframe_insert(data_path="location", frame=f)
```
Finally, in the Graph Editor set the fcurve extrapolation mode to linear (Channel > Extrapolation Mode > Linear Extrapolation) to get the correct animation at the start and end of the scene.

LINKS:
http://www-spof.gsfc.nasa.gov/stargaze/Smap.htm
http://www-spof.gsfc.nasa.gov/stargaze/Skeplaws.htm
http://en.wikipedia.org/wiki/Orbital_elements
https://orbital-mechanics.space/intro.html