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Lunar lander code clarity (#354)
This commit is contained in:
Cameron Cooke
GitHub
@@ -47,8 +47,11 @@ LEG_DOWN = 18
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LEG_W, LEG_H = 2, 8
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LEG_SPRING_TORQUE = 40
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SIDE_ENGINE_HEIGHT = 14.0
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SIDE_ENGINE_AWAY = 12.0
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SIDE_ENGINE_HEIGHT = 14
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SIDE_ENGINE_AWAY = 12
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MAIN_ENGINE_Y_LOCATION = (
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4 # The Y location of the main engine on the body of the Lander.
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)
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VIEWPORT_W = 600
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VIEWPORT_H = 400
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@@ -183,6 +186,34 @@ class LunarLander(gym.Env, EzPickle):
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renormalized to 200; harder initial random push.
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- v0: Initial version
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## Notes
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There are several unexpected bugs with the implementation of the environment.
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1. The position of the side thursters on the body of the lander changes, depending on the orientation of the lander.
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This in turn results in an orientation depentant torque being applied to the lander.
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2. The units of the state are not consistent. I.e.
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* The angular velocity is in units of 0.4 radians per second. In order to convert to radians per second, the value needs to be multiplied by a factor of 2.5.
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For the default values of VIEWPORT_W, VIEWPORT_H, SCALE, and FPS, the scale factors equal:
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'x': 10
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'y': 6.666
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'vx': 5
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'vy': 7.5
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'angle': 1
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'angular velocity': 2.5
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After the correction has been made, the units of the state are as follows:
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'x': (units)
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'y': (units)
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'vx': (units/second)
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'vy': (units/second)
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'angle': (radians)
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'angular velocity': (radians/second)
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<!-- ## References -->
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## Credits
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@@ -327,7 +358,7 @@ class LunarLander(gym.Env, EzPickle):
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W = VIEWPORT_W / SCALE
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H = VIEWPORT_H / SCALE
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# terrain
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# Create Terrain
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CHUNKS = 11
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height = self.np_random.uniform(0, H / 2, size=(CHUNKS + 1,))
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chunk_x = [W / (CHUNKS - 1) * i for i in range(CHUNKS)]
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@@ -357,9 +388,11 @@ class LunarLander(gym.Env, EzPickle):
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self.moon.color1 = (0.0, 0.0, 0.0)
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self.moon.color2 = (0.0, 0.0, 0.0)
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# Create Lander body
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initial_y = VIEWPORT_H / SCALE
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initial_x = VIEWPORT_W / SCALE / 2
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self.lander: Box2D.b2Body = self.world.CreateDynamicBody(
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position=(VIEWPORT_W / SCALE / 2, initial_y),
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position=(initial_x, initial_y),
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angle=0.0,
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fixtures=fixtureDef(
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shape=polygonShape(
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@@ -374,6 +407,8 @@ class LunarLander(gym.Env, EzPickle):
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)
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self.lander.color1 = (128, 102, 230)
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self.lander.color2 = (77, 77, 128)
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# Apply the initial random impulse to the lander
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self.lander.ApplyForceToCenter(
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(
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self.np_random.uniform(-INITIAL_RANDOM, INITIAL_RANDOM),
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@@ -382,10 +417,11 @@ class LunarLander(gym.Env, EzPickle):
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True,
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)
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# Create Lander Legs
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self.legs = []
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for i in [-1, +1]:
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leg = self.world.CreateDynamicBody(
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position=(VIEWPORT_W / SCALE / 2 - i * LEG_AWAY / SCALE, initial_y),
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position=(initial_x - i * LEG_AWAY / SCALE, initial_y),
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angle=(i * 0.05),
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fixtures=fixtureDef(
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shape=polygonShape(box=(LEG_W / SCALE, LEG_H / SCALE)),
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@@ -450,7 +486,7 @@ class LunarLander(gym.Env, EzPickle):
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def step(self, action):
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assert self.lander is not None
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# Update wind
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# Update wind and apply to the lander
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assert self.lander is not None, "You forgot to call reset()"
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if self.enable_wind and not (
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self.legs[0].ground_contact or self.legs[1].ground_contact
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@@ -489,9 +525,15 @@ class LunarLander(gym.Env, EzPickle):
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action
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), f"{action!r} ({type(action)}) invalid "
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# Engines
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# Apply Engine Impulses
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# Tip is a the (X and Y) components of the rotation of the lander.
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tip = (math.sin(self.lander.angle), math.cos(self.lander.angle))
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# Side is the (-Y and X) components of the rotation of the lander.
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side = (-tip[1], tip[0])
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# Generate two random numbers between -1/SCALE and 1/SCALE.
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dispersion = [self.np_random.uniform(-1.0, +1.0) / SCALE for _ in range(2)]
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m_power = 0.0
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@@ -504,12 +546,21 @@ class LunarLander(gym.Env, EzPickle):
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assert m_power >= 0.5 and m_power <= 1.0
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else:
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m_power = 1.0
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# 4 is move a bit downwards, +-2 for randomness
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ox = tip[0] * (4 / SCALE + 2 * dispersion[0]) + side[0] * dispersion[1]
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oy = -tip[1] * (4 / SCALE + 2 * dispersion[0]) - side[1] * dispersion[1]
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# The components of the impulse to be applied by the main engine.
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ox = (
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tip[0] * (MAIN_ENGINE_Y_LOCATION / SCALE + 2 * dispersion[0])
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+ side[0] * dispersion[1]
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)
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oy = (
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-tip[1] * (MAIN_ENGINE_Y_LOCATION / SCALE + 2 * dispersion[0])
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- side[1] * dispersion[1]
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)
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impulse_pos = (self.lander.position[0] + ox, self.lander.position[1] + oy)
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if self.render_mode is not None:
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# particles are just a decoration, so don't add them when not rendering
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# particles are just a decoration, with no impact on the physics, so don't add them when not rendering
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p = self._create_particle(
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3.5, # 3.5 is here to make particle speed adequate
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impulse_pos[0],
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@@ -534,30 +585,43 @@ class LunarLander(gym.Env, EzPickle):
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if (self.continuous and np.abs(action[1]) > 0.5) or (
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not self.continuous and action in [1, 3]
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):
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# Orientation engines
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# Orientation/Side engines
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if self.continuous:
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direction = np.sign(action[1])
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s_power = np.clip(np.abs(action[1]), 0.5, 1.0)
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assert s_power >= 0.5 and s_power <= 1.0
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else:
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# action = 1 is left, action = 3 is right
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direction = action - 2
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s_power = 1.0
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# The components of the impulse to be applied by the side engines.
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ox = tip[0] * dispersion[0] + side[0] * (
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3 * dispersion[1] + direction * SIDE_ENGINE_AWAY / SCALE
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)
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oy = -tip[1] * dispersion[0] - side[1] * (
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3 * dispersion[1] + direction * SIDE_ENGINE_AWAY / SCALE
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)
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# The constant 17 is a constant, that is presumably meant to be SIDE_ENGINE_HEIGHT.
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# However, SIDE_ENGINE_HEIGHT is defined as 14
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# This casuses the position of the thurst on the body of the lander to change, depending on the orientation of the lander.
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# This in turn results in an orientation depentant torque being applied to the lander.
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impulse_pos = (
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self.lander.position[0] + ox - tip[0] * 17 / SCALE,
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self.lander.position[1] + oy + tip[1] * SIDE_ENGINE_HEIGHT / SCALE,
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)
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p = self._create_particle(0.7, impulse_pos[0], impulse_pos[1], s_power)
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p.ApplyLinearImpulse(
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(ox * SIDE_ENGINE_POWER * s_power, oy * SIDE_ENGINE_POWER * s_power),
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impulse_pos,
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True,
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)
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if self.render_mode is not None:
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# particles are just a decoration, with no impact on the physics, so don't add them when not rendering
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p = self._create_particle(0.7, impulse_pos[0], impulse_pos[1], s_power)
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p.ApplyLinearImpulse(
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(
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ox * SIDE_ENGINE_POWER * s_power,
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oy * SIDE_ENGINE_POWER * s_power,
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),
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impulse_pos,
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True,
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)
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self.lander.ApplyLinearImpulse(
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(-ox * SIDE_ENGINE_POWER * s_power, -oy * SIDE_ENGINE_POWER * s_power),
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impulse_pos,
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@@ -568,6 +632,7 @@ class LunarLander(gym.Env, EzPickle):
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pos = self.lander.position
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vel = self.lander.linearVelocity
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state = [
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(pos.x - VIEWPORT_W / SCALE / 2) / (VIEWPORT_W / SCALE / 2),
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(pos.y - (self.helipad_y + LEG_DOWN / SCALE)) / (VIEWPORT_H / SCALE / 2),
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