Some refactor and tried to figure out the angles right

objects/generic.py

@@ -0,0 +1,25 @@
+import numpy as np
+
+class MovingEntity:
+    """Embedded entity in the world with a position."""
+
+    def __init__(self, world):
+        self.world = world
+        self.pos = np.array((0.0, 0.0, 0.0))  # (x, y, z) in local untilted coordinates
+
+    def get_pos_rotated(self):
+        """Return position rotated by world's tilt around y-axis."""
+        return self.world.rotate_point_y(self.pos)
+
+    def move(self, dx=0, dy=0, dz=0):
+        self.pos = (self.pos[0] + dx, self.pos[1] + dy, self.pos[2] + dz)
+
+class Target(MovingEntity):
+    def __init__(self, world, pos=(0.0, 0.0, 0.0)):
+        super().__init__(world)
+        self.pos = np.array(pos) # Store everything in numpy
+
+class Source(MovingEntity):
+    def __init__(self, world, pos=(10.0, 10.0, 10.0)):
+        super().__init__(world)
+        self.pos = np.array(pos)