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Changes for page Ball Physics

Last modified by Soeren Domroes on 2025/01/30 12:18
From version 13.3
edited by stu122612
on 2023/07/06 14:48
Change comment: Updated the relative links.
To version 3.1
edited by stu104225
on 2020/03/03 18:55
Change comment: There is no comment for this version

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1 -PP18.Pinball Project - Winter Term 201920.Project Documentation.WebHome
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1 -XWiki.stu122612
1 +XWiki.stu104225
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1 -The **ball physics model**'s main objective is to provide a point in time to the controller, when the ball is predicted to be hittable, in order to not let the ball fall into the drain.
2 -The code for what is described in this section can be found in the files "physics.cpp" and "physics.h".
1 +\\
3 3  
3 +== Task ==
4 4  
5 +The ball physics model is meant to do things ...
5 5  
6 -{{toc/}}
7 +\\
7 7  
8 -== Ball trajectory ==
9 -
10 -----
11 -
12 -The trajectory of a ball can be modeled to be parabolic. From two point //p// and //p_old// with corresponding timestamps, the velocity //v// is computed.
13 -For a future point in time //t//, with //t=0 //being the timestamp of// p//, we can then approximately predict the corresponding ball position using the following formulas.
14 -
15 -[[image:attach:Bildschirmfoto von 2020-03-07 12-21-22.png]]
16 -
17 -The incline of the playfield causes a vertical acceleration, which is modeled via a gravitational pull with the factor //g = sin(6°) * 9.81 m/s²//.
18 -The value of 6° is the incline of the playfield  measured on the physical device.
19 -
20 -== Prediction ==
21 -
22 -----
23 -
24 -The controller calls the function //full_prediction// passing it two subsequent ball positions with timestamps. From these a ball trajectory is inferred as described above.
25 -Along the trajectory future times are stepwise tested for whether the corresponding predicted position is in the flipper range.
26 -Once a position inside the flipper range is found the search is continued both forwards and backwards in smaller steps in order to find a good enough estimate of the first and last possible time to hit the ball.
27 -If the trajectory does not intersect the flipper range within a certain prediction frame (see below "**Prediction parameters**") a value far enough into the future is returned, that will be overwritten by subsequent predictions.
28 -
29 -With the current configuration the controller uses the middle point in time between the first and last possible time in order to be most positive to hit the ball.
30 -The computed velocity is also passed to the controller and used is some more advanced  tactical decisions like catching balls.
31 -
32 32  == Configuration ==
33 33  
34 -----
11 +=== Points of interest ===
35 35  
36 -=== Prediction parameters ===
13 +\\
37 37  
38 -(% class="wrapped" %)
39 -|=(((
40 -Parameter
41 -)))|=(((
42 -Description
43 -)))|=(((
44 -Default value
45 -)))
46 -|(((
47 -PREDICTION_FRAME
48 -)))|(((
49 -window size for prediction - How far
15 +[[image:attach:physics_points.png]]
50 50  
51 -into the future are predictions calculated at most.
52 -)))|(((
53 -70ms
54 -)))
55 -|(((
56 -PREDICTION_STEP_SIZE
57 -)))|(((
58 -size of the steps for the forward search
59 -)))|(((
60 -10ms
61 -)))
62 -|(((
63 -REFINEMENT_FACTOR
64 -)))|(((
65 -The prediction step size for the reverse search is
66 -PREDICTION_STEP_SIZE divided by REFINEMENT_FACTOR.
67 -)))|(((
68 -10
69 -)))
17 +=== Flipper range ===
70 70  
71 -When setting the PREDICTION_FRAME keep in mind that predictions, that reach multiple frames into the future, are likely to be overwritten, when new frames arrive and new predictions are calculated.
72 -Nevertheless it is reasonable to calculate predictions beyond the next frame in case a ball is not recognized on the next frame.
19 +\\
73 73  
74 -With the default values up to 7 predictions are calculated if the ball is not predicted to be in flipper range roughly within the next two frames.
21 +\\
75 75  
76 -The REFINEMENT_FACTOR is also the worst case number of predictions calculated during the reverse search part of the prediction process.
23 +\\
77 77  
78 78  \\
79 79  
80 -=== Flipper range ===
27 +[[image:attach:physics2.png]]
81 81  
82 -The model of the area, where the the flippers can hit a ball is computed from a set of five points. These points are set to real world coordinates in meters
29 +\\
83 83  
84 -and should not need further adjustment after the camera is correctly calibrated (see [[doc:PP18.World Coordinate System]]).
31 +=== Inlane Area ===
85 85  
86 -The values for the left flipper are set to be symmetrical.
33 +[[image:attach:physics_inlane.png]]
87 87  
88 -[[image:attach:physics_points.png]]
35 +\\
89 89  
90 -(% class="wrapped" %)
91 -|=(((
92 -Point#
93 -)))|=(((
94 -Description
95 -)))
96 -|(((
97 -1
98 -)))|(((
99 -center point of the circle that the flippers tip moves o
100 -)))
101 -|(((
102 -2
103 -)))|(((
104 -highest point a ball can be at when it hits the resting flipper
105 -)))
106 -|(((
107 -3
108 -)))|(((
109 -lowest point a ball can be at when it hits the resting flipper
110 -)))
111 -|(((
112 -4
113 -)))|(((
114 -lowest point a ball can be at when it hits the fully triggered flipper
115 -)))
116 -|(((
117 -5
118 -)))|(((
119 -highest point a ball can be at when it hits the fully triggered flipper
120 -)))
37 +=== Prediction parameters ===
121 121  
122 122  \\
123 123  
124 -From these points an area, where the ball is deemed to be hittable, is computed.
41 +\\
125 125  
126 -[[image:attach:physics2.png]]
43 +\\
127 127  
128 128  \\
129 129  
130 -=== Inlane Area ===
47 +\\
131 131  
132 -Since the trajectory prediction does not consider collisions in general, we need a different kind of predictions for the inlanes,
133 -i.e. the path feeding a falling ball from the playfield to the flippers, behind the slingshot.
134 -A ball is considered to be in an inlane, when it is in a rectangular area, with one edge given by the beginning of the flipper
135 -and the other by a point at highest, outermost position of the angled part of the inlane.
49 +\\
136 136  
137 -In this area the vertical acceleration is deactivated in the prediction, since it would cause the prediction to assume the ball would slide into the wall.
138 -Though in reality there is still some acceleration, a simple linear prediction has shown to be practical in this less critical area.
51 +\\
139 139  
140 -[[image:attach:physics_inlane.png]]
53 +\\
54 +
55 +\\
Bildschirmfoto von 2020-03-07 12-21-22.png
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1 -71401594
1 +71401639
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1 -https://rtsys.informatik.uni-kiel.de/confluence//wiki/spaces/PP18/pages/71401594/Ball Physics
1 +https://rtsys.informatik.uni-kiel.de/confluence//wiki/spaces/PP18/pages/71401639/Ball Physics