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
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
|
# SPDX-License-Identifier: LGPL-2.1-or-later
#
# Copyright (C) 2019, Google Inc.
#
%YAML 1.2
---
controls:
- Location:
type: int32_t
description: |
Camera mounting location
enum:
- name: CameraLocationFront
value: 0
description: |
The camera is mounted on the front side of the device, facing the
user
- name: CameraLocationBack
value: 1
description: |
The camera is mounted on the back side of the device, facing away
from the user
- name: CameraLocationExternal
value: 2
description: |
The camera is attached to the device in a way that allows it to
be moved freely
- Rotation:
type: int32_t
description: |
The camera rotation is expressed as the angular difference in degrees
between two reference systems, one relative to the camera module, and
one defined on the external world scene to be captured when projected
on the image sensor pixel array.
A camera sensor has a 2-dimensional reference system 'Rc' defined by
its pixel array read-out order. The origin is set to the first pixel
being read out, the X-axis points along the column read-out direction
towards the last columns, and the Y-axis along the row read-out
direction towards the last row.
A typical example for a sensor with a 2592x1944 pixel array matrix
observed from the front is
2591 X-axis 0
<------------------------+ 0
.......... ... ..........!
.......... ... ..........! Y-axis
... !
.......... ... ..........!
.......... ... ..........! 1943
V
The external world scene reference system 'Rs' is a 2-dimensional
reference system on the focal plane of the camera module. The origin is
placed on the top-left corner of the visible scene, the X-axis points
towards the right, and the Y-axis points towards the bottom of the
scene. The top, bottom, left and right directions are intentionally not
defined and depend on the environment in which the camera is used.
A typical example of a (very common) picture of a shark swimming from
left to right, as seen from the camera, is
0 X-axis
0 +------------------------------------->
!
!
!
! |\____)\___
! ) _____ __`<
! |/ )/
!
!
!
V
Y-axis
With the reference system 'Rs' placed on the camera focal plane.
¸.·˙!
¸.·˙ !
_ ¸.·˙ !
+-/ \-+¸.·˙ !
| (o) | ! Camera focal plane
+-----+˙·.¸ !
˙·.¸ !
˙·.¸ !
˙·.¸!
When projected on the sensor's pixel array, the image and the associated
reference system 'Rs' are typically (but not always) inverted, due to
the camera module's lens optical inversion effect.
Assuming the above represented scene of the swimming shark, the lens
inversion projects the scene and its reference system onto the sensor
pixel array, seen from the front of the camera sensor, as follow
Y-axis
^
!
!
!
! |\_____)\__
! ) ____ ___.<
! |/ )/
!
!
!
0 +------------------------------------->
0 X-axis
Note the shark being upside-down.
The resulting projected reference system is named 'Rp'.
The camera rotation property is then defined as the angular difference
in the counter-clockwise direction between the camera reference system
'Rc' and the projected scene reference system 'Rp'. It is expressed in
degrees as a number in the range [0, 360[.
Examples
0 degrees camera rotation
Y-Rp
^
Y-Rc !
^ !
! !
! !
! !
! !
! !
! !
! !
! 0 +------------------------------------->
! 0 X-Rp
0 +------------------------------------->
0 X-Rc
X-Rc 0
<------------------------------------+ 0
X-Rp 0 !
|
