RotationVectorSensor.cpp revision 2cf098846c83bab82272f107ba110f7c47df1763 
1/*
2 * Copyright (C) 2010 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#include <stdint.h>
18#include <math.h>
19#include <sys/types.h>
20
21#include <utils/Errors.h>
22
23#include <hardware/sensors.h>
24
25#include "RotationVectorSensor.h"
26
27namespace android {
28// ---------------------------------------------------------------------------
29
30template <typename T>
31static inline T clamp(T v) {
32    return v < 0 ? 0 : v;
33}
34
35RotationVectorSensor::RotationVectorSensor(sensor_t const* list, size_t count)
36    : mSensorDevice(SensorDevice::getInstance()),
37      mALowPass(M_SQRT1_2, 1.5f),
38      mAX(mALowPass), mAY(mALowPass), mAZ(mALowPass),
39      mMLowPass(M_SQRT1_2, 1.5f),
40      mMX(mMLowPass), mMY(mMLowPass), mMZ(mMLowPass)
41{
42    for (size_t i=0 ; i<count ; i++) {
43        if (list[i].type == SENSOR_TYPE_ACCELEROMETER) {
44            mAcc = Sensor(list + i);
45        }
46        if (list[i].type == SENSOR_TYPE_MAGNETIC_FIELD) {
47            mMag = Sensor(list + i);
48        }
49    }
50    memset(mMagData, 0, sizeof(mMagData));
51}
52
53bool RotationVectorSensor::process(sensors_event_t* outEvent,
54        const sensors_event_t& event)
55{
56    const static double NS2S = 1.0 / 1000000000.0;
57    if (event.type == SENSOR_TYPE_MAGNETIC_FIELD) {
58        const double now = event.timestamp * NS2S;
59        if (mMagTime == 0) {
60            mMagData[0] = mMX.init(event.magnetic.x);
61            mMagData[1] = mMY.init(event.magnetic.y);
62            mMagData[2] = mMZ.init(event.magnetic.z);
63        } else {
64            double dT = now - mMagTime;
65            mMLowPass.setSamplingPeriod(dT);
66            mMagData[0] = mMX(event.magnetic.x);
67            mMagData[1] = mMY(event.magnetic.y);
68            mMagData[2] = mMZ(event.magnetic.z);
69        }
70        mMagTime = now;
71    }
72    if (event.type == SENSOR_TYPE_ACCELEROMETER) {
73        const double now = event.timestamp * NS2S;
74        float Ax, Ay, Az;
75        if (mAccTime == 0) {
76            Ax = mAX.init(event.acceleration.x);
77            Ay = mAY.init(event.acceleration.y);
78            Az = mAZ.init(event.acceleration.z);
79        } else {
80            double dT = now - mAccTime;
81            mALowPass.setSamplingPeriod(dT);
82            Ax = mAX(event.acceleration.x);
83            Ay = mAY(event.acceleration.y);
84            Az = mAZ(event.acceleration.z);
85        }
86        mAccTime = now;
87        const float Ex = mMagData[0];
88        const float Ey = mMagData[1];
89        const float Ez = mMagData[2];
90        float Hx = Ey*Az - Ez*Ay;
91        float Hy = Ez*Ax - Ex*Az;
92        float Hz = Ex*Ay - Ey*Ax;
93        const float normH = sqrtf(Hx*Hx + Hy*Hy + Hz*Hz);
94        if (normH < 0.1f) {
95            // device is close to free fall (or in space?), or close to
96            // magnetic north pole. Typical values are  > 100.
97            return false;
98        }
99        const float invH = 1.0f / normH;
100        const float invA = 1.0f / sqrtf(Ax*Ax + Ay*Ay + Az*Az);
101        Hx *= invH;
102        Hy *= invH;
103        Hz *= invH;
104        Ax *= invA;
105        Ay *= invA;
106        Az *= invA;
107        const float Mx = Ay*Hz - Az*Hy;
108        const float My = Az*Hx - Ax*Hz;
109        const float Mz = Ax*Hy - Ay*Hx;
110
111        // matrix to rotation vector (normalized quaternion)
112        float qw = sqrtf( clamp( Hx + My + Az + 1) * 0.25f );
113        float qx = sqrtf( clamp( Hx - My - Az + 1) * 0.25f );
114        float qy = sqrtf( clamp(-Hx + My - Az + 1) * 0.25f );
115        float qz = sqrtf( clamp(-Hx - My + Az + 1) * 0.25f );
116        qx = copysignf(qx, Ay - Mz);
117        qy = copysignf(qy, Hz - Ax);
118        qz = copysignf(qz, Mx - Hy);
119
120        // this quaternion is guaranteed to be normalized, by construction
121        // of the rotation matrix.
122
123        *outEvent = event;
124        outEvent->data[0] = qx;
125        outEvent->data[1] = qy;
126        outEvent->data[2] = qz;
127        outEvent->data[3] = qw;
128        outEvent->sensor = '_rov';
129        outEvent->type = SENSOR_TYPE_ROTATION_VECTOR;
130        return true;
131    }
132    return false;
133}
134
135status_t RotationVectorSensor::activate(void* ident, bool enabled) {
136    mSensorDevice.activate(this, mAcc.getHandle(), enabled);
137    mSensorDevice.activate(this, mMag.getHandle(), enabled);
138    if (enabled) {
139        mMagTime = 0;
140        mAccTime = 0;
141    }
142    return NO_ERROR;
143}
144
145status_t RotationVectorSensor::setDelay(void* ident, int handle, int64_t ns)
146{
147    mSensorDevice.setDelay(this, mAcc.getHandle(), ns);
148    mSensorDevice.setDelay(this, mMag.getHandle(), ns);
149    return NO_ERROR;
150}
151
152Sensor RotationVectorSensor::getSensor() const {
153    sensor_t hwSensor;
154    hwSensor.name       = "Rotation Vector Sensor";
155    hwSensor.vendor     = "Google Inc.";
156    hwSensor.version    = 1;
157    hwSensor.handle     = '_rov';
158    hwSensor.type       = SENSOR_TYPE_ROTATION_VECTOR;
159    hwSensor.maxRange   = 1;
160    hwSensor.resolution = 1.0f / (1<<24);
161    hwSensor.power      = mAcc.getPowerUsage() + mMag.getPowerUsage();
162    hwSensor.minDelay   = mAcc.getMinDelay();
163    Sensor sensor(&hwSensor);
164    return sensor;
165}
166
167// ---------------------------------------------------------------------------
168}; // namespace android
169
170