ardupilot/libraries/AP_OpticalFlow/AP_OpticalFlow.cpp

/*
	ADC.cpp - Analog Digital Converter Base Class for Ardupilot Mega
	Code by James Goppert. DIYDrones.com

	This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
    License as published by the Free Software Foundation; either
    version 2.1 of the License, or (at your option) any later version.
*/

#include "AP_OpticalFlow.h"

#define FORTYFIVE_DEGREES 0.78539816

AP_OpticalFlow::AP_OpticalFlow() : raw_dx(0),raw_dy(0),x(0),y(0),surface_quality(0),dx(0),dy(0),last_update(0),field_of_view(1),scaler(0),num_pixels(0)
{
}

// init - initCommAPI parameter controls whether I2C/SPI interface is initialised (set to false if other devices are on the I2C/SPI bus and have already initialised the interface)
bool 
AP_OpticalFlow::init(bool initCommAPI)
{
    _orientation_matrix = Matrix3f(1,0,0,0,1,0,0,0,1);
    update_conversion_factors();
    return true;  // just return true by default
}

// set_orientation - Rotation vector to transform sensor readings to the body frame.
void
AP_OpticalFlow::set_orientation(const Matrix3f &rotation_matrix)
{
    _orientation_matrix = rotation_matrix;
}

// read latest values from sensor and fill in x,y and totals
int AP_OpticalFlow::read()
{
}

// reads a value from the sensor (will be sensor specific)
byte 
AP_OpticalFlow::read_register(byte address)
{
}

// writes a value to one of the sensor's register (will be sensor specific)
void 
AP_OpticalFlow::write_register(byte address, byte value)
{
}

// rotate raw values to arrive at final x,y,dx and dy values
void 
AP_OpticalFlow::apply_orientation_matrix()
{
    Vector3f rot_vector;
	
	// next rotate dx and dy
	rot_vector = _orientation_matrix * Vector3f(raw_dx,raw_dy,0);
	dx = rot_vector.x;
	dy = rot_vector.y;
	
	// add rotated values to totals (perhaps this is pointless as we need to take into account yaw, roll, pitch)
	x += dx;
	y += dy;
}

// updatse conversion factors that are dependent upon field_of_view
void
AP_OpticalFlow::update_conversion_factors()
{
    conv_factor = (1.0/(float)(num_pixels*scaler))*2.0*tan(field_of_view/2.0);  // multiply this number by altitude and pixel change to get horizontal move (in same units as altitude)
    radians_to_pixels = (num_pixels*scaler) / field_of_view;
}

// updates internal lon and lat with estimation based on optical flow
void
AP_OpticalFlow::get_position(float roll, float pitch, float yaw, float altitude)
{
    float diff_roll = roll - _last_roll;
    float diff_pitch = pitch - _last_pitch;
	float avg_altitude = (altitude + _last_altitude)/2;
    //float exp_change_x, exp_change_y;
    //float change_x, change_y;
	//float x_cm, y_cm;
	float cos_yaw = cos(yaw);
	float sin_yaw = sin(yaw);
    int i;
    
	// only update position if surface quality is good and angle is not over 45 degrees
	if( surface_quality >= 10 && fabs(roll) <= FORTYFIVE_DEGREES && fabs(pitch) <= FORTYFIVE_DEGREES ) {
		// calculate expected x,y diff due to roll and pitch change
		exp_change_x = diff_roll * radians_to_pixels;
		exp_change_y = -diff_pitch * radians_to_pixels;
			
		// real estimated raw change from mouse
		change_x = dx - exp_change_x;
		change_y = dy - exp_change_y;

		// convert raw change to horizontal movement in cm
		x_cm = -change_x * avg_altitude * conv_factor;    // perhaps this altitude should actually be the distance to the ground?  i.e. if we are very rolled over it should be longer?
		y_cm = -change_y * avg_altitude * conv_factor;    // for example if you are leaned over at 45 deg the ground will appear farther away and motion from opt flow sensor will be less
		
		// use yaw to convert x and y into lon and lat
		lat += y_cm * cos_yaw - x_cm * sin_yaw;
		lng += x_cm * cos_yaw + y_cm * sin_yaw;
	}
	
    // capture roll and pitch for next iteration
    _last_roll = roll;
    _last_pitch = pitch;
	_last_altitude = altitude;
}