1 /* 2 * Copyright (C) 2016 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 ////////////////////////////////////////////////////////////////////////////// 18 /* 19 * This function implements a diversity checker and stores diverse vectors into 20 * a memory. We assume that the data is located on a sphere, and we use the 21 * norm of the difference of two vectors to decide if the vectors are diverse 22 * enough: 23 * 24 * k = norm( v1 - v2 )^2 < Threshold 25 * 26 * Hence when k < Threshold the data is not stored, because the vectors are too 27 * similar. We store diverse vectors in memory and all new incoming vectors 28 * are checked against the already stored data points. 29 * 30 * Furthermore we also check if k > max_distance, since that data is most likely 31 * not located on a sphere anymore and indicates a disturbance. Finally we give 32 * a "data is full" flag to indicate once the memory is full. 33 * The diverse data can be used to improve sphere fit calibrations, ensuring 34 * that the sphere is populated enough resulting in better fits. 35 * 36 * Memory is stored in an array initialized to length of 37 * [THREE_AXIS_DATA_DIM * NUM_DIVERSE_VECTORS], this has been done to be 38 * compatible with the full sphere fit algorithm. 39 * 40 * Notice, this function stops to check if data is diverse, once the memory is 41 * full. This has been done in order to save processing power. 42 */ 43 44 #ifndef LOCATION_LBS_CONTEXTHUB_NANOAPPS_CALIBRATION_COMMON_DIVERSITY_CHECKER_H_ 45 #define LOCATION_LBS_CONTEXTHUB_NANOAPPS_CALIBRATION_COMMON_DIVERSITY_CHECKER_H_ 46 47 #include <stdbool.h> 48 #include <stddef.h> 49 #include <stdint.h> 50 51 #ifdef __cplusplus 52 extern "C" { 53 #endif 54 55 #define THREE_AXIS_DATA_DIM (3) // data is three-dimensional. 56 #define NUM_DIVERSE_VECTORS (20) // Storing 20 data points. 57 58 // Main data struct. 59 struct DiversityChecker { 60 // Data memory. 61 float diverse_data[THREE_AXIS_DATA_DIM * NUM_DIVERSE_VECTORS]; 62 63 // Number of data points in the memory. 64 size_t num_points; 65 66 // Number of data points that violated the max_distance condition. 67 size_t num_max_dist_violations; 68 69 // Threshold value that is used to check k against. 70 float threshold; 71 72 // Threshold tuning paramter used to calculate threshold (k_algo): 73 // threshold = threshold_tuning_param_sq * (local_field)^2. 74 float threshold_tuning_param_sq; 75 76 // Maximum distance value. 77 float max_distance; 78 79 // Max Distance tuning parameter: 80 // max_distance = max_distance_tuning_param_sq * (local_field)^2. 81 float max_distance_tuning_param_sq; 82 83 // Data full bit. 84 bool data_full; 85 86 // Setup variables for NormQuality check. 87 88 size_t min_num_diverse_vectors; 89 size_t max_num_max_distance; 90 float var_threshold; 91 float max_min_threshold; 92 }; 93 94 // Initialization of the function/struct, input: 95 // min_num_diverse_vectors -> sets the gate for a minimum number of data points 96 // in the memory 97 // max_num_max_distance -> sets the value for a max distance violation number 98 // gate. 99 // var_threshold -> is a threshold value for a Norm variance gate. 100 // max_min_threshold -> is a value for a gate that rejects Norm variations 101 // that are larger than this number. 102 // local_field -> is the assumed local_field (radius of the sphere). 103 // threshold_tuning_param -> threshold tuning parameter used to calculate 104 // threshold (k_algo). 105 // max_distance_tuning_param -> Max distance tuning parameter used to calculate 106 // max_distance. 107 void diversityCheckerInit(struct DiversityChecker* diverse_data, 108 size_t min_num_diverse_vectors, 109 size_t max_num_max_distance, float var_threshold, 110 float max_min_threshold, float local_field, 111 float threshold_tuning_param, 112 float max_distance_tuning_param); 113 114 // Resetting the memory and the counters, leaves threshold and max_distance 115 // as well as the setup variables for NormQuality check untouched. 116 void diversityCheckerReset(struct DiversityChecker* diverse_data); 117 118 // Main function. Tests the data (x,y,z) against the memory if diverse and 119 // stores it, if so. 120 void diversityCheckerUpdate(struct DiversityChecker* diverse_data, float x, 121 float y, float z); 122 123 // Removing a constant bias from the diverse_data and check if the norm is 124 // within a defined bound: 125 // implemented 4 gates 126 // -> needs a minimum number of data points in the memory 127 // (controlled by min_num_divers_vectors). 128 // -> will return false if maximum number of max_distance is reached 129 // (controlled by max_num_max_distance). 130 // -> norm must be within a var window. 131 // -> norm must be within a MAX/MIN window. 132 // Returned value will only be true if all 4 gates are passed. 133 bool diversityCheckerNormQuality(struct DiversityChecker* diverse_data, 134 float x_bias, 135 float y_bias, 136 float z_bias); 137 138 // This function updates the threshold value and max distance value based on the 139 // local field. This ensures a local field independent operation of the 140 // diversity checker. 141 // 142 // threshold = (threshold_tuning_param * local_field)^2 143 // max_distance = (max_distance_tuning_param * local_field)^2 144 void diversityCheckerLocalFieldUpdate(struct DiversityChecker* diverse_data, 145 float local_field); 146 #ifdef __cplusplus 147 } 148 #endif 149 150 #endif // LOCATION_LBS_CONTEXTHUB_NANOAPPS_CALIBRATION_COMMON_DIVERSITY_CHECKER_H_ 151
