為人熟知的GPS定位只適合用於戶外，倘若受到建築物遮蔽，GPS定位效果將大打折扣。然而室內環境是人們生活和工作的主要場所。統計數據[1]顯示，大多數人大約80%-90%的時間都在室內環境中度過。隨著室內環境越來越複雜，室內定位將為人們的生活提供極大的便利，尤其是在商場、停車場、車站、機場等複雜的室內環境中。此外，室內定位還可以為商業客戶提供大量數據、為人們提供更好的服務。
本論文提出基於地球磁場的定位系統，只需要靠智慧型行動裝置搭載之慣性測量單元（Inertial Measurement Unit, IMU）直接收集磁場資料以及方向，透過四元數旋轉矩陣校正後，將局部座標轉換成全局座標（local coordinate to global coordinate），接著把xyz三軸及合力（又稱磁場強度intensity）連接成磁指紋，再加入標準差作為特徵，存進資料庫；定位當下將收到的磁場資料即時計算成磁指紋後與資料庫比對，求餘弦相似性（cosine similarity）最高者為定位結果，搭配有向圖（Directed Acyclic Graph, DG）的概念限縮可能的定位範圍，以此進一步提升準確度、降低誤差。
室內定位系統最常面臨的問題與所提方法的應對彙整如下：
- 訊號不穩定：透過旋轉矩陣將局部座標轉換成全局座標。
- 需建置基礎設施：IMU即可收集資料，無需事先架設任何硬體設備。
- 高維護成本：磁場雖會隨著時間變化，但整體屬於相對穩定，大約每5年重新收一次資料即可。
- 需穩定的網路品質：因有建立磁指紋資料庫，使用者可以預先下載資料，之後即便網路不穩也不影響使用者端直接使用IMU收集資料，以及裝置運算、比對磁指紋。如果有穩定的網路，使用者也可以選擇全線上操作，後台記錄的資料會被發送到伺服器以獲得定位。
本論文於臺灣科技大學電資學院7、8樓進行測試，以點對點比對的方式定位，綜合所有實驗結果得出之最大誤差約5.35 m，最小誤差0.0 m，平均誤差約1 m以內。

The GPS positioning is only suitable for outdoor use, and its performance will be greatly reduced if it is obscured by buildings. However, the indoor environment is the main place where people live and work. Statistics show that most people spend about 80%-90% of their time in indoor environments (see literature). As indoor environments become more and more complex, indoor positioning will provide great convenience to people's lives, especially in complex indoor environments such as shopping malls, parking lots, stations, and airports.
In this paper, we propose a positioning system based on the earth's magnetic field, which only relies on the inertial measurement unit (IMU) to directly collect the magnetic field data and directions, and then converts the local coordinate to global coordinate by quaternion rotational matrix. Then, the magnetic field data are connected into magnetic fingerprints, and the standard deviation is added as a feature and stored in the database. When positioning, the received magnetic field data are calculated into magnetic fingerprints immediately and compared with the database to find the one that has the highest cosine similarity as the positioning result. With the concept of directed graph (DG), we could limit the possible positioning range, this is to further improve the accuracy and reduce the error.
The most common problems faced by indoor positioning systems and the proposed solutions are summarized as follows:
 Signal instability: Conversion of local coordinates to global coordinates by rotating the matrix.
 Need to build infrastructure in advance: IMU can collect data without setting up any hardware beforehand.
 High maintenance cost: Although the magnetic field changes over time, it is relatively stable overall, so it is sufficient to recollect every 5 years.
 Stable network quality: With the establishment of a magnetic fingerprint database, users can download data in advance, even if the network is unstable, users still can collect data using IMU directly, and then compute and compare magnetic fingerprints with the device. If there is a stable network, users can also choose to operate fully online, and the data recorded in the backend will be sent to the server for positioning.
The paper was tested on the 7th and 8th floors of the College Electrical Engineering and Computer Science (CEECS) of National Taiwan University of Science and Technology (NTUST) by point-to-point comparison, the maximum error of the experimental results is about 5.35 m, the minimum error is 0.0 m, and the average error is less than 1 m. 

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