Độ chính xác được sử dụng để thể hiện mức độ gần gũi của một đo lường, hoặc giải pháp thu được, với giá trị thực sự. Độ chính xác hạn, tuy nhiên, được sử dụng để mô tả mức độ gần gũi của các phép đo lặp đi lặp lại cùng số lượng với nhau. Trong trường hợp không có lỗi hệ thống, chính xác và độ chính xác sẽ được tương đương với [1]. Vì lý do này, hai thuật ngữ được sử dụng bừa bãi trong nhiều mục đích thiết thực. Độ chính xác có thể được. | Appendix A GPS Accuracy and Precision Measures The term accuracy is used to express the degree of closeness of a measurement or the obtained solution to the true value. The term precision however is used to describe the degree of closeness of repeated measurements of the same quantity to each other. In the absence of systematic errors accuracy and precision would be equivalent 1 . For this reason the two terms are used indiscriminately in many practical purposes. Accuracy can be measured by a statistical quantity called the standard deviation assuming that the GPS measurements contain no systematic errors or blunders. The lower the standard deviation the higher the accuracy. For the 1-D case for example measuring the length of a line between two points the accuracy is expressed by the so-called root mean square rms . The rms is associated with a probability level . For example the accuracy of the static GPS surveying could be expressed as 5 mm 1 ppm rms . This means that there is a chance or probability that we get an error of less than or equal to 5 mm 1 mm for every kilometer. In other words if we measure a 10-km baseline then there is a 161 162 Introduction to GPS chance that we get an error of less than or equal to 15 mm in the measured line. Horizontal component . easting and northing accuracy a 2-D case is expressed by either the circular error probable CEP or twice distance rms 2drms . CEP means that there is a 50 chance that the true horizontal position is located inside a circle of radius equal to the value of CEP 1 . The corresponding probability level of the 2drms varies from to depending on the relative values of the errors in the easting and northing components. The ratio of the 2drms to the CEP varies from to 3. This means that an accuracy of 40m CEP is equivalent to 100m 2drms for a ratio of . The spherical error probable SEP is used to express the accuracy of the 3-D case. SEP means that there is a 50 chance that
