Analysis Of Positioning Accuracy Research Articles

Full Positional Accuracy Analysis of Spatial Data by Means of Circular Statistics

AbstractThe positional error in spatial data is defined as a vector by comparing the coordinates between the true position and the measured position. The standard tests to assess the positional accuracy use only the magnitude of the vector and omit the azimuth. This article suggests that the use of both values allows a much more complete analysis of the positional error. A set of tests is proposed that are relevant for this purpose and demonstrate that some important features are not identified by the common procedures. The test samples come from two datasets. The first is obtained from the comparison of 100 homologous points in two conventional maps, and the second one comes from the geometric calibration of a photogrammetric scanner. The results are analyzed and discussed, showing that important issues such as error anisotropy are detected only by means of the circular statistics tests and density maps of distribution. Therefore, tests that assess the goodness of fit for uniform distribution in azimuths, such as Rayleigh and Rao tests, give low probabilities (P = 0 and P > 0.01). Moreover, density maps working with both magnitude and angle can locate the outlier candidate and offer more information about the spatial distribution of error.

LiDAR 데이터를 이용한 지형지물의 위치정확도 분석

본 연구에서는 연구지역을 대상으로 LiDAR(Light Detection And Ranging) 데이터와 항공사진, 수치 지도를 이용하여 지형지물에 대한 위치정확도 분석을 실시하였다. 연구지역은 부산광역시 사하구 하단지역으로 선정하였으며, 첨단 측량기법인 항공 LiDAR 데이터와 축척 1:20,000의 항공사진을 이용하였다. 그리고 각각의 영상에 대하여 표정작업과 영상의 재배열 과정을 거쳐 최종 수치정사영상을 제작하였다. 제작된 영상을 이용하여 검사점을 선정하고, 선정된 검사점에 대한 정보를 추출하였으며, 스크린 디지타이징기법을 통한 수평위치 좌표를 추출하였다. 그리고 국토지리 정보원에서 공시한 축척 1:5,000의 수치지도를 이용하여 추출된 LiDAR 데이터 좌표와 항공사진의 좌표를 각각 비교.분석하였다. 수치지도를 기준으로 비교 분석한 결과 항공사진의 수평위치 정확도가 항공 LiDAR 측량 성과 보다 건물의 경우 x방향으로 24cm, y방향으로 26cm정도가 우수함을 알 수 있었다. This study : An analysis of position accuracy of topography according to using LiDAR data, aerial photo and digital map for a study area was conducted. The study area was selected in Hadan area, Sahagu, Busan aerial LiDAR data and aerial photo in the scales of 1:20,000, which are high tech surveying ways were used. The final digital orthoimage according to orientation process for each image and image resampling was producted. Using it, a checkpoint was chosen, information about the checkpoints selected was extracted, a coordinate of Horizontal Position through the screen digitizing was also extracted. Both the coordinates of LiDAR data and aerial photo using digital map in the scales of 1:20,000 announced to the public from NGII(National Geographic Information Institute) were gradually compared and analyzed. Based on the digital map, as a result of being both compared and analyzed, it has shown to us that horizontal position of aerial photo is more accurate than that of aerial LiDAR surveying (RMSE-building x:24cm, y:26cm).

Off-axis alignment of an LDA-probe and the effect of astigmatism on measurements

A theoretical analysis of the positional accuracy of an LDA measurement volume using an off-axis alignment of a probe relative to an internal flow has been carried out. General performance parameters of measurements with a 1D-probe with an off-axis alignment are derived. In particular, the change in the fringe spacing, the relationship between the shift of the measurement volume and the probe movement, and the general 2-dimensional traversing properties of the measurement volume are considered. The displacement between the two LDA measurement volumes of a 2D-probe caused by astigmatism has been determined from exact calculations of the laser beam transmission. The benefits of a water-filled prism to ensure the coincidence of the measurement volumes and to reduce the effect of astigmatism on the data rate and the distortion of the measurement volume has been shown. A calculation procedure for the use of such a prism is given.