In November 2014, the American Society for Photogrammetry and Remote Sensing (ASPRS) released an updated standard, Positional Accuracy Standards for Digital Geospatial Data, to tie together past experience with current industry practice of preparing data, but not plotting the resulting maps. The new standard provides guidelines for calculating both the vertical and the horizontal accuracy. Prior standards include the National Map Accuracy Standards (NMAS), which were developed in 1947, the 1990 ASPRS Accuracy Standards for Large-Scale Maps Standards and 2004 ASPRS Guidelines, Vertical Accuracy Reporting for Lidar Data. None of the previous standards was designed to address the current technologies available for LIDAR, orthoimagery or digital camera mapping. The 2014 ASPRS Standards, were therefore created to help address the new technology. The new standards focus on the higher level of accuracy that are currently available using the latest technology.
A portion of the updated 2014 ASPRS Standards addresses horizontal accuracy. Horizontal accuracy requires a known position (an identifiable marker) that is clearly defined within the data itself. For most airborne LIDAR data, the data is simply not dense enough to get any kind of clear features. Mobile and terrestrial LIDAR data, as well as photogrammetric elevation data and orthoimagery, can be readily used in a horizontal accuracy assessment. While the measurement and reporting of horizontal accuracies for airborne LIDAR data was removed from the final ASPRS Positional Accuracy Standards we have a seen a growing trend in the industry for a measured result as opposed to the estimated accuracy, based upon manufacturer’s guidelines and the LIDAR Horizontal Error (Figure 1), that traditionally has accompanied a delivered airborne LIDAR dataset.