New positional accuracy standards for digital geospatial data have been released by the U.S.-based international organization for geospatial information professionals.
Announced this week by the American Society of Photogrammetry and Remote Sensing (ASPRS), the new accuracy standards fill a critical need for map users and map makers alike. For centuries, map scale and contour interval have been used as an indication of map accuracy. Users want to know how accurately they can measure different things on a map, and map makers want to know how accurate maps need to be in order to satisfy user requirements. Those contracting for new maps depend on some form of map accuracy standard to evaluate the tradeoff between the accuracy required versus how much time and expense are justified in achieving it, and then to describe the accuracy of the result in a uniform way that is reliable, defensible and repeatable.
The new ASPRS standards address recent innovations in digital imaging and non-imaging sensors, airborne GPS, inertial measurement units and aerial triangulation technologies. Unlike prior standards, the new standards are independent of scale and contour interval, they address higher levels of accuracies achievable by the latest technologies such as unmanned aerial systems and LiDAR mobile mapping systems, and they provide enough flexibility to be applicable to future technologies as they are developed. Furthermore, the new standards provide cross-references to older standards, as well as detailed guidance for a wide range of potential applications.
According to ASPRS, no prior U.S. accuracy standard comprehensively addresses the current state of mapping technology, which is why the new ASPRS standards were developed. The National Map Accuracy Standards (NMAS), developed in 1947, are still used because they are simple, but there is no scientific correlation between those standards and current mapping methodologies. The ASPRS 1990 Standards were a claimed improvement over NMAS; however, they did not do well in representing the capabilities of LiDAR, orthoimagery, digital mapping cameras or other current technologies in widespread use today. The National Standard for Spatial Data Accuracy (NSSDA) is a reporting standard that references the old ASPRS 1990 standards and is cross-referenced in the new ASPRS standards. NSSDA provides no accuracy thresholds, and does not by itself provide any new or updated guidance on how to select or specify an appropriate accuracy for intended applications, says ASPRS.
The new ASPRS standards were developed by the ASPRS Map Accuracy Standards Working Group, a joint committee under the Photogrammetric Applications Division, Primary Data Acquisition Division and LiDAR Division, formed for the purpose of reviewing and updating ASPRS map accuracy standards to reflect current technologies. A subcommittee of this group, consisting of Dr. Qassim Abdullah, Dr. David Maune, Doug Smith and Hans Karl Heidemann, was responsible for drafting the document. Draft versions of the standard underwent extensive review, both within ASPRS as well as through public review by other key geospatial mapping organizations, prior to final approval by the ASPRS Board of Directors this past Nov. 17.
Founded in 1934, ASPRS is devoted to advancing knowledge and improving understanding of the mapping sciences to promote responsible application of photogrammetry, remote sensing, geographic information systems and supporting technologies.