PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
March 2015
173
New Standard for New Era: Overview
of the 2015 ASPRS Positional Accuracy
Standards for Digital Geospatial Data
The new ASPRS accuracy standards fill a critical need,
vital for map users and 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 vs.
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.
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 with those standards and current
mapping methodologies. The ASPRS 1990 Standards
were an improvement over NMAS; however, they do
not well represent the capabilities of lidar, orthoimagery,
digital mapping cameras or other current technologies in
wide-spread 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, but it 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.
The new ASPRS Positional Accuracy Standards for
Digital Geospatial Data address recent innovations in
digital imaging and non-imaging sensors, airborne GPS,
inertial measurement unit (IMU) and aerial triangulation
(AT) technologies. Unlike prior standards, the new
standards are independent of scale and contour interval,
they address the higher level of accuracies achievable by
the latest technologies (e.g. unmanned aerial systems and
lidar mobile mapping systems), and they provide enough
flexibility to be applicable to future technologies as they
are developed. Finally, the new standards provide cross
references to older standards, as well as detailed guidance
for a wide range of potential applications.
I
ntroduction
Effective in November, 2014, the
ASPRS Positional Accuracy Standards for Digital
Geospatial Data
(2014) replaced the
ASPRS Accuracy Standards for Large-Scale
Maps
(1990) and the
ASPRS Guidelines, Vertical Accuracy Reporting for Lidar Data
(2004). This standard was developed by the ASPRS Map Accuracy Standards Working
Group, a joint committee under the Photogrammetric Applications Division, Primary
Data Acquisition Division and Lidar Division, which was 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 on November 17, 2014. The new standard
is available at:
: the ASPRS Standards
web page. Readers can then navigate to the
ASPRS Positional Accuracy Standards for
Digital Geospatial Data
.
Developed to address current technologies, this standard includes positional accuracy
standards for digital orthoimagery, digital planimetric data, and digital elevation data. The
standard follows metric measurement units to make it consistent with the international
standards and practices. Accuracy classes, based on RMSE values, have been revised
and upgraded from the 1990 standard to address the higher accuracies achievable with
newer technologies. The standard also includes additional accuracy measures, such as
orthoimagery seam lines, ground control accuracy, aerial triangulation accuracy, lidar
relative swath-to-swath accuracy, recommended minimum Nominal Pulse Density
(NPD), horizontal accuracy of elevation data, delineation of low confidence areas for
vertical data, horizontal accuracy for elevation data, and the required number and spatial
distribution of check points based on project area.
The standard addresses geo-location accuracies of geospatial products, and it is not
intended to cover classification accuracy of thematic maps. Further, the standard does
not specify the best practices or methodologies needed to meet the accuracy thresholds
stated herein. The standard is intended to be used by geospatial data providers and users
to specify the positional accuracy requirements for final geospatial products and to
report data accuracies.
The standard defines accuracy classes based on RMSE thresholds for digital
orthoimagery, digital planimetric data, and digital elevation data. It is limited in scope
to addressing accuracy thresholds and testing methodologies for the most common
mapping applications and to meet immediate shortcomings in the outdated 1990 and
2004 standards referenced above. The standard is intended to be technology independent
and broad based, recognizing that limitations remain. It is intended to be the initial
component upon which future work can build. Additional supplemental standards or
modules should be pursued and added by subject matter experts in these fields as they
are developed and approved by the ASPRS.
Visit
to view the new standards in its entirety.
