8
January 2019
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
A N I N T E R V I E W
What motivated the new edition of the “The DEM
User Manuel”?
Whenever I autograph a copy of the DEM Users Manual,
I write “May all your DEMs come true!” This is an obvious
play on words with “May all your dreams come true.” When
the 2
nd
edition was published, I had three basic dreams:
1.
Development of high-accuracy, affordable elevation
technologies for the betterment of society
2.
Development and update of DEM technology standards,
guidelines and specifications, and
3.
Implementation of a nationwide program, such as to-
day’s 3D Elevation Program (3DEP), to produce and
maintain standardized high-quality DEMs used by all.
These first three dreams have largely been realized, as doc-
umented in this 3
rd
edition. My future dreams include:
4.
Development of a seamless 3D Nation from the tops of
the mountains to the depths of the seas, to include in-
land bathymetry
5.
Use of the latest elevation data to routinely and sys-
tematically update the National Hydrography Dataset
(NHD), flood studies, forest metrics and other datasets
that require up-to-date topographic and bathymetric
DEMs, and
6.
Development of DEM applications to fully support the
dozens of business uses and hundreds of mission-criti-
cal activities (MCAs) documented in the National En-
hanced Elevation Assessment (NEEA) study published
in 2012 and the 3D Nation Requirements and Benefits
Study being conducted in 2018-2019.
The focus of this 3
rd
edition of the DEM Users Manual is to
help make all of these dreams come true.
Is there recent progress in the production of
digital elevation models ASPRS members should
note?
Over the past decade, technologies have matured, and much
progress has been made towards standardization:
•
In 2010, the U.S. Geological Survey (USGS) published
its draft Lidar Guidelines and Base Specifications,
V.13, which ultimately became the USGS Lidar Base
Specification, V1.0.
•
In 2012, the NEEA study was published that provided
a comprehensive analysis of DEM user requirements
and benefits for five Quality Levels (QLs) of topograph-
ic DEMs.
•
In 2012, USGS published its Lidar Base Specification,
V1.0.
•
In 2013, based on the NEEA implementation scenar-
io with the highest return-on-investment, USGS an-
nounced the new 3DEP to deliver QL2 lidar nationwide
except for QL5 IfSAR statewide in Alaska.
•
In 2013, ASPRS published its latest LAS Specification,
V1.4.
datum to another.
Figure 7 (right) is an
image from Chapter
2 that explains the
difference between
orthometric heights,
ellipsoid
heights,
and geoid undula-
tions.
Chapter 3—Standards, Guidelines and Specifications
introduces DEM
users to the ASPRS Positional Accuracy Standards for Digital Geospatial Data
v1.0, the ASPRS LAS Specifications v1.4, the USGS Lidar Base Specifications
v1.3, the National Ocean Service (NOS) Hydrographic Survey Specifications
based on standards of the International Hydrographic Organization (IHO), and
other relevant standards, guidelines and specifications. It is important that
DEM users understand these documents and how they must be rigorously en-
forced to achieve our vision of a seamless, consistent, high-accuracy, high-res-
olution 3D Nation, from the tops of the mountains to the depths of the sea.
Chapter 4—The National Elevation Datase–NED
provides the back-
ground, rationale and history of the legacy NED and how NED data were pro-
duced, quality controlled and delivered to the public. It provides information
about NED specifications and production processing, accuracy and data quali-
ty. The NED was retired when the 3DEP became operational, but USGS is de-
veloping a new line of science
products known as the Coastal
National Elevation Database
(CoNED) which integrates re-
cent high resolution coastal li-
dar data (both topographic and
bathymetric) and a temporal
component from captures on
different dates. An example of
a CoNED dataset is shown at
Figure 8 (right).
Chapter 5—The 3D Elevation Program–3DEP
explains USGS’ national
elevation initiative that forms the elevation layer of The National Map. The
3DEP resulted from analyses and vetting of the NEEA study which assessed
