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Control Extension and Orthorectification Procedures for Compiling Vegetation 
Databases of National Parks in the Southeastern United States 
Thomas R. Jordan 
Center for Remote Sensing and Mapping Science (CRMS) 
Department of Geography, The University of Georgia Athens, GA 30602 USA 
tombob@uga.edu 
  
Commission IV, WG IV/6 
KEYWORDS: vegetation mapping; softcopy photogrammetry; GIS; mountainous terrain; national parks 
ABSTRACT: 
Vegetation mapping of national park units in the southeastern United States is being undertaken by the Center for Remote Sensing and 
Mapping Science at the University of Georgia. Because of the unique characteristics of the individual parks, including size, relief, 
number of photos and availability of ground control, different approaches are employed for converting vegetation polygons interpreted 
from large-scale color infrared aerial photographs and delineated on plastic overlays into accurately georeferenced GIS database layers. 
Using streamlined softcopy photogrammetry and aerotriangulation procedures, it is possible to differentially rectify overlays to 
compensate for relief displacements and create detailed vegetation maps that conform to defined mapping standards. This paper 
discusses the issues of ground control extension and orthorectification of photo overlays and describes the procedures employed in this 
project for building the vegetation GIS databases. 
INTRODUCTION 
The Center for Remote Sensing and Mapping Science (CRMS) 
at The University of Georgia has been engaged for several 
years in mapping vegetation communities in national parks in 
southeastern United States (Welch, et al, 2002). In this 
project, vegetation polygons delineated on overlays registered 
to large-scale (1:12,000 to 1:16,000 scale) color-infrared (CIR) 
aerial photographs are converted to digital format and 
integrated into a GIS database. To maximize vegetation 
discrimination, the aerial photographs are acquired during the 
autumn (leaf-on) season when the changing colors of the leaves 
provide additional indicators for species and vegetation 
community identification. It is critical that the polygons 
transferred from overlay to GIS database be accurate in terms 
of position, shape and size to ensure that analyses that depend 
on the interaction. of layered data sets, such as fire fuel 
modelling and data visualization, can be performed with 
confidence (Madden, 2004). As many of these parks are 
located in remote and rugged areas where conventional sources 
of ground control are lacking, streamlined aerotriangulation 
procedures have been developed to extend the existing ground 
control and permit the production of orthophotos and corrected 
overlays for incorporation into the GIS database. 
STUDY AREA AND METHODOLOGY 
The overall project area encompasses much of the southeastern 
United States and includes U.S. National Park units located in 
the states of Kentucky, Tennessee, North Carolina, South 
Carolina, Virginia and Alabama (Figure 1). The parks differ 
greatly in size, location, relief and origin. Some of the smaller 
(100-400 ha) historical battlefield parks and national home sites 
in the project are located in or near urban areas with little relief 
and ample roads, field boundaries and other features that can be 
657 
used for ground control. In these cases, ground control 
coordinates are extracted from U.S. Geological Survey (USGS) 
Digital Orthophoto Quarter Quadrangles (DOQQ) and simple 
polynomial techniques are applied to create corrected photos. 
Interpretation is then performed directly on the rectified CIR 
photographs and the polygons transferred into the GIS. 
  
    
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Figure 1. U.S. National Park units being mapped by the UGA - 
CRMS. See Table 1 below for park name abbreviations. 
Many of the parks, however, are set aside to protect natural 
areas ranging from 80 to over 2000 sq. km in size and require a 
large number of aerial photographs for complete coverage 
(Table 1). In the more remote areas, a recurring problem is the 
lack of cultural features suitable for use as the ground control 
required to restitute the aerial photographs and associated 
overlays. This issue is frequently exacerbated by the presence 
of extensive forest cover and high relief. The result is that the 
locations and shapes of vegetation polygons interpreted for