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EXTRACTING HIGH RESOLUTION DIGITAL ELEVATION MODELS AND 
FEATURES IN A SOFTCOPY ENVIRONMENT 
Charles K. Toth and Andre Templer 
Center for Mapping 
Department of Geodetic Science and Surveying 
The Ohio State University 
1216 Kinnear Road, Columbus, OH 43212-1154 
e-mail: toth(a)cfm.ohio-state.edu 
USA 
Commission III 
KEY WORDS: DEM/DTM, Feature Extraction, Softcopy Experiences, Urban Imagery 
ABSTRACT 
Digital elevation models play an essential role in many mapping and engineering applications. With the 
introduction of softcopy systems, new technologies are available for both manual and automated DTM 
extraction and feature collection. This paper reports our experiences with softcopy systems and compares 
their performance and results to the traditional analytical plotter-based methods. The objective of our project 
was to test the feasibility of new softcopy DTM and feature extraction techniques for high density urban and 
suburban areas. 
Traditionally, DTMs and features are extracted from "hard copy" aerial images on analytical stereoplotters. 
This process is supported by specialized photogrammetric software for image orientation, data extraction, 
and input to GIS-type database. Our approach used a softcopy photogrammetric workstation and digital aerial 
images. The images were obtained by scanning aerial diapositives at a nominal resolution of 25 micrometers 
on a Leica scanner. All the tests, including orientation and data extraction, were carried out on a 
Leica/Helava DPW 770 softcopy workstation.' 
1. INTRODUCTION 
New, emerging technologies often require a large 
volume of spatial data in an unconventional format. 
A typical example is the construction of cellular 
phone networks. In order to determine the optimal 
distribution of cells, i.e., where to build the radio 
transmitter stations, a careful spatial analysis is 
necessary to assess and model the electromagnetic 
signal propagation in the area. This process 
frequently requires an unusually dense 
representation of the surface including all natural 
and man-made objects. Furthermore, a key element 
of this data is the surface normal since signal 
reflections play a very important role in the analysis 
of the electromagnetic field. This necessitates a sub- 
meter grid representation of the area including 
terrain points, buildings, transportation structures, 
tree canopies, etc. This "draped" surface data is the 
  
primary input to the electromagnetic signal 
propagation analysis program which is built around 
a ray tracing algorithm. Different antenna positions 
are analyzed in order to arrive at the optimal antenna 
location. In an additional step, traditional GIS data 
about the usage of the cellular phones, such as the 
population demographics, traffic, and behavioral 
patterns are considered to analyze the capacity 
conditions and finalize the antenna positions. The 
currency of the data and quick turnaround times are 
also important aspects. 
In cooperation with a cellular phone company, a 
pilot project was carried out at the Center for 
Mapping and the Department of Geodetic Science 
and Surveying in 1995. The objective was to deliver 
Im grid data covering the combined surface of 
natural and man-made objects over two very dense 
urban areas with sizes of approximately 2km by 
! The Leica/Helava DPW 770 softcopy system was donated to the Department of Geodetic Science and Surveying, The Ohio State 
University, by Leica Inc. in 1995. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B3. Vienna 1996