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|. 23, No. 21,
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Ali, Mahmoud El Nokrashy
ACCURACY ANALYSIS FOR NEW CLOSE-RANGE
PHOTOGRAMMETRIC SYSTEMS
Dr. Mahmoud El-Nokrashy O. ALI Dr. Mohamed Ashraf ELIWA
Prof. of Photogrammetry, Civil Eng. Associate Prof. of Geodesy, Civil Eng
Al Azhar University, Cairo, Egypt Minia University, Minia, Egypt.
m_ali@starnet.com.eg
Dr. Ahmed Abd-Elreheem MOHAMMED Eng. Abbas Mohammed ABBAS
Associate Prof. of Photogrammetry, Civil Eng. Lecturer Assistant, Civil Eng.
Assuit University, Assuit, Egypt Minia University, Minia, Egypt.
Working Group V/1
KEY WORDS: Close Range Photogrammetry, Accuracy Evaluation, Mobile Mapping System.
ABSTRACT
Mobile mapping system is a close range photogrammetric system proved to be useful in many GIS applications.
Whenever an area needs to be surveyed, a van equipped with all the necessary instruments and sensors travels into that
area and takes a series of images of the objects and collects other information related to each images. The data is
displayed on the workstation monitor. Through the interaction, the operator can measure all of the objects that appear in
multiple images and subsequently calculate and store 3D data in GIS database.
Due to financial limitation it was impossible to have a mobile system. But using simple technique it was possible to
investigate many factors, which could affect the accuracy and performance of such system. So, this study was done
using professional non-metric 35mm camera. Image coordinates were measured using stereo-comparator and the data
was processed on a personal computer using bundle with self-calibration aerial triangulation program. The description
of the tests which have been carried out as well as the results and their analysis are presented.
1- INTRODUCTION
In 1989, the Center for Mapping of the Ohio State University established a major research program that focuses on the
development of Mobile Mapping Systems (MMS). These devices capture a comprehensive set of land-related data from
airplanes, cars, or trains. Spatial positions and attributes of objects are extracted automatically on the mobile platform or
during post-processing, and are immediately transferred to a multi-media geographic database (Novak, 1995).
The University of Calgary and GEOFIT INC., a high-tech company in Laval, Quebec, Canada have Jointly developed
the same system The system named VISAT, stands for Video-Inertial-SATellite and integrates inertial and GPS
technology with a cluster of CCD cameras (El-Sheimy, 1996 & Li , 1996).
The main objective of this research is to study some of the factors affecting the accuracy of any close range
photogrammetric system such as the mobile mapping. The study area was a road 12mx100m at Assuit University
campus. Professional non-metric (Voigatlander) 35 mm camera, mounted on a tripod, has a bubble for adjusting the
horizontalty and has a handle with graduation for rotating was employed with black and white film as a data acquisition
system. Natural points were selected as control and check points. Their coordinates were estimated using field survey
techniques. Fig.1 illustrates the study area and the positions of camera stations and the object points (both control &
check points.)
Image coordinates were measured four times using a stereocomparator and the average was used for data processing.
The accuracy of the measurements can be assumed 2 or 3 microns. A Bundle adjustment with Self-Calibration (BSC)
program developed and written by Novak from Ohio State University was utilized for photogrammetric triangulation.
Bundle adjustment is an analytical method used to compute accurate object space coordinates of points from their
photographic coordinates. Basically, a bundle is created by each exposure of a camera. The perspective center and the
points in the image define this bundle in a local image coordinate system. The bundle solution tries to shift and rotate
these bundles of light-rays so that they fit to some given control points. Additionally constraints can be included such as
distances measured between object points or perspective centers, to further stabilize the solution (Novak 1991). Bundle
adjustment can also be extended to calibrate the cameras and solve for additional parameters to model distortions of the
images. These parameters, as well as, an open interior orientation, help to fit the bundles to the object control in a better
way.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B5. Amsterdam 2000. 17