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Dean Merchant
PHOTOGRAMMETRIC RESECTION DIFFERENCES BASED
ON LABORATORY vs. OPERATIONAL CALIBRATIONS
Dean C. MERCHANT
Topo Photo Inc.
Columbus, Ohio USA
merchant.2@osu.edu
KEY WORDS: Photogrammetry, Calibration, GPS, Resection
ABSTRACT
Combinations of airborne sensors, including photogrammetric cameras, Global Positioning System and others, give rise
to need for system calibration. This paper discusses results of comparisons of GPS to photogrammetrically resected
camera station coordinates obtained by both laboratory and in situ calibrations. Systematic influences produced by the
aerial environment on the resected elevations were found to produce errors as much as one part in 730 of the flight
height above ground for the open-ported aerial system.
1. INTRODUCTION
Recent interests in combining camera imagery measurements with information from additional sensors for
photogrammetric purposes has led to concern about systematic spatial or orientational errors relating the camera to the
object space and to the added sensors. One of these concerns is the role played by calibration in relating the camera
exposure station coordinates to those provided by the Global Positioning System (GPS).
This paper presents comparisons of camera station coordinates obtained from photography at typical mission altitudes
ranging between 1200 to 5800 meters over a test range to those obtained by GPS. The comparison is done for
resections based both on imagery corrected by laboratory and by in situ [operational] calibration results. Each
photograph tested contained a large series of well-distributed images of targets. All targets were related by GPS ground
surveys to a three-dimensional accuracy of better than 2 cm. The GPS base station during all flights was located within
ten kilometers of exposure stations.
Results indicate a strong influence of the systematic error in those applications using a conventional laboratory based
calibration. Operational camera calibrations based on in-flight imagery demonstrated substantially smaller bias errors
in elevation. A typical bias between laboratory based resected results and GPS elevations for flights in an open-ported
aircraft at 1245 meters above ground elevation was 1.7 meters. For the flight altitude, this represents a systematic error
of one part in 730 of the flight height, a value equal to at least an order of magnitude greater than experienced when
conventional ground control methods are used to control the photogrammetric process. Real data examples from both
pressurized and un-pressurized aircraft are presented.
2. BACKGROUND
It has long been recognized that an environmental influence exists in the metric characteristics of the aerial
photogrammetric system. Duane Brown [1969] demonstrated an order of magnitude improvement in spatial accuracies
by applying the bundle block adjustment with self-calibration to film-based images obtained by the United States Air
Force (USAF) USQ-28 system flying at 6100 meters over the McClure test range in Ohio. This in situ approach to
calibration clearly demonstrated the existence of systematic influences due to environment.
Brown's results, approaching one part in 300,000 of the flight height, motivated a second experiment that was
conducted by the USAF using a Zeiss RMK-AR 15/23 camera [Merchant, 1974]. In this experiment, Mt. Graham in
eastern Arizona provided a significant depth of control field to permit separation of the linear elements of interior from
exterior orientation. From a flight height of about 3050 meters above the base of Mt. Graham, points with an elevation
difference of 915 meters were imaged on a single photo. This imagery, combined with imagery from the more dense
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B3. Amsterdam 2000. 571
